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Effect of increasing temperature on space requirements of group housed finishing pigs
Applied Animal Behaviour Science 138 (2012) 229–239
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Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
Effect of increasing temperature on space requirements of group housed finishing pigs Hans A.M. Spoolder a,∗ , André A.J. Aarnink a , Herman M. Vermeer a , Johan van Riel a , Sandra A. Edwards b a b
Wageningen UR Livestock Research, PO box 65, 8200 AB Lelystad, The Netherlands School of Agriculture, Food and Rural Development, Newcastle University, Agriculture Building, Newcastle Upon Tyne, NE1 7RU, UK
a r t i c l e
i n f o
Article history: Available online 2 March 2012 Keywords: Pig Space requirement Temperature Lying behaviour
a b s t r a c t For groups of pigs to cope adequately with their housing conditions they need sufficient static space (occupied by the body of the pig), activity space (for movement between different functional areas and behaviours relating to these) and interaction space (for appropriate social behaviour). Estimates for static space have been presented for thermoneutral conditions, but are expected to increase substantially as temperature increases. The present paper models the relationship between ambient temperatures above the comfort zone, and thermoregulatory lying behaviour in finishing pigs. Estimates of the effect of posture on floor occupation were obtained and presented as ‘k-values’ (k = floor area occupied (m2 )/body weight2/3 (kg)) to correct for the effect of pig size. A literature review was conducted to collect information on three aspects of lying behaviour: lying frequency, posture (lateral, semi lateral or ventral lying) and level of space sharing (huddling) in response to increasing temperatures. The lowest and highest values found were: increase in lying down: 0.2–0.66%, reduction in space sharing: 1.7–4.9% and increase in lateral vs sternal lying: 0.8–2.3% per ◦ C temperature increase. Extrapolation of k values in the comfort zone to T = 31 ◦ C suggests a range of k-values from k = 0.0331 to k = 0.0385 for static space. In the second part of this paper we analyse video data from a pig building in which groups of 18 pigs were kept in large pens (1.67 m2 per animal) at temperatures ranging from 16 to 32 ◦ C. We find a value of k = 0.0339 at T = 31 ◦ C for static space, which is at the lower end of the range predicted from literature. A possible explanation for this relatively low additional space requirement is that the animals coped by increasingly using the slatted area (with sprinkler system) as a lying area. The study confirms earlier suggestions that the amount of space required by EU legislation is insufficient for pigs at the end of the finishing period, even at relatively low temperatures. In situations where the average room temperature exceeds the comfort zone, pigs need additional space to cope with their housing system, or alternative methods to cool themselves down. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Commercial finishing pigs are almost exclusively kept in groups, typically at group sizes of up to 20 pigs. It has been
∗ Corresponding author. Tel.: +31 320 293532; fax: +31 320 238050. E-mail address: [email protected] (H.A.M. Spoolder). 0168-1591/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2012.02.010
suggested that keeping them in large groups (50–2000 pigs) has several advantages (e.g. Vermeer and Hoofs, 1994; Wolter and Ellis, 2002), and an increasing number of farmers is moving towards large group housing systems (e.g. Penny, 2000; Honeyman, 2005; EFSA, 2007). The beneficial effects of keeping finishers in large groups may be associated with an increase in available total space, even at a constant individual space allowance. However, we are only
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starting to understand how pigs cope with (a lack of) space available to them in group housing systems. The amount of space required by group housed finishing pigs is determined by a number of factors such as the size of the animal, the social dynamics of the group and the design of the pen. Another aspect known to affect space requirement is ambient temperature. Pigs are unable to sweat (Ingram, 1965) and rely to a large extent on behavioural measures to lose excess heat. With increasing temperatures they will reduce their general level of activity, reduce feed intake, minimise physical contact with other pigs, prefer to lie and wallow in wet parts of the pen (e.g. the dunging area) and lie laterally to increase surface contact with the floor (SVC report, 1997; Huynh et al., 2005). Most of the behavioural responses are related to qualitative or quantitative aspects of floor space: group housed pigs cope with increasing temperatures by using more space. Although space requirements of pigs in relation to their body size (and to a lesser extent to group size) have been estimated and empirically verified, a direct relationship between ambient temperature and area occupied by the group has not yet been estimated. In the present paper we aim to determine this relationship in two steps: (a) by modelling the consequences of increased temperatures on behavioural changes and resulting space requirements described in literature, and (b) by using an existing dataset to support or refute the modelling outcomes. 2. Theoretical background 2.1. Determining space requirements Group housed pigs need space to support three main purposes: static space (occupied by the body of the pig), activity space (for, e.g. spatial separation of functions such as feeding and excretion) and social space (for appropriate social behaviour) (Petherick, 1983). It is argued that each of these can be assessed separately, and that their sum equates to the total space requirement for the animal. EFSA (2005) continues Petherick’s (1983) analyses and reviews the three functions in more detail. Activity space and social space are the most difficult two to quantify. In considering activity space, ‘functional areas’ have to be taken into account; that is parts of the pen which are used by the pigs for different purposes (such as sleeping, excretion and feeding). To estimate the required amount for these, EFSA (2005) discusses three main points. Firstly, the amount of space needed per pig should be considered separately for each area. Lying and feeding space can be estimated (see below), but area required for excretion is less easy to quantify (and dependent on, e.g. temperature and group size). Secondly, functional areas can overlap and form a ‘multi-functional area’. For example, in simultaneous feeding systems the lying area will overlap with the feeding area (as these events do not take place at the same time) and similar, but less desirable, overlap of functions may occur when ambient temperatures increase and pigs increasingly lie in the dunging area. Finally it is considered that the size of the group has some effect on the space required for each functional area per pig: the use of the dunging area being the most obvious example of this.
When considering social space, there are two elements to consider: pigs need space to avoid being in constant physical contact (‘personal space’), and pigs also need space to engage in social interactions (e.g. fighting, mounting and expression of appropriate social signals). Neither of these can easily be quantified, although some attempts have been made (e.g. Jensen, 1982; Baxter, 1985; Kay and Spoolder, 1997). For static space requirements it is easier to make a quantitative assessment: the amount of space a body occupies can be measured relatively easily. Factors to take into account for this are the size (weight) of the animal, the posture it assumes and the level of space sharing, e.g. when animals lie on top of each other (huddling) or when they share a common space envelope. Space allowance for pigs is usually expressed as ‘number of square meters per animal’ and the inverse (stocking density) as ‘number of pigs per square meter’. However, these units of measure are meaningless without taking the age or weight of the animals into account. Petherick (1983) proposed a method to integrate the element of pig size by using a constant (k) linking surface area (A, in m2 ) to the weight of the animal (W, in kg) through the equation A = kW2/3 . This ‘k-value’ has since been used in several studies on space allowance (e.g. Kornegay and Notter, 1984; Edwards et al., 1988; Gonyou et al., 2006) because it allows biological relationships to be interpreted irrespective of age and weight of the animals studied. In a first attempt to determine the minimal amount of static space pigs need at different weights, Petherick and Baxter (1981) took images from pigs from above and drew rectangles around the individual animals, the so called ‘pigtographs’. From these graphs they calculated k values for sternally recumbent lying pigs (k = 0.019) and for laterally recumbent lying pigs with legs extended (k = 0.047). The amount of static space for a standing pig equates to that of a sternally recumbent lying pig (Petherick and Baxter, 1981) and the same can be argued for sitting pigs. However, the amount of static space a group of pigs needs is dependent on the frequency of lying behaviour, the postures adopted and the amount of space shared between animals. Ekkel et al. (2003) looked at these aspects in a study on total area use by groups of lying pigs. Their estimate of an average k = 0.033 per pig confirms earlier suggestions by Petherick (1983) that the value is the same as for a ‘half recumbent’ lying animal. 2.2. Effects of temperature on pig behaviour As previously indicated, an important external factor affecting the k value is the ambient temperature. Petherick (1983) already noted that temperature affects the amount of floor space pigs use, and Ekkel et al. (2003) stress the fact that their k value only applies to thermoneutral conditions. The effect of temperature on required physical space has not yet been quantified. However, it may be possible to estimate the space requirement indirectly, by investigating the behaviours that groups of pigs express when coping with increasing temperatures. Some of these will have a direct effect on the amount of space used. These are: a) the level of inactivity (as expressed by % of pigs lying),
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Table 1 Literature values for percentage change in behaviours for each degree Centigrade increase in ambient temperature.
Huynh et al. (2005) Aarnink et al. (2006) Pedersen et al. (2003) Ducreux et al. (2002)
Weight range (kg)
Temp range (◦ C)
Lying down
Huddling
Lateral lying
58–65 25–105 60–110 70
16–32 18–28 10–28 18–27
0.2% 0.5% 0.66%
−4.9% −3.7% −1.7%
0.8% 1.9% 1.4% 2.3%
b) the degree of contact or space sharing between animals and c) the change in lying posture, e.g. from lying on the sternum to lying semi-laterally or laterally. There is a limited amount of data in the literature to quantify these three effects. Table 1 presents an overview of some of these data. Activity levels are generally reduced as temperatures increase. This means that more pigs will be lying down. Huynh et al. (2005) estimated that for every degree Centigrade increase in temperature between 16 and 32 ◦ C, the number of pigs lying down increased by 0.2%. One year later, Aarnink et al. (2006) published their finding that this should be around 0.5%. A third estimation can be found in a paper by Pedersen et al. (2003). They found in their study that activity levels in the summer reduced from roughly 20 to 8% when temperature increases from 10 to 28 ◦ C. This could be interpreted as an increase in lying behaviour of 12% over 18 ◦ C temperature difference: so approximately 0.66% per ◦ C. Pigs will reduce physical contact with increasing temperatures. Aarnink et al. (2006) found 3.7% less pigs lying against other pigs for every degree Centigrade increase between 18 and 28 ◦ C. Huynh et al. (2005) estimated that for every degree Centigrade increase in temperature the number of pigs huddling (so in contact with each other) decreased by 4.9%. Finally, Pedersen et al. (2003) estimated a reduction in huddling between 10 and 28 ◦ C from roughly 40 to 8% (in pigs of 60–110 kg), so a reduction of 32% over 18 degrees temperature difference. This equates to 1.7% per ◦ C temperature change. However, it is likely that the decrease was not linear and a faster decrease per degree can be expected in the higher temperature range. The posture of lying pigs changes in response to increased temperatures. Lying laterally increases the contact area of body surface with the floor and promotes the loss of heat, but also increases the amount of floor in use, compared to lying in a sternal (ventral) posture. Ducreux et al. (2002) found a significant increase in lying laterally when comparing pigs kept at 18 ◦ C with 27 ◦ C. At 18 ◦ C they found 66% lying ventrally vs 34% lying laterally. At 27 ◦ C these figures were 44% vs 55% respectively). This means that over 9 ◦ C lateral lying went from 34 to 55% (i.e. 2.3% per ◦ C). In addition, Aarnink et al. (2006) found 1.9% more pigs lying on their sides for every degree Centigrade, and Huynh et al. (2005) estimated this figure to be 0.8%. Based on their observations in insulated buildings, Pedersen et al. (2003) estimated that lying laterally in the summer increased from roughly 40 to 65%, when temperature increased from 10 to 28 ◦ C. This equates to 1.4% per ◦ C. Savary et al. (2009) found that lateral lying increased when temperature increased from 10 to 20 ◦ C for low weight pigs (<50 kg) and from 10 to 15 ◦ C for middle weight pigs (50–80 kg), and then went down again. Heavy
pigs (>80 kg) reduced their lateral lying with increased temperature, from 10 ◦ C up to about 19 ◦ C after which lateral lying increased slightly. It is relevant to note that in this study pigs shifted their preferred lying location from a solid concrete floor to a slatted floor with increasing temperature. In heavy pigs this shift appeared to be the fastest. Another (fourth) way of coping behaviourally with increased temperatures (and which affects the use of space) is the preference to lie in a cool place, as temperature increases. Pigs will move from an insulated (solid, strawed) floor to a wet and colder place. It is likely that this will also affect the amount of space required, as lateral lying is less needed to loose the same amount of heat on slats, compared to a solid floor. Ducreux et al. (2002) found that 70 kg pigs kept at 27 ◦ C preferred to rest on a concrete or slatted floor instead of a solid floor with litter, compared to pigs kept at 18 ◦ C (44% vs 15% respectively). Pedersen et al. (2003) found an increase in lying in the dunging area when temperature rose above 15–20 ◦ C (in pigs of 60–110 kg). Savary et al. (2009) also found that the slatted floor was more frequently used as temperature increased. Based on their data, they estimated a shift from solid to slatted floor occupation from 0 to 20% for <50 kg pigs between 15 and 20 ◦ C, from 0 to 55% for 50–80 kg pigs between 10 and 28 ◦ C, and from 5 to 60% for >80 kg pigs between 12 and 23 ◦ C. Aarnink et al. (2006) found an increase in number of pigs lying on the slatted floor of approximately 10% per ◦ C for 25 and 45 kg pigs and of approximately 5% per ◦ C for 65, 85 and 105 kg pigs. The temperature at which a maximum number of pigs on the slatted floor was reached decreased from 27.5 ◦ C for 25 kg pigs to 23.2 ◦ C for 105 kg pigs. Finally, Huynh et al. (2005) found, for pigs of 62 kg, an increase of lying on the slatted floor of 2.2% per ◦ C at 50% RH and of 2.9% at 65 and 80% RH. The effect of these changes in floor preference on the amount of space required, are difficult to quantify. They are strongly related to the insulating properties of the two floors and other aspects related to the Upper Critical Temperature (UCT) of the pig. The above data allows rough estimates to be made of the effects that an increase of 1 degree Centigrade has on behaviours related to space requirements: between 0.2 and 0.66% extra pigs will lie down, between 1.7 and 4.9% less space sharing will occur and there will be an increase of between 0.8 and 2.3% of lying laterally rather than sternal lying. 2.3. Estimation of k-value at increasing temperatures The effects of the above factors on required space can be modelled. The Ekkel et al. (2003) figure of k = 0.033, determined under thermoneutral conditions, was used as a
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starting point. In this paper, at 21 ◦ C the proportion of lying pigs during the day was approximately 0.8,1 of which a proportion of 0.672 was lying laterally. The area required for sternal and lateral lying is k = 0.019 and 0.047, respectively (Petherick, 1983). There was a proportion of space sharing of 0.132 for all laterally lying pigs (Ekkel et al., 2003) which means that 13.2% of the space occupied by lateral lying was shared, i.e. the space between the extended legs of one pig was occupied by another pig. Estimation of the k value at T = 31 ◦ C equates to a change in temperature of +10 ◦ C, if 21 ◦ C is used as the starting point in the comfort zone of growing pigs of all weights. The effects of this change on space requirement were calculated using the lowest and highest values found in the literature reviewed previously, namely an increase in lying down of 0.2–0.66%, a reduction in space sharing of 1.7–4.9% and an increase in lateral vs sternal lying of 0.8–2.3%. It can be calculated that the effects of a 10 ◦ C increase in temperature, using the highest values reported in the papers above, result in the following predicted proportions of pigs in different postures: Proportion lying pigs: 0.8 + 10 × 0.0066 = 0.866. Proportion lateral lying (of all lying pigs): 0.672 + 10 × 0.023 = 0.902. Proportion of space sharing (of lateral lying pigs): 0.132 − 0.132 × (10 × 0.049) = 0.067. Proportion of lateral lying space which is not shared: 1 − 0.067 = 0.933. From these highest values, a group average k value for lying pigs can be calculated: k for the proportion of lateral lying pigs: 0.902 × 0.047 = 0.0423. Multiply this space for lateral lying pigs by the proportion of unshared space: 0.0423 × 0.933 = 0.0396. k for the proportion of sternal lying pigs: (1 − 0.902) × 0.019 = 0.0019. Average k for all lying pigs (sternal plus lateral): k = 0.0019 + 0.0396 = 0.0414. The average static space required for the whole group can be calculated by multiplying the space for lying pigs by the proportion of lying pigs, and adding the proportion of standing and sitting pigs multiplied by k = 0.019. It follows that k = 0.866 × 0.0414 + 0.134 × 0.019 = 0.0385. This equates to an average space required to support the static body of 0.884 m2 for groups of 110 kg pigs at 31 ◦ C. Conversely, when the lowest values found in the literature are used (increase in lying down: 0.2%; increase in lateral vs sternal lying: 0.8%; reduction in space sharing: 1.7%), it can be calculated that the average k value for lying pigs is 0.0362, and the average k for the whole group
1 At night more pigs were lying, and less activity space was used. For comparison with the empirical data presented later in this paper, we prefer to use Ekkel’s estimate for proportion of pigs lying during the day referred to in his Discussion section.
(lying, sitting and standing pigs) is 0.0331. This equates to 0.760 m2 for a 110 kg pig at 31 ◦ C. The above model calculations are by definition an approximation of what happens to static space requirements when temperature increases. In the second part of this paper an existing dataset was analysed to test the hypothesis that, in a conventional pig building with ample space, the k value will increase with increasing temperature, and the static space requirement at T = 31 ◦ C is between k = 0.0331 and k = 0.0385. 3. Collection and analyses of empirical data The data for this study were obtained from a series of photographs taken from pens in the Comfort Class pig building in Raalte, The Netherlands (De Greef et al., 2011). In this building the behaviour and performance of finishing pigs housed in different group sizes and at different stocking densities was observed from 2006 to 2009. The studies in the Comfort Class system were not designed to investigate the effect of temperature on space use per se, and there are several limitations to the dataset (see below). However, they can provide an interesting cross comparison with data from the literature synthesis presented data above. The stocking density study in the Comfort Class building did not require formal ethical approval from the Animal Experimentation Committee. 3.1. Animals and housing The Comfort Class facility is a naturally ventilated house (30 m × 20 m), with curtains in the side walls above 1.50 m height, regulated by outdoor sensors monitoring wind speed, wind direction and temperature. The building contains three ‘blocks’ of four 30 m2 pens each (Fig. 1). A standard pen measured 3.76 m × 8 m and contained 18 pigs, resulting in an average space allowance of 1.67 m2 per animal. Each pen had three separate functional areas: a kennelled strawed area (3.76 m × 2 m), an open concrete solid-floored lying area (3.76 m × 4 m; not insulated) and a concrete slatted dunging area (3.76 × 2 m). The pigs were kept in these pens from 20 to 100 kg live weight, and were of mixed sex (50% barrows, 50% gilts). They were fed ad libitum from several feed hoppers. At room temperatures above 25 ◦ C water was sprinkled above the slatted floor for 40 s every 30 min. Temperature was monitored and recorded continuously at room level. Above each pen, a colour infrared camera (TeleConnect, model TC516CEXH) was mounted from the roof. The view of each camera covered the full pen except the covered lying area. Each camera took a picture at 15 min intervals throughout the 24 h day. 3.2. Observations on space use The photographs were used to estimate the amount of space used by lying pigs, and to determine the location (kennel, solid floor or slatted floor) of the animals. For the assessment of space occupied, the photographs were projected onto an Excel sheet consisting of square cells (Fig. 2a and b). The dimensions of these square cells
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Fig. 1. Floor plan and cross section of a block of four pens in the Comfort Class building.
could be related to the dimensions of the pen areas on the photograph, and it was estimated that an average square in the solid floor area represented 0.028 m2 . Because of visual distortion a separate value was calculated for the slatted area. For this it was estimated that a square cell represented 0.047 m2 . It is important to note that these two figures represent an average for each of these two areas, which means that the size of a square was overestimated in the middle of the picture and underestimated at the sides. For each photograph, rectangles were fitted around lying pigs (Fig. 2a), similar to the rectangles used by Petherick and Baxter (1981). Standing and sitting pigs were ignored. The photograph was then removed and all square cells in the Excel sheet covered by a rectangle were given the same number. For individual pigs the floor area occupied was calculated as the number of squares in the rectangle multiplied by the area each square represented. Overlapping rectangles were collectively marked as a ‘cluster’, and all square cells in such a cluster were given the same number (Fig. 2b). The area occupied by a cluster was calculated as the number of squares with the same number multiplied by the area a square represented, and divided by the number of pigs in that cluster. Individual pigs or clusters lying in the dunging area were treated separately from pigs lying on the solid floor. Pigs which were entirely or partly in the kennel were assumed to be lying, but not included in the estimations for average space occupation per pig.
Random effects of batch, pen (within batch), date (within pen) and cluster (within date) were included in the mixed model. The space requirement data were considered normally distributed (checked by analyses of residuals). The data structure here was slightly unbalanced because individual pens could have a different number of clusters at the same time (date). For analyzing the proportion of lying animals or the preference of the location, the data structure was reorganised where date (within) pen was the experimental unit. The data of the percentage of lying animals were analysed with a logistic model (Generalized Linear Mixed Model, GenStat, 2002). The preference data were considered as ordinal response data (McCullagh and Nelder, 1989), since the kennel provides the most thermal protection and slatted floor provides the least. The following ordinal response model was used:
3.3. Statistical analyses
Within each series of photographs from one of the ten pens selected, only pictures from days on which the ambient temperature reached 16 ◦ C or more were used. To minimise dependencies between lying patterns, only one
The data analysis was conducted using the statistical programming language Genstat version 8 for Windows.
log it(j (x)) = ˛j − ˇT x, j = 1, . . . , K − 1
(1.2)
With k − 1 intercept terms or cut-off points (˛j ), were k (number of classes) is 3, ˇT x is a short notation of the model terms in model 1.1, and is the cumulative probability for category j. 4. Results of empirical study 4.1. Useable photographs
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Fig. 2. (a and b) Illustration of the way the area used by the lying animals was recorded.
picture per day per pen was analysed. The warmest part of the day was chosen from which to select a picture. A total of 276 photographs were thus selected for further analyses, from 4 batches. The groups in batches 1–3 were followed from December 2006 to December 2007, and in batch 4 during the summer of 2009 (Table 2). The temperature during the observation periods ranged from 16 to 32 ◦ C. Almost all pictures used (268 out of 276) were taken between 12:00 and 18:00 h, with an ‘average time’ of 15:15 h. The number of photographs taken during higher ambient temperatures was relatively low, but the observations were relatively evenly distributed over the total growing-finishing period (Table 3).
Table 2 Description of batches of pigs used in the study. Dates Batch 1 Batch 2 Batch 3 Batch 4
15 December 06–3 April 07 12 April 07–16 July 07 7 August 07–10 December 07 12 May 09–18 August 09
Temp range (◦ C) 16.1–19.4 16.3–31.9 16.2–26.0 16.0–27.8
Av temp 17.6 25.2 18.9 21.6
4.2. Standing behaviour and distribution of pigs in the pen The posture of the visible pigs was affected by temperature: pigs were standing less with increasing temperature
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Table 3 Number of photographs analysed per temperature category and weight category. Temperaturea 16
18
20
22
24
26
28
30
20–40 kg 40–60 kg 60–80 kg 80–100 kg 100+ kg
8 20 21 20 0
0 4 15 18 3
4 24 10 10 5
4 4 7 10 4
5 10 9 9 1
0 2 7 1 3
2 1 8 7 6
6 0 7 0 1
29 65 84 75 23
Total
69
40
53
29
34
13
24
14
276
Temperature truncated to 2 ◦ C categories: 16 ◦ C means all temperatures between 16 and 18 ◦ C.
70 60
% of pigs
(P = 0.007, F = 7.28, df = 298) (Fig. 3). The line of best fit was linear and equated the percentage of non-lying pigs to 24.337 − 0.5815 × T (in ◦ C). This suggests that for every degree increase in temperature, the number of non-lying pigs decreases by 0.58%, (or an increase of lying pigs (visible and in the kennel) of 0.58%). The number of pigs lying in different areas of the pen changed with increasing temperature as well as with increasing pig weight (P < 0.001). There was no interaction between these two factors (F = 2.36, df = 212, P = 0.126). The location preference of the animals was modelled using an ordinal response model (corrected for batch and pen). As body weight increased, pigs were observed less in the kennel and more on the slatted area. An increase in ambient temperature had a similar effect (Fig. 4). At low temperatures the kennel and the solid floor were predominantly used when lying, and hardly any pigs lay on the slatted floor. At high temperatures the slats were increasingly preferred, at the expense of the solid floor and the kennelled area. The average increase per degree Centigrade was 1.39% (calculated as the average percentage on the slatted floor at 30 ◦ C, minus the average at 16 ◦ C, and divided by 14 degrees).
50 40 30 20 10 0 16
18
20
22
24
26
28
30
16
18
20
22
24
26
28
30
16
18
20
22
24
26
28
30
70 60
% of pigs
a
Total
50 40 30 20 10 0
70
Over the full temperature range of 16–32 ◦ C, the model which described the relationship between the floor area occupied by lying pigs and the two factors Weight and
% of pigs
60
4.3. Floor area occupation by lying pigs
50 40 30 20 10
% standing + sitting pigs
0 25
Temp 20 Fig. 4. Preferred location for pigs at different temperatures (modelled), top: 25 kg, middle: 65 kg, bottom: 105 kg body weight. Thin solid lines represent lying in the kennelled area, thick solid lines are the solid lying area, dashed lines the slatted dunging area.
15 10 5
Temp was:
0 15
20
25
30
35
Temp Fig. 3. The percentages of standing or sitting pigs in relation to ambient temperature (out of a total of 18 pigs per pen, with all pigs in the kennel assumed to be lying).
Ln (Area) = −0.6064 + 0.0044 × Temp + 0.6832 Weight (2.1) In this model, both ambient temperature and body weight were standardised so that model estimates were
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calculated within the range of observations. The intercepts were set at T = 20 ◦ C, and weight = 65 kg (and not at 0 ◦ C and 0 kg respectively), therefore: Temp = ambient temperature minus 20 ◦ C. Weight = Ln (body weight/65 kg). The amount of floor space a pig uses to lie on increased with increasing body weight (P < 0.001), as well as with increasing ambient temperature (P < 0.05). There was no interactive effect (P = 0.12) between these two factors on floor surface used. 4.4. k-Value estimation The observations on lying space occupation in relation to temperature and weight can be used to estimate k values, which link lying area to temperature, irrespective of the pig’s weight. Therefore the relationship (model 2.1 above) between the floor area occupied and the two factors Weight and Temp can be rewritten into a calculation for the k value. Area = (e−0.6064 ) × (1/65)
0.6832
× e0.0044×Temp
× (body weight)0.6832
(2.2)
Or : Area = k-value (varying by temp) × (body weight)0.6832
(2.3)
It is interesting to note that the conversion from the three (weight) to two (area) dimensions of a pig body in our estimated model (2.3) equals 0.6832. This is very close, but different, to the theoretically correct value of 2/3 (i.e. 0.6667). It is likely that small errors, e.g. due to parallax effects in the observations are to blame for this. If we correct for this, back to the value of 2/3, we find k-value = (e−0.6054 ) × (1/65)
2/3
× e0.0044×Temp
(2.4)
The modelled best fit through the k-values for all lying pigs associated with temperatures increasing from 16 to 31 degrees (averaged at 1 ◦ C increments), suggests a k-value of k = 0.0350 at T = 31 ◦ C (Fig. 5).
0.039
K-value
0.037 0.035 0.033 0.031 0.029 0.027 0.025 15
20
25
30
Temp (averaged per 1 oC) Fig. 5. k-Value for lying pigs in relation to ambient temperature between 16 and 31 ◦ C (averaged per 1 ◦ C). Superimposed on these data is the modelled k value (increasing with temperature).
Estimation of the group mean k value for static space (body space when lying, sitting or standing) requires information on the proportion of lying pigs. This can be estimated from the equation in paragraph 4.2 above: 24.337 − 0.5815 × T (in ◦ C). At 31 ◦ C this is 6.31%. That means that a proportion of 0.063 of the pigs is standing, and therefore 0.937 is lying. Using the values from our empirical dataset, the group mean k-value for static space requirement at 31 ◦ C is: 0.937 × 0.0350 + 0.063 × 0.019 = 0.0339, equivalent to 0.78 m2 for a 110 kg pig. 5. Discussion Groups of finishing pigs cope with increasing temperatures by changing their behaviour. Some of these changes require additional ‘static’ space (the space physically occupied by the body of a pig). There are limited data available in the literature to quantify the effects of temperature on static space requirements. In this paper we present some data from peer reviewed publications and estimate that the k value at 31 ◦ C will be between k = 0.0362 and 0.0414 for all lying pigs, and between k = 0.0331 and 0.0385 for mean static space requirement of all pigs in the group. The present paper then proceeds to study actual changes in space required, in an ongoing study of group-housed finishing pigs. These empirical data suggest a k value for all lying pigs of k = 0.0350, and for total static space of k = 0.0339. This means that for static (body) space alone, at 31 ◦ C, a 110 kg pig will need on average 0.78 m2 . The estimated k value based on the pig study (0.0339) is at the lower end of the data modelled on the basis of studies in the literature (range 0.0331–0.0385). It appears that the pigs in the Comfort Class system are able to cope with increasing temperatures by using up less additional space, compared with the theoretically derived space requirements of pigs in other studies. There are several possible explanations for this, related to the design of the building. First of all, the Comfort Class system has three different functional areas: the kennel, a solid (lightly strawed) open lying area and a slatted dunging area. The pigs in this study responded to increasing temperatures not just by increasing the space they occupied, but also by moving to cooler parts of the pen: from the kennel to the solid floor, and from the solid floor to the slats. This behaviour is consistent with that observed in other studies (e.g. Ducreux et al., 2002; Aarnink et al., 2006; Savary et al., 2009; Hillmann et al., 2004). Initially this may have resulted in a slight increase in lying space required: Hillmann et al. (2004) suggested that, with increasing temperatures, pigs will stop huddling first (i.e. increase lying without contact), before increasing their lying behaviour in the dunging area. They did not study the lying posture, but it seems likely that the shift to lying in the dunging area does not immediately result in an increased space requirement, as pigs will initially lie in a sternal position. A meta-analysis of existing data by Averos et al. (2010) also suggests that pigs on a slatted floor use less lying space compared to pigs on a solid floor, in otherwise comparable circumstances. It is relevant to note that from a hygiene point of view the increased lying behaviour in the dunging area has negative consequences for the performance
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of the system as a whole: pigs will increasingly use the solid floor as dunging area, resulting in dirtier pigs and pens. A second factor which will have affected the amount of space the pigs used is the showering system which was activated at temperatures above 25 ◦ C. Pigs which moved to the slatted floor generally had only one behavioural way to cope with a further increase in temperature, which was to increase the contact between body and floor by lying laterally. The showering system will have slowed down the change to lateral lying, although this is still likely to have increased as temperature went up. Virtually all pictures used were taken between 12:00 and 18:00 h, since this is when the highest ambient temperatures occur in practice, and therefore reflect the afternoon behaviour of ad libitum fed finishing pigs. It can be argued that the samples therefore do not represent the ‘average’ space required by the animals during the 24 h day. The ‘group k-value for static space’ depends on the proportion of pigs lying, and will be higher if all pigs lie down (providing a fixed proportion of all lying pigs lies laterally, as sternal lying requires an equal amount of space as standing). Although the present paper did not investigate the effect of time, it is known from other studies (e.g. Ekkel et al., 2003) that the afternoon time frame provides a good representation of the lying behaviour during the day in ad lib. fed finishers. However, at night, pigs will decrease activity levels and lie down more. This means that the empirical data in the present study are an underestimation of the average lying space required during the 24 h day, particularly if high temperatures persist into the night. If activity space or total space is considered, the prediction of space required gets more complex. EFSA argues that being active (other than simply standing) requires at least twice the k value for a standing pig (so 2 × 0.019 = 0.038). This of course is only an estimate, but is higher than the average lying space required (k = 0.033), although still lower than the space required for lateral recumbent lying (k = 0.047) which is the predominant posture at night (Ekkel et al., 2003). Therefore, it can be hypothesised that the afternoon data used in the empirical part of this study provides an underestimate of lying space requirement, as well as an underestimate of static + activity space required, over the 24 h day. The amount of space currently offered in pig buildings depends on legislative and economic factors. In the EU the minimum space allowance is prescribed in EU Directive 91/630/EC, and approximately equates to k = 0.030 (Spoolder et al., 2000). This k-value matches results from earlier work in which an economic optimum was calculated, based on pig growth and feed efficiency at different space allowances, and the associated investment and maintenance costs for the accommodation (Edwards et al., 1988). The EC legislation makes it compulsory for pigs in the weight category of 85–110 kg to be kept at a minimum of 0.65 m2 per individual. Intensively housed finishing pigs are generally kept in the same pen for the whole of the finishing period (from roughly 30 to 110 kg live weight), and thus at 0.65 m2 . To estimate if this is sufficient to accommodate the body dimensions of the pig (static space) as well as activities such as feeding and
237
eliminating in a separate dunging area (activity space), further development of the model is needed. From the theoretical background it is clear that the amount of static space only relates to the physical dimensions of the body of the animals in the group, as affected by posture and level of space sharing. In addition to this, activity space and social space should be taken into account when calculating the total amount of space required (Petherick, 1983). These two components are very hard to estimate. For social space the amount required is very much dependent on the circumstances, as social activities are unevenly distributed in time and space. Play behaviour decreases as pigs get older and aggressive behaviour is either related to the group’s social stability or to competition for access to resources. However, EFSA (2005) did attempt to quantify activity space under thermoneutral conditions. Starting from k = 0.033 (Ekkel et al., 2003), they argued that for active pigs (approximately 20%) the k value can be estimated to be 2 × 0.019 = 0.038. This means that they added an area equivalent to a standing pig for every sitting or standing animal. This space would then be available for the active animal to walk, explore, root, etc. EFSA also considered dunging and feeding behaviour. They assumed that for a group of ten pigs one extra pig space (k = 0.019) is required to separate the dunging area from lying and activity area (so k = 0.0019 per animal). However, EFSA (2005) did not add additional feeding space to their estimates for k, as space required for feeding can be substituted for activity space (when pigs feed consecutively) or static (lying) space (when pigs feed simultaneously). These estimates relating to activity space can be interpreted in relation to increased temperature by taking into account the proportion of active pigs. In the group housing system studied in this paper, this proportion of active pigs was estimated to be 0.063 at 31 ◦ C. EFSA (2005) suggests these pigs should have twice the amount of static space (k = 0.038), and for every pig a tenth of the space for a standing pig should be added to provide a separate dunging area (k = 0.0019). Therefore, for the groups studied in the Comfort Class pig building, the k-value for static + active space at 31 ◦ C is: 0.937 × 0.0350 + 0.063 × 0.038 + 0.0019 = 0.0371, equivalent to 0.85 m2 for a 110 kg pig. The predicted effects of temperature at different bodyweights on the amount of physical (static) space pigs plus activity space that pigs need, can be compared to the current EU legislation (Fig. 6). The predictions are based on the empirical data in this paper, and the model derived from them. The data suggests that if the legal minimum is applied, pigs heavier than 85 kg are all housed at stocking densities which are too high. Fig. 6 also suggests that the effects of temperature are relatively modest. However, the effects of temperature in this dataset were mitigated by the circumstances under which the animals were kept. They were housed in a naturally ventilated building, had access to different functional areas and at temperatures over 25 ◦ C a showering system was triggered. For conventional group housing systems, it is likely that the increase in space required to cope with increasing temperatures is closer to the upper end of the
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0.9
Area (m2)
0.8 0.7
105 kg
0.6
85 kg
0.5
65 kg
0.4
45 kg
0.3
25 kg
0.2
A=0.65m2
0.1 0 16
19
22
25
28
31
o
Temp ( C) Fig. 6. Modelled estimates of the amount of static space plus activity space required for pigs at different weights, and at increasing temperatures, in relation to common European practice of A = 0.65 m2 .
range identified from literature, than the modelled data from the Comfort Class. 6. Conclusion It can be concluded from this study that the amount of space pigs require to cope behaviourally is affected significantly by increasing temperatures. In addition, the study confirms earlier suggestions that the amount of space required by EU legislation is insufficient for pigs at the end of the finishing period, even at relatively low temperatures. In situations where the average room temperature exceeds those in the comfort zone, pigs need additional space to cope with their housing system, or alternative methods to cool themselves down. Conflict of interest None. Acknowledgments The authors want to thank Agnes de Wit for her help in analysing the data. We gratefully acknowledge the financial support for this project by the Dutch Ministry of Agriculture, Nature Management and Food Quality. For her part in this study, SAE would like to thank the European Community for their financial contribution via the Sixth Framework Programme’s Integrated Project QPORKCHAINS (FOOD-CT-2007-036245). References Aarnink, A.J.A., Schrama, J.W., Heetkamp, M.J.W., Stefanowska, J., Huynh, T.T.T., 2006. Temperature and body weight affect fouling of pig pens. Journal of Animal Science 84, 2224–2231. Averos, X., Brossard, L., Dourmad, J.Y., De Greef, K.H., Edge, H.L., Edwards, S.A., Meunier-Salaun, M.C., 2010. Quantitative assessment of the effects of space allowance, group size and floor characteristics on the lying behaviour of growing-finishing pigs. Animal 4 (5), 777–783. Baxter, M., 1985. Social space requirements of pigs. In: Zayan, R. (Ed.), Social Space for Domestic Animals. Martinus Nijhoff Publishers, Dordrecht, The Netherlands, pp. 116–127. De Greef, K.H., Vermeer, H.M., Houwers, H.W.J., Bos, A.P., 2011. Proof of Principle of the Comfort Class concept in pigs – experimenting in the midst of a stakeholder process on pig welfare. Livestock Science 139, 172–185.
Ducreux, E., Aloui, B., Robin, P., Dourmad, J.-Y., Courboulay, V., MeunierSalaün, M.-C., 2002. Ambient temperature influences the choice made by pigs for certain types of floor. Journées de la Recherche Porcine 34, 211–216. Ekkel, E.D., Spoolder, H.A.M., Hulsegge, I., Hopster, H., 2003. Lying characteristics as determinants for space requirements in pigs. Applied Animal Behaviour Science 80, 19–30. EC, 1991. Council Directive 91/630/EC of 19 November 1991 laying down minimum standards for the protection of pigs (OJ L 340,11.12.1991, p. 33). Edwards, S.A., Armsby, A.W., Spechter, H.H., 1988. Effects of floor area allowance on performance of growing pigs kept on fully-slatted floors. Animal Production 46, 453–459. EFSA, 2005. The welfare of weaners and rearing pigs: effects of different space allowances and floor types. The EFSA Journal (2005) 268, 1–19. EFSA, 2007. Animal health and welfare in fattening pigs in relation to housing and husbandry. The EFSA Journal (2007) 564, 1–14. GenStat, 2002. Reference Manual, Release 6.1. VSN International, Oxford, UK. Gonyou, H.W., Brumm, M.C., Bush, E., Davies, P., Deen, J., Edwards, S.A., Fangman, T., McGlone, J.J., Meunier-Salaun, M.-C., Morrison, R.B., Spoolder, H., Sundberg, P.L., Johnson, A.K., 2006. Application of broken line analysis to assess floor requirements of nursery and growerfinisher pigs expressed on an allometric basis. Journal of Animal Science 84, 229–235. Hillmann, E., Mayer, C., Schrader, 2004. Lying behaviour and adrenocortical reactions as indicators for the thermal tolerance of pigs of different weight. Animal Welfare 13, 329–335. Honeyman, M.S., 2005. Extensive bedded indoor and outdoor pig production systems in USA: current trends and effects on animal care and product quality. Livestock Production Science 94 (June (1–2)), 15–24. Huynh, T.T.T., Aarnink, A.J.A., Gerrits, W.J.J., Heetkamp, M.J.H., Canh, T.T., Spoolder, H.A.M., Kemp, B., Verstegen, M.W.A., 2005. Thermal behaviour of growing pigs in response to high temperature and humidity. Applied Animal Behaviour Science 91, 1–16. Ingram, D.L., 1965. The effect of humidity on temperature regulation and cutaneous water loss in young pigs. Research in Veterinary Science 6, 9–17. Jensen, P., 1982. An analysis of agonistic interaction patterns in grouphoused dry sows – aggression regulation through an ‘avoidance order’. Applied Animal Ethology 9, 47–61. Kay, R.M., Spoolder, H.A.M., 1997. Improving the welfare of newly weaned sows by minimising aggression during mixing. Study 1: the effect of flight distance on aggression and skin damage. MAFF report, ADAS Terrington. Kornegay, E.T., Notter, D.R., 1984. Effects of floor space and number of pigs per pen on performance. Pig News and Information 5 (1), 23–33. McCullagh, P., Nelder, J.A., 1989. Generalized Linear Models, 2nd ed. Chapman & Hall/CRC, Boca Raton, Florida. Pedersen, S., Sousa, P., Andersen, L., Jensen, K.H., 2003. Thermoregulatory behaviour of growing-finishing pigs with access to outdoor areas. In: Agricultural Engineering International, CIGR, Manuscript BC 03 002, p. 16. Penny, P.C., 2000. Effect of modification to pen design formations on the performance of weaned pigs housed in large group systems. Journal of Animal Science 78 (Suppl. 1), 238.
H.A.M. Spoolder et al. / Applied Animal Behaviour Science 138 (2012) 229–239 Petherick, J.C., 1983. A biological basis for the design of space in livestock housing. In: Baxter, S.H., Baxter, M.R., MacCormack, J.A.C. (Eds.), Farm Animal Housing and Welfare. Martinus Nijhoff Publishers, Dordrecht, pp. 103–120. Petherick, J.C., Baxter, S.H., 1981. Modelling the static spatial requirements of livestock. In: MacCormak, J.A.D. (Ed.), Modelling, Design and Evaluation of Agricultural Buildings. CIGR Section II Seminar, Scottish Farm Buildings Investigation Unit. Bucksburn, Aberdeen, pp. 75–82. Savary, P., Gygax, L., Wechsler, B., Hauser, R., 2009. Effect of a synthetic plate in the lying area on lying behaviour, degree of fouling and skin lesions at the leg joints of finishing pigs. Applied Animal Behaviour Science 118, 20–27.
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Spoolder, H.A.M., Edwards, S.A., Corning, S., 2000. Legislative methods for specifying stocking density and consequences for the welfare of finishing pigs. Livestock Production Science 64, 167–173. SVC, 1997. The Welfare of Intensively Kept Pigs – Report of the Scientific Veterinary Committee, adopted 30 September 1997, website: http://europa.eu.int/comm/food/fs/sc/oldcomm4/out17 en.html. Vermeer, H.M., Hoofs, A.I.J., 1994. The effect of weaner group size on performance and profitability. Praktijkonderzoek Varkenshouderij, proefverslag nummer P1.118, pp. 5–6. Wolter, B.F., Ellis, M., 2002. Impact of large group sizes on growth performance in pigs in the USA. Pig News and Information 23, 17N–20N.
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Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
Effect of increasing temperature on space requirements of group housed finishing pigs Hans A.M. Spoolder a,∗ , André A.J. Aarnink a , Herman M. Vermeer a , Johan van Riel a , Sandra A. Edwards b a b
Wageningen UR Livestock Research, PO box 65, 8200 AB Lelystad, The Netherlands School of Agriculture, Food and Rural Development, Newcastle University, Agriculture Building, Newcastle Upon Tyne, NE1 7RU, UK
a r t i c l e
i n f o
Article history: Available online 2 March 2012 Keywords: Pig Space requirement Temperature Lying behaviour
a b s t r a c t For groups of pigs to cope adequately with their housing conditions they need sufficient static space (occupied by the body of the pig), activity space (for movement between different functional areas and behaviours relating to these) and interaction space (for appropriate social behaviour). Estimates for static space have been presented for thermoneutral conditions, but are expected to increase substantially as temperature increases. The present paper models the relationship between ambient temperatures above the comfort zone, and thermoregulatory lying behaviour in finishing pigs. Estimates of the effect of posture on floor occupation were obtained and presented as ‘k-values’ (k = floor area occupied (m2 )/body weight2/3 (kg)) to correct for the effect of pig size. A literature review was conducted to collect information on three aspects of lying behaviour: lying frequency, posture (lateral, semi lateral or ventral lying) and level of space sharing (huddling) in response to increasing temperatures. The lowest and highest values found were: increase in lying down: 0.2–0.66%, reduction in space sharing: 1.7–4.9% and increase in lateral vs sternal lying: 0.8–2.3% per ◦ C temperature increase. Extrapolation of k values in the comfort zone to T = 31 ◦ C suggests a range of k-values from k = 0.0331 to k = 0.0385 for static space. In the second part of this paper we analyse video data from a pig building in which groups of 18 pigs were kept in large pens (1.67 m2 per animal) at temperatures ranging from 16 to 32 ◦ C. We find a value of k = 0.0339 at T = 31 ◦ C for static space, which is at the lower end of the range predicted from literature. A possible explanation for this relatively low additional space requirement is that the animals coped by increasingly using the slatted area (with sprinkler system) as a lying area. The study confirms earlier suggestions that the amount of space required by EU legislation is insufficient for pigs at the end of the finishing period, even at relatively low temperatures. In situations where the average room temperature exceeds the comfort zone, pigs need additional space to cope with their housing system, or alternative methods to cool themselves down. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Commercial finishing pigs are almost exclusively kept in groups, typically at group sizes of up to 20 pigs. It has been
∗ Corresponding author. Tel.: +31 320 293532; fax: +31 320 238050. E-mail address: [email protected] (H.A.M. Spoolder). 0168-1591/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2012.02.010
suggested that keeping them in large groups (50–2000 pigs) has several advantages (e.g. Vermeer and Hoofs, 1994; Wolter and Ellis, 2002), and an increasing number of farmers is moving towards large group housing systems (e.g. Penny, 2000; Honeyman, 2005; EFSA, 2007). The beneficial effects of keeping finishers in large groups may be associated with an increase in available total space, even at a constant individual space allowance. However, we are only
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starting to understand how pigs cope with (a lack of) space available to them in group housing systems. The amount of space required by group housed finishing pigs is determined by a number of factors such as the size of the animal, the social dynamics of the group and the design of the pen. Another aspect known to affect space requirement is ambient temperature. Pigs are unable to sweat (Ingram, 1965) and rely to a large extent on behavioural measures to lose excess heat. With increasing temperatures they will reduce their general level of activity, reduce feed intake, minimise physical contact with other pigs, prefer to lie and wallow in wet parts of the pen (e.g. the dunging area) and lie laterally to increase surface contact with the floor (SVC report, 1997; Huynh et al., 2005). Most of the behavioural responses are related to qualitative or quantitative aspects of floor space: group housed pigs cope with increasing temperatures by using more space. Although space requirements of pigs in relation to their body size (and to a lesser extent to group size) have been estimated and empirically verified, a direct relationship between ambient temperature and area occupied by the group has not yet been estimated. In the present paper we aim to determine this relationship in two steps: (a) by modelling the consequences of increased temperatures on behavioural changes and resulting space requirements described in literature, and (b) by using an existing dataset to support or refute the modelling outcomes. 2. Theoretical background 2.1. Determining space requirements Group housed pigs need space to support three main purposes: static space (occupied by the body of the pig), activity space (for, e.g. spatial separation of functions such as feeding and excretion) and social space (for appropriate social behaviour) (Petherick, 1983). It is argued that each of these can be assessed separately, and that their sum equates to the total space requirement for the animal. EFSA (2005) continues Petherick’s (1983) analyses and reviews the three functions in more detail. Activity space and social space are the most difficult two to quantify. In considering activity space, ‘functional areas’ have to be taken into account; that is parts of the pen which are used by the pigs for different purposes (such as sleeping, excretion and feeding). To estimate the required amount for these, EFSA (2005) discusses three main points. Firstly, the amount of space needed per pig should be considered separately for each area. Lying and feeding space can be estimated (see below), but area required for excretion is less easy to quantify (and dependent on, e.g. temperature and group size). Secondly, functional areas can overlap and form a ‘multi-functional area’. For example, in simultaneous feeding systems the lying area will overlap with the feeding area (as these events do not take place at the same time) and similar, but less desirable, overlap of functions may occur when ambient temperatures increase and pigs increasingly lie in the dunging area. Finally it is considered that the size of the group has some effect on the space required for each functional area per pig: the use of the dunging area being the most obvious example of this.
When considering social space, there are two elements to consider: pigs need space to avoid being in constant physical contact (‘personal space’), and pigs also need space to engage in social interactions (e.g. fighting, mounting and expression of appropriate social signals). Neither of these can easily be quantified, although some attempts have been made (e.g. Jensen, 1982; Baxter, 1985; Kay and Spoolder, 1997). For static space requirements it is easier to make a quantitative assessment: the amount of space a body occupies can be measured relatively easily. Factors to take into account for this are the size (weight) of the animal, the posture it assumes and the level of space sharing, e.g. when animals lie on top of each other (huddling) or when they share a common space envelope. Space allowance for pigs is usually expressed as ‘number of square meters per animal’ and the inverse (stocking density) as ‘number of pigs per square meter’. However, these units of measure are meaningless without taking the age or weight of the animals into account. Petherick (1983) proposed a method to integrate the element of pig size by using a constant (k) linking surface area (A, in m2 ) to the weight of the animal (W, in kg) through the equation A = kW2/3 . This ‘k-value’ has since been used in several studies on space allowance (e.g. Kornegay and Notter, 1984; Edwards et al., 1988; Gonyou et al., 2006) because it allows biological relationships to be interpreted irrespective of age and weight of the animals studied. In a first attempt to determine the minimal amount of static space pigs need at different weights, Petherick and Baxter (1981) took images from pigs from above and drew rectangles around the individual animals, the so called ‘pigtographs’. From these graphs they calculated k values for sternally recumbent lying pigs (k = 0.019) and for laterally recumbent lying pigs with legs extended (k = 0.047). The amount of static space for a standing pig equates to that of a sternally recumbent lying pig (Petherick and Baxter, 1981) and the same can be argued for sitting pigs. However, the amount of static space a group of pigs needs is dependent on the frequency of lying behaviour, the postures adopted and the amount of space shared between animals. Ekkel et al. (2003) looked at these aspects in a study on total area use by groups of lying pigs. Their estimate of an average k = 0.033 per pig confirms earlier suggestions by Petherick (1983) that the value is the same as for a ‘half recumbent’ lying animal. 2.2. Effects of temperature on pig behaviour As previously indicated, an important external factor affecting the k value is the ambient temperature. Petherick (1983) already noted that temperature affects the amount of floor space pigs use, and Ekkel et al. (2003) stress the fact that their k value only applies to thermoneutral conditions. The effect of temperature on required physical space has not yet been quantified. However, it may be possible to estimate the space requirement indirectly, by investigating the behaviours that groups of pigs express when coping with increasing temperatures. Some of these will have a direct effect on the amount of space used. These are: a) the level of inactivity (as expressed by % of pigs lying),
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Table 1 Literature values for percentage change in behaviours for each degree Centigrade increase in ambient temperature.
Huynh et al. (2005) Aarnink et al. (2006) Pedersen et al. (2003) Ducreux et al. (2002)
Weight range (kg)
Temp range (◦ C)
Lying down
Huddling
Lateral lying
58–65 25–105 60–110 70
16–32 18–28 10–28 18–27
0.2% 0.5% 0.66%
−4.9% −3.7% −1.7%
0.8% 1.9% 1.4% 2.3%
b) the degree of contact or space sharing between animals and c) the change in lying posture, e.g. from lying on the sternum to lying semi-laterally or laterally. There is a limited amount of data in the literature to quantify these three effects. Table 1 presents an overview of some of these data. Activity levels are generally reduced as temperatures increase. This means that more pigs will be lying down. Huynh et al. (2005) estimated that for every degree Centigrade increase in temperature between 16 and 32 ◦ C, the number of pigs lying down increased by 0.2%. One year later, Aarnink et al. (2006) published their finding that this should be around 0.5%. A third estimation can be found in a paper by Pedersen et al. (2003). They found in their study that activity levels in the summer reduced from roughly 20 to 8% when temperature increases from 10 to 28 ◦ C. This could be interpreted as an increase in lying behaviour of 12% over 18 ◦ C temperature difference: so approximately 0.66% per ◦ C. Pigs will reduce physical contact with increasing temperatures. Aarnink et al. (2006) found 3.7% less pigs lying against other pigs for every degree Centigrade increase between 18 and 28 ◦ C. Huynh et al. (2005) estimated that for every degree Centigrade increase in temperature the number of pigs huddling (so in contact with each other) decreased by 4.9%. Finally, Pedersen et al. (2003) estimated a reduction in huddling between 10 and 28 ◦ C from roughly 40 to 8% (in pigs of 60–110 kg), so a reduction of 32% over 18 degrees temperature difference. This equates to 1.7% per ◦ C temperature change. However, it is likely that the decrease was not linear and a faster decrease per degree can be expected in the higher temperature range. The posture of lying pigs changes in response to increased temperatures. Lying laterally increases the contact area of body surface with the floor and promotes the loss of heat, but also increases the amount of floor in use, compared to lying in a sternal (ventral) posture. Ducreux et al. (2002) found a significant increase in lying laterally when comparing pigs kept at 18 ◦ C with 27 ◦ C. At 18 ◦ C they found 66% lying ventrally vs 34% lying laterally. At 27 ◦ C these figures were 44% vs 55% respectively). This means that over 9 ◦ C lateral lying went from 34 to 55% (i.e. 2.3% per ◦ C). In addition, Aarnink et al. (2006) found 1.9% more pigs lying on their sides for every degree Centigrade, and Huynh et al. (2005) estimated this figure to be 0.8%. Based on their observations in insulated buildings, Pedersen et al. (2003) estimated that lying laterally in the summer increased from roughly 40 to 65%, when temperature increased from 10 to 28 ◦ C. This equates to 1.4% per ◦ C. Savary et al. (2009) found that lateral lying increased when temperature increased from 10 to 20 ◦ C for low weight pigs (<50 kg) and from 10 to 15 ◦ C for middle weight pigs (50–80 kg), and then went down again. Heavy
pigs (>80 kg) reduced their lateral lying with increased temperature, from 10 ◦ C up to about 19 ◦ C after which lateral lying increased slightly. It is relevant to note that in this study pigs shifted their preferred lying location from a solid concrete floor to a slatted floor with increasing temperature. In heavy pigs this shift appeared to be the fastest. Another (fourth) way of coping behaviourally with increased temperatures (and which affects the use of space) is the preference to lie in a cool place, as temperature increases. Pigs will move from an insulated (solid, strawed) floor to a wet and colder place. It is likely that this will also affect the amount of space required, as lateral lying is less needed to loose the same amount of heat on slats, compared to a solid floor. Ducreux et al. (2002) found that 70 kg pigs kept at 27 ◦ C preferred to rest on a concrete or slatted floor instead of a solid floor with litter, compared to pigs kept at 18 ◦ C (44% vs 15% respectively). Pedersen et al. (2003) found an increase in lying in the dunging area when temperature rose above 15–20 ◦ C (in pigs of 60–110 kg). Savary et al. (2009) also found that the slatted floor was more frequently used as temperature increased. Based on their data, they estimated a shift from solid to slatted floor occupation from 0 to 20% for <50 kg pigs between 15 and 20 ◦ C, from 0 to 55% for 50–80 kg pigs between 10 and 28 ◦ C, and from 5 to 60% for >80 kg pigs between 12 and 23 ◦ C. Aarnink et al. (2006) found an increase in number of pigs lying on the slatted floor of approximately 10% per ◦ C for 25 and 45 kg pigs and of approximately 5% per ◦ C for 65, 85 and 105 kg pigs. The temperature at which a maximum number of pigs on the slatted floor was reached decreased from 27.5 ◦ C for 25 kg pigs to 23.2 ◦ C for 105 kg pigs. Finally, Huynh et al. (2005) found, for pigs of 62 kg, an increase of lying on the slatted floor of 2.2% per ◦ C at 50% RH and of 2.9% at 65 and 80% RH. The effect of these changes in floor preference on the amount of space required, are difficult to quantify. They are strongly related to the insulating properties of the two floors and other aspects related to the Upper Critical Temperature (UCT) of the pig. The above data allows rough estimates to be made of the effects that an increase of 1 degree Centigrade has on behaviours related to space requirements: between 0.2 and 0.66% extra pigs will lie down, between 1.7 and 4.9% less space sharing will occur and there will be an increase of between 0.8 and 2.3% of lying laterally rather than sternal lying. 2.3. Estimation of k-value at increasing temperatures The effects of the above factors on required space can be modelled. The Ekkel et al. (2003) figure of k = 0.033, determined under thermoneutral conditions, was used as a
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starting point. In this paper, at 21 ◦ C the proportion of lying pigs during the day was approximately 0.8,1 of which a proportion of 0.672 was lying laterally. The area required for sternal and lateral lying is k = 0.019 and 0.047, respectively (Petherick, 1983). There was a proportion of space sharing of 0.132 for all laterally lying pigs (Ekkel et al., 2003) which means that 13.2% of the space occupied by lateral lying was shared, i.e. the space between the extended legs of one pig was occupied by another pig. Estimation of the k value at T = 31 ◦ C equates to a change in temperature of +10 ◦ C, if 21 ◦ C is used as the starting point in the comfort zone of growing pigs of all weights. The effects of this change on space requirement were calculated using the lowest and highest values found in the literature reviewed previously, namely an increase in lying down of 0.2–0.66%, a reduction in space sharing of 1.7–4.9% and an increase in lateral vs sternal lying of 0.8–2.3%. It can be calculated that the effects of a 10 ◦ C increase in temperature, using the highest values reported in the papers above, result in the following predicted proportions of pigs in different postures: Proportion lying pigs: 0.8 + 10 × 0.0066 = 0.866. Proportion lateral lying (of all lying pigs): 0.672 + 10 × 0.023 = 0.902. Proportion of space sharing (of lateral lying pigs): 0.132 − 0.132 × (10 × 0.049) = 0.067. Proportion of lateral lying space which is not shared: 1 − 0.067 = 0.933. From these highest values, a group average k value for lying pigs can be calculated: k for the proportion of lateral lying pigs: 0.902 × 0.047 = 0.0423. Multiply this space for lateral lying pigs by the proportion of unshared space: 0.0423 × 0.933 = 0.0396. k for the proportion of sternal lying pigs: (1 − 0.902) × 0.019 = 0.0019. Average k for all lying pigs (sternal plus lateral): k = 0.0019 + 0.0396 = 0.0414. The average static space required for the whole group can be calculated by multiplying the space for lying pigs by the proportion of lying pigs, and adding the proportion of standing and sitting pigs multiplied by k = 0.019. It follows that k = 0.866 × 0.0414 + 0.134 × 0.019 = 0.0385. This equates to an average space required to support the static body of 0.884 m2 for groups of 110 kg pigs at 31 ◦ C. Conversely, when the lowest values found in the literature are used (increase in lying down: 0.2%; increase in lateral vs sternal lying: 0.8%; reduction in space sharing: 1.7%), it can be calculated that the average k value for lying pigs is 0.0362, and the average k for the whole group
1 At night more pigs were lying, and less activity space was used. For comparison with the empirical data presented later in this paper, we prefer to use Ekkel’s estimate for proportion of pigs lying during the day referred to in his Discussion section.
(lying, sitting and standing pigs) is 0.0331. This equates to 0.760 m2 for a 110 kg pig at 31 ◦ C. The above model calculations are by definition an approximation of what happens to static space requirements when temperature increases. In the second part of this paper an existing dataset was analysed to test the hypothesis that, in a conventional pig building with ample space, the k value will increase with increasing temperature, and the static space requirement at T = 31 ◦ C is between k = 0.0331 and k = 0.0385. 3. Collection and analyses of empirical data The data for this study were obtained from a series of photographs taken from pens in the Comfort Class pig building in Raalte, The Netherlands (De Greef et al., 2011). In this building the behaviour and performance of finishing pigs housed in different group sizes and at different stocking densities was observed from 2006 to 2009. The studies in the Comfort Class system were not designed to investigate the effect of temperature on space use per se, and there are several limitations to the dataset (see below). However, they can provide an interesting cross comparison with data from the literature synthesis presented data above. The stocking density study in the Comfort Class building did not require formal ethical approval from the Animal Experimentation Committee. 3.1. Animals and housing The Comfort Class facility is a naturally ventilated house (30 m × 20 m), with curtains in the side walls above 1.50 m height, regulated by outdoor sensors monitoring wind speed, wind direction and temperature. The building contains three ‘blocks’ of four 30 m2 pens each (Fig. 1). A standard pen measured 3.76 m × 8 m and contained 18 pigs, resulting in an average space allowance of 1.67 m2 per animal. Each pen had three separate functional areas: a kennelled strawed area (3.76 m × 2 m), an open concrete solid-floored lying area (3.76 m × 4 m; not insulated) and a concrete slatted dunging area (3.76 × 2 m). The pigs were kept in these pens from 20 to 100 kg live weight, and were of mixed sex (50% barrows, 50% gilts). They were fed ad libitum from several feed hoppers. At room temperatures above 25 ◦ C water was sprinkled above the slatted floor for 40 s every 30 min. Temperature was monitored and recorded continuously at room level. Above each pen, a colour infrared camera (TeleConnect, model TC516CEXH) was mounted from the roof. The view of each camera covered the full pen except the covered lying area. Each camera took a picture at 15 min intervals throughout the 24 h day. 3.2. Observations on space use The photographs were used to estimate the amount of space used by lying pigs, and to determine the location (kennel, solid floor or slatted floor) of the animals. For the assessment of space occupied, the photographs were projected onto an Excel sheet consisting of square cells (Fig. 2a and b). The dimensions of these square cells
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Fig. 1. Floor plan and cross section of a block of four pens in the Comfort Class building.
could be related to the dimensions of the pen areas on the photograph, and it was estimated that an average square in the solid floor area represented 0.028 m2 . Because of visual distortion a separate value was calculated for the slatted area. For this it was estimated that a square cell represented 0.047 m2 . It is important to note that these two figures represent an average for each of these two areas, which means that the size of a square was overestimated in the middle of the picture and underestimated at the sides. For each photograph, rectangles were fitted around lying pigs (Fig. 2a), similar to the rectangles used by Petherick and Baxter (1981). Standing and sitting pigs were ignored. The photograph was then removed and all square cells in the Excel sheet covered by a rectangle were given the same number. For individual pigs the floor area occupied was calculated as the number of squares in the rectangle multiplied by the area each square represented. Overlapping rectangles were collectively marked as a ‘cluster’, and all square cells in such a cluster were given the same number (Fig. 2b). The area occupied by a cluster was calculated as the number of squares with the same number multiplied by the area a square represented, and divided by the number of pigs in that cluster. Individual pigs or clusters lying in the dunging area were treated separately from pigs lying on the solid floor. Pigs which were entirely or partly in the kennel were assumed to be lying, but not included in the estimations for average space occupation per pig.
Random effects of batch, pen (within batch), date (within pen) and cluster (within date) were included in the mixed model. The space requirement data were considered normally distributed (checked by analyses of residuals). The data structure here was slightly unbalanced because individual pens could have a different number of clusters at the same time (date). For analyzing the proportion of lying animals or the preference of the location, the data structure was reorganised where date (within) pen was the experimental unit. The data of the percentage of lying animals were analysed with a logistic model (Generalized Linear Mixed Model, GenStat, 2002). The preference data were considered as ordinal response data (McCullagh and Nelder, 1989), since the kennel provides the most thermal protection and slatted floor provides the least. The following ordinal response model was used:
3.3. Statistical analyses
Within each series of photographs from one of the ten pens selected, only pictures from days on which the ambient temperature reached 16 ◦ C or more were used. To minimise dependencies between lying patterns, only one
The data analysis was conducted using the statistical programming language Genstat version 8 for Windows.
log it(j (x)) = ˛j − ˇT x, j = 1, . . . , K − 1
(1.2)
With k − 1 intercept terms or cut-off points (˛j ), were k (number of classes) is 3, ˇT x is a short notation of the model terms in model 1.1, and is the cumulative probability for category j. 4. Results of empirical study 4.1. Useable photographs
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Fig. 2. (a and b) Illustration of the way the area used by the lying animals was recorded.
picture per day per pen was analysed. The warmest part of the day was chosen from which to select a picture. A total of 276 photographs were thus selected for further analyses, from 4 batches. The groups in batches 1–3 were followed from December 2006 to December 2007, and in batch 4 during the summer of 2009 (Table 2). The temperature during the observation periods ranged from 16 to 32 ◦ C. Almost all pictures used (268 out of 276) were taken between 12:00 and 18:00 h, with an ‘average time’ of 15:15 h. The number of photographs taken during higher ambient temperatures was relatively low, but the observations were relatively evenly distributed over the total growing-finishing period (Table 3).
Table 2 Description of batches of pigs used in the study. Dates Batch 1 Batch 2 Batch 3 Batch 4
15 December 06–3 April 07 12 April 07–16 July 07 7 August 07–10 December 07 12 May 09–18 August 09
Temp range (◦ C) 16.1–19.4 16.3–31.9 16.2–26.0 16.0–27.8
Av temp 17.6 25.2 18.9 21.6
4.2. Standing behaviour and distribution of pigs in the pen The posture of the visible pigs was affected by temperature: pigs were standing less with increasing temperature
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Table 3 Number of photographs analysed per temperature category and weight category. Temperaturea 16
18
20
22
24
26
28
30
20–40 kg 40–60 kg 60–80 kg 80–100 kg 100+ kg
8 20 21 20 0
0 4 15 18 3
4 24 10 10 5
4 4 7 10 4
5 10 9 9 1
0 2 7 1 3
2 1 8 7 6
6 0 7 0 1
29 65 84 75 23
Total
69
40
53
29
34
13
24
14
276
Temperature truncated to 2 ◦ C categories: 16 ◦ C means all temperatures between 16 and 18 ◦ C.
70 60
% of pigs
(P = 0.007, F = 7.28, df = 298) (Fig. 3). The line of best fit was linear and equated the percentage of non-lying pigs to 24.337 − 0.5815 × T (in ◦ C). This suggests that for every degree increase in temperature, the number of non-lying pigs decreases by 0.58%, (or an increase of lying pigs (visible and in the kennel) of 0.58%). The number of pigs lying in different areas of the pen changed with increasing temperature as well as with increasing pig weight (P < 0.001). There was no interaction between these two factors (F = 2.36, df = 212, P = 0.126). The location preference of the animals was modelled using an ordinal response model (corrected for batch and pen). As body weight increased, pigs were observed less in the kennel and more on the slatted area. An increase in ambient temperature had a similar effect (Fig. 4). At low temperatures the kennel and the solid floor were predominantly used when lying, and hardly any pigs lay on the slatted floor. At high temperatures the slats were increasingly preferred, at the expense of the solid floor and the kennelled area. The average increase per degree Centigrade was 1.39% (calculated as the average percentage on the slatted floor at 30 ◦ C, minus the average at 16 ◦ C, and divided by 14 degrees).
50 40 30 20 10 0 16
18
20
22
24
26
28
30
16
18
20
22
24
26
28
30
16
18
20
22
24
26
28
30
70 60
% of pigs
a
Total
50 40 30 20 10 0
70
Over the full temperature range of 16–32 ◦ C, the model which described the relationship between the floor area occupied by lying pigs and the two factors Weight and
% of pigs
60
4.3. Floor area occupation by lying pigs
50 40 30 20 10
% standing + sitting pigs
0 25
Temp 20 Fig. 4. Preferred location for pigs at different temperatures (modelled), top: 25 kg, middle: 65 kg, bottom: 105 kg body weight. Thin solid lines represent lying in the kennelled area, thick solid lines are the solid lying area, dashed lines the slatted dunging area.
15 10 5
Temp was:
0 15
20
25
30
35
Temp Fig. 3. The percentages of standing or sitting pigs in relation to ambient temperature (out of a total of 18 pigs per pen, with all pigs in the kennel assumed to be lying).
Ln (Area) = −0.6064 + 0.0044 × Temp + 0.6832 Weight (2.1) In this model, both ambient temperature and body weight were standardised so that model estimates were
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calculated within the range of observations. The intercepts were set at T = 20 ◦ C, and weight = 65 kg (and not at 0 ◦ C and 0 kg respectively), therefore: Temp = ambient temperature minus 20 ◦ C. Weight = Ln (body weight/65 kg). The amount of floor space a pig uses to lie on increased with increasing body weight (P < 0.001), as well as with increasing ambient temperature (P < 0.05). There was no interactive effect (P = 0.12) between these two factors on floor surface used. 4.4. k-Value estimation The observations on lying space occupation in relation to temperature and weight can be used to estimate k values, which link lying area to temperature, irrespective of the pig’s weight. Therefore the relationship (model 2.1 above) between the floor area occupied and the two factors Weight and Temp can be rewritten into a calculation for the k value. Area = (e−0.6064 ) × (1/65)
0.6832
× e0.0044×Temp
× (body weight)0.6832
(2.2)
Or : Area = k-value (varying by temp) × (body weight)0.6832
(2.3)
It is interesting to note that the conversion from the three (weight) to two (area) dimensions of a pig body in our estimated model (2.3) equals 0.6832. This is very close, but different, to the theoretically correct value of 2/3 (i.e. 0.6667). It is likely that small errors, e.g. due to parallax effects in the observations are to blame for this. If we correct for this, back to the value of 2/3, we find k-value = (e−0.6054 ) × (1/65)
2/3
× e0.0044×Temp
(2.4)
The modelled best fit through the k-values for all lying pigs associated with temperatures increasing from 16 to 31 degrees (averaged at 1 ◦ C increments), suggests a k-value of k = 0.0350 at T = 31 ◦ C (Fig. 5).
0.039
K-value
0.037 0.035 0.033 0.031 0.029 0.027 0.025 15
20
25
30
Temp (averaged per 1 oC) Fig. 5. k-Value for lying pigs in relation to ambient temperature between 16 and 31 ◦ C (averaged per 1 ◦ C). Superimposed on these data is the modelled k value (increasing with temperature).
Estimation of the group mean k value for static space (body space when lying, sitting or standing) requires information on the proportion of lying pigs. This can be estimated from the equation in paragraph 4.2 above: 24.337 − 0.5815 × T (in ◦ C). At 31 ◦ C this is 6.31%. That means that a proportion of 0.063 of the pigs is standing, and therefore 0.937 is lying. Using the values from our empirical dataset, the group mean k-value for static space requirement at 31 ◦ C is: 0.937 × 0.0350 + 0.063 × 0.019 = 0.0339, equivalent to 0.78 m2 for a 110 kg pig. 5. Discussion Groups of finishing pigs cope with increasing temperatures by changing their behaviour. Some of these changes require additional ‘static’ space (the space physically occupied by the body of a pig). There are limited data available in the literature to quantify the effects of temperature on static space requirements. In this paper we present some data from peer reviewed publications and estimate that the k value at 31 ◦ C will be between k = 0.0362 and 0.0414 for all lying pigs, and between k = 0.0331 and 0.0385 for mean static space requirement of all pigs in the group. The present paper then proceeds to study actual changes in space required, in an ongoing study of group-housed finishing pigs. These empirical data suggest a k value for all lying pigs of k = 0.0350, and for total static space of k = 0.0339. This means that for static (body) space alone, at 31 ◦ C, a 110 kg pig will need on average 0.78 m2 . The estimated k value based on the pig study (0.0339) is at the lower end of the data modelled on the basis of studies in the literature (range 0.0331–0.0385). It appears that the pigs in the Comfort Class system are able to cope with increasing temperatures by using up less additional space, compared with the theoretically derived space requirements of pigs in other studies. There are several possible explanations for this, related to the design of the building. First of all, the Comfort Class system has three different functional areas: the kennel, a solid (lightly strawed) open lying area and a slatted dunging area. The pigs in this study responded to increasing temperatures not just by increasing the space they occupied, but also by moving to cooler parts of the pen: from the kennel to the solid floor, and from the solid floor to the slats. This behaviour is consistent with that observed in other studies (e.g. Ducreux et al., 2002; Aarnink et al., 2006; Savary et al., 2009; Hillmann et al., 2004). Initially this may have resulted in a slight increase in lying space required: Hillmann et al. (2004) suggested that, with increasing temperatures, pigs will stop huddling first (i.e. increase lying without contact), before increasing their lying behaviour in the dunging area. They did not study the lying posture, but it seems likely that the shift to lying in the dunging area does not immediately result in an increased space requirement, as pigs will initially lie in a sternal position. A meta-analysis of existing data by Averos et al. (2010) also suggests that pigs on a slatted floor use less lying space compared to pigs on a solid floor, in otherwise comparable circumstances. It is relevant to note that from a hygiene point of view the increased lying behaviour in the dunging area has negative consequences for the performance
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of the system as a whole: pigs will increasingly use the solid floor as dunging area, resulting in dirtier pigs and pens. A second factor which will have affected the amount of space the pigs used is the showering system which was activated at temperatures above 25 ◦ C. Pigs which moved to the slatted floor generally had only one behavioural way to cope with a further increase in temperature, which was to increase the contact between body and floor by lying laterally. The showering system will have slowed down the change to lateral lying, although this is still likely to have increased as temperature went up. Virtually all pictures used were taken between 12:00 and 18:00 h, since this is when the highest ambient temperatures occur in practice, and therefore reflect the afternoon behaviour of ad libitum fed finishing pigs. It can be argued that the samples therefore do not represent the ‘average’ space required by the animals during the 24 h day. The ‘group k-value for static space’ depends on the proportion of pigs lying, and will be higher if all pigs lie down (providing a fixed proportion of all lying pigs lies laterally, as sternal lying requires an equal amount of space as standing). Although the present paper did not investigate the effect of time, it is known from other studies (e.g. Ekkel et al., 2003) that the afternoon time frame provides a good representation of the lying behaviour during the day in ad lib. fed finishers. However, at night, pigs will decrease activity levels and lie down more. This means that the empirical data in the present study are an underestimation of the average lying space required during the 24 h day, particularly if high temperatures persist into the night. If activity space or total space is considered, the prediction of space required gets more complex. EFSA argues that being active (other than simply standing) requires at least twice the k value for a standing pig (so 2 × 0.019 = 0.038). This of course is only an estimate, but is higher than the average lying space required (k = 0.033), although still lower than the space required for lateral recumbent lying (k = 0.047) which is the predominant posture at night (Ekkel et al., 2003). Therefore, it can be hypothesised that the afternoon data used in the empirical part of this study provides an underestimate of lying space requirement, as well as an underestimate of static + activity space required, over the 24 h day. The amount of space currently offered in pig buildings depends on legislative and economic factors. In the EU the minimum space allowance is prescribed in EU Directive 91/630/EC, and approximately equates to k = 0.030 (Spoolder et al., 2000). This k-value matches results from earlier work in which an economic optimum was calculated, based on pig growth and feed efficiency at different space allowances, and the associated investment and maintenance costs for the accommodation (Edwards et al., 1988). The EC legislation makes it compulsory for pigs in the weight category of 85–110 kg to be kept at a minimum of 0.65 m2 per individual. Intensively housed finishing pigs are generally kept in the same pen for the whole of the finishing period (from roughly 30 to 110 kg live weight), and thus at 0.65 m2 . To estimate if this is sufficient to accommodate the body dimensions of the pig (static space) as well as activities such as feeding and
237
eliminating in a separate dunging area (activity space), further development of the model is needed. From the theoretical background it is clear that the amount of static space only relates to the physical dimensions of the body of the animals in the group, as affected by posture and level of space sharing. In addition to this, activity space and social space should be taken into account when calculating the total amount of space required (Petherick, 1983). These two components are very hard to estimate. For social space the amount required is very much dependent on the circumstances, as social activities are unevenly distributed in time and space. Play behaviour decreases as pigs get older and aggressive behaviour is either related to the group’s social stability or to competition for access to resources. However, EFSA (2005) did attempt to quantify activity space under thermoneutral conditions. Starting from k = 0.033 (Ekkel et al., 2003), they argued that for active pigs (approximately 20%) the k value can be estimated to be 2 × 0.019 = 0.038. This means that they added an area equivalent to a standing pig for every sitting or standing animal. This space would then be available for the active animal to walk, explore, root, etc. EFSA also considered dunging and feeding behaviour. They assumed that for a group of ten pigs one extra pig space (k = 0.019) is required to separate the dunging area from lying and activity area (so k = 0.0019 per animal). However, EFSA (2005) did not add additional feeding space to their estimates for k, as space required for feeding can be substituted for activity space (when pigs feed consecutively) or static (lying) space (when pigs feed simultaneously). These estimates relating to activity space can be interpreted in relation to increased temperature by taking into account the proportion of active pigs. In the group housing system studied in this paper, this proportion of active pigs was estimated to be 0.063 at 31 ◦ C. EFSA (2005) suggests these pigs should have twice the amount of static space (k = 0.038), and for every pig a tenth of the space for a standing pig should be added to provide a separate dunging area (k = 0.0019). Therefore, for the groups studied in the Comfort Class pig building, the k-value for static + active space at 31 ◦ C is: 0.937 × 0.0350 + 0.063 × 0.038 + 0.0019 = 0.0371, equivalent to 0.85 m2 for a 110 kg pig. The predicted effects of temperature at different bodyweights on the amount of physical (static) space pigs plus activity space that pigs need, can be compared to the current EU legislation (Fig. 6). The predictions are based on the empirical data in this paper, and the model derived from them. The data suggests that if the legal minimum is applied, pigs heavier than 85 kg are all housed at stocking densities which are too high. Fig. 6 also suggests that the effects of temperature are relatively modest. However, the effects of temperature in this dataset were mitigated by the circumstances under which the animals were kept. They were housed in a naturally ventilated building, had access to different functional areas and at temperatures over 25 ◦ C a showering system was triggered. For conventional group housing systems, it is likely that the increase in space required to cope with increasing temperatures is closer to the upper end of the
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0.9
Area (m2)
0.8 0.7
105 kg
0.6
85 kg
0.5
65 kg
0.4
45 kg
0.3
25 kg
0.2
A=0.65m2
0.1 0 16
19
22
25
28
31
o
Temp ( C) Fig. 6. Modelled estimates of the amount of static space plus activity space required for pigs at different weights, and at increasing temperatures, in relation to common European practice of A = 0.65 m2 .
range identified from literature, than the modelled data from the Comfort Class. 6. Conclusion It can be concluded from this study that the amount of space pigs require to cope behaviourally is affected significantly by increasing temperatures. In addition, the study confirms earlier suggestions that the amount of space required by EU legislation is insufficient for pigs at the end of the finishing period, even at relatively low temperatures. In situations where the average room temperature exceeds those in the comfort zone, pigs need additional space to cope with their housing system, or alternative methods to cool themselves down. Conflict of interest None. Acknowledgments The authors want to thank Agnes de Wit for her help in analysing the data. We gratefully acknowledge the financial support for this project by the Dutch Ministry of Agriculture, Nature Management and Food Quality. For her part in this study, SAE would like to thank the European Community for their financial contribution via the Sixth Framework Programme’s Integrated Project QPORKCHAINS (FOOD-CT-2007-036245). References Aarnink, A.J.A., Schrama, J.W., Heetkamp, M.J.W., Stefanowska, J., Huynh, T.T.T., 2006. Temperature and body weight affect fouling of pig pens. Journal of Animal Science 84, 2224–2231. Averos, X., Brossard, L., Dourmad, J.Y., De Greef, K.H., Edge, H.L., Edwards, S.A., Meunier-Salaun, M.C., 2010. Quantitative assessment of the effects of space allowance, group size and floor characteristics on the lying behaviour of growing-finishing pigs. Animal 4 (5), 777–783. Baxter, M., 1985. Social space requirements of pigs. In: Zayan, R. (Ed.), Social Space for Domestic Animals. Martinus Nijhoff Publishers, Dordrecht, The Netherlands, pp. 116–127. De Greef, K.H., Vermeer, H.M., Houwers, H.W.J., Bos, A.P., 2011. Proof of Principle of the Comfort Class concept in pigs – experimenting in the midst of a stakeholder process on pig welfare. Livestock Science 139, 172–185.
Ducreux, E., Aloui, B., Robin, P., Dourmad, J.-Y., Courboulay, V., MeunierSalaün, M.-C., 2002. Ambient temperature influences the choice made by pigs for certain types of floor. Journées de la Recherche Porcine 34, 211–216. Ekkel, E.D., Spoolder, H.A.M., Hulsegge, I., Hopster, H., 2003. Lying characteristics as determinants for space requirements in pigs. Applied Animal Behaviour Science 80, 19–30. EC, 1991. Council Directive 91/630/EC of 19 November 1991 laying down minimum standards for the protection of pigs (OJ L 340,11.12.1991, p. 33). Edwards, S.A., Armsby, A.W., Spechter, H.H., 1988. Effects of floor area allowance on performance of growing pigs kept on fully-slatted floors. Animal Production 46, 453–459. EFSA, 2005. The welfare of weaners and rearing pigs: effects of different space allowances and floor types. The EFSA Journal (2005) 268, 1–19. EFSA, 2007. Animal health and welfare in fattening pigs in relation to housing and husbandry. The EFSA Journal (2007) 564, 1–14. GenStat, 2002. Reference Manual, Release 6.1. VSN International, Oxford, UK. Gonyou, H.W., Brumm, M.C., Bush, E., Davies, P., Deen, J., Edwards, S.A., Fangman, T., McGlone, J.J., Meunier-Salaun, M.-C., Morrison, R.B., Spoolder, H., Sundberg, P.L., Johnson, A.K., 2006. Application of broken line analysis to assess floor requirements of nursery and growerfinisher pigs expressed on an allometric basis. Journal of Animal Science 84, 229–235. Hillmann, E., Mayer, C., Schrader, 2004. Lying behaviour and adrenocortical reactions as indicators for the thermal tolerance of pigs of different weight. Animal Welfare 13, 329–335. Honeyman, M.S., 2005. Extensive bedded indoor and outdoor pig production systems in USA: current trends and effects on animal care and product quality. Livestock Production Science 94 (June (1–2)), 15–24. Huynh, T.T.T., Aarnink, A.J.A., Gerrits, W.J.J., Heetkamp, M.J.H., Canh, T.T., Spoolder, H.A.M., Kemp, B., Verstegen, M.W.A., 2005. Thermal behaviour of growing pigs in response to high temperature and humidity. Applied Animal Behaviour Science 91, 1–16. Ingram, D.L., 1965. The effect of humidity on temperature regulation and cutaneous water loss in young pigs. Research in Veterinary Science 6, 9–17. Jensen, P., 1982. An analysis of agonistic interaction patterns in grouphoused dry sows – aggression regulation through an ‘avoidance order’. Applied Animal Ethology 9, 47–61. Kay, R.M., Spoolder, H.A.M., 1997. Improving the welfare of newly weaned sows by minimising aggression during mixing. Study 1: the effect of flight distance on aggression and skin damage. MAFF report, ADAS Terrington. Kornegay, E.T., Notter, D.R., 1984. Effects of floor space and number of pigs per pen on performance. Pig News and Information 5 (1), 23–33. McCullagh, P., Nelder, J.A., 1989. Generalized Linear Models, 2nd ed. Chapman & Hall/CRC, Boca Raton, Florida. Pedersen, S., Sousa, P., Andersen, L., Jensen, K.H., 2003. Thermoregulatory behaviour of growing-finishing pigs with access to outdoor areas. In: Agricultural Engineering International, CIGR, Manuscript BC 03 002, p. 16. Penny, P.C., 2000. Effect of modification to pen design formations on the performance of weaned pigs housed in large group systems. Journal of Animal Science 78 (Suppl. 1), 238.
H.A.M. Spoolder et al. / Applied Animal Behaviour Science 138 (2012) 229–239 Petherick, J.C., 1983. A biological basis for the design of space in livestock housing. In: Baxter, S.H., Baxter, M.R., MacCormack, J.A.C. (Eds.), Farm Animal Housing and Welfare. Martinus Nijhoff Publishers, Dordrecht, pp. 103–120. Petherick, J.C., Baxter, S.H., 1981. Modelling the static spatial requirements of livestock. In: MacCormak, J.A.D. (Ed.), Modelling, Design and Evaluation of Agricultural Buildings. CIGR Section II Seminar, Scottish Farm Buildings Investigation Unit. Bucksburn, Aberdeen, pp. 75–82. Savary, P., Gygax, L., Wechsler, B., Hauser, R., 2009. Effect of a synthetic plate in the lying area on lying behaviour, degree of fouling and skin lesions at the leg joints of finishing pigs. Applied Animal Behaviour Science 118, 20–27.
239
Spoolder, H.A.M., Edwards, S.A., Corning, S., 2000. Legislative methods for specifying stocking density and consequences for the welfare of finishing pigs. Livestock Production Science 64, 167–173. SVC, 1997. The Welfare of Intensively Kept Pigs – Report of the Scientific Veterinary Committee, adopted 30 September 1997, website: http://europa.eu.int/comm/food/fs/sc/oldcomm4/out17 en.html. Vermeer, H.M., Hoofs, A.I.J., 1994. The effect of weaner group size on performance and profitability. Praktijkonderzoek Varkenshouderij, proefverslag nummer P1.118, pp. 5–6. Wolter, B.F., Ellis, M., 2002. Impact of large group sizes on growth performance in pigs in the USA. Pig News and Information 23, 17N–20N.