Ad libitum feeding of sows with whole crop maize silage—Effects on slurry parameters, technology and floor pollution

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Ad libitum feeding of sows with whole crop maize silage—Effects on slurry parameters, technology and floor pollution Peter Ebertza,*, Alexander J. Schmithausena,b, Wolfgang Büschera a b

Institute of Agricultural Engineering, University of Bonn, 53115 Bonn, Germany Corteva Agriscience™ the Agriculture Division of DowDuPont™, 81677 München, Germany

A R T IC LE I N F O

ABS TRA CT

Keywords: Gestating sows Pregnant sows Input-output Manure-management Polluted surface areas of barns Hygiene of slatted floor

The advantages of ad libitum feeding of sows with diets rich in crude fibre on reduced stereotypies and improved saturation are well known. Less well known are the consequences of such feeding on the resulting amount of slurry and pollution of the pen floor area, which are the objectives of the present study. During a 40-day trial, 20 sows were fed ad libitum with a diet rich in crude fibre, based on maize silage (MS trial). Compared to the restricted control feeding (CON trial), there was 1.6 times more slurry, and the slurry quality differed. The reduced dry matter content in the MS trial caused more smeared slots in the slatted floor, and the increased excrements produced poor floor cleanliness in comparison to the CON trial. Thus, animals in the MS trial were quieter and fully occupied, indicating an improvement in animal welfare but it was also worsened, due to the higher level of floor pollution relative to the CON trial. Besides, the farmrelated environment is affected by the increased amount of feed and consequent tying-up of resources, as well as by the amplification of produced excrements that in turn must be stored and spread over sufficient available arable land.

1. Introduction Restrictive feeding of pregnant sows is common practice in modern housing systems. The feeding of highly concentrated diets results in long periods of inactivity and constant hunger, which leads to abnormal behaviour in pigs (Barnett et al., 2001). Hunger and frustration increase the aggression level and competition for feed, in group housing systems (Meunier-Salaün et al., 2001). It also results in stereotypies without an obvious function, such as biting and chewing (Bergeron et al., 2000). Stereotypies can be an indicator for reduced animal welfare (Brouns et al., 1994). Roughage-based diets reduce these problems, by decreasing hunger and extending the daily time of feed intake (Bergeron et al., 2000; Brouns et al., 1994; Jeroch et al., 2008). By feeding sows with high-fibre diets, the resting time is increased, and the frequency of abnormal behaviour is lowered (Robert et al., 1993). When used as the fibre source, silages can reduce the need for concentrates in the feeding of pregnant sows (Schulz et al., 2018). However, these positive effects of fibrous feed on a higher degree of satiety (Danielsen and Vestergaard, 2001) influence the resulting amount (Massé et al., 2003; Sievers and Kamphues, 2017) and composition of pregnant sows excrements (Canh, 1998; Hansen et al., 2007; Kleine, 2012; Preißinger et al., 2016) or slurry (Massé et al., 2003; Philippe et al., 2015), in housing systems with slatted floors. A broader context of high-fibre diets must observe the impact on slurry quality, storage, handling and land application

Abbreviations: MS, maize silage; CON, control feeding ⁎ Corresponding author at: Institute of Agricultural Engineering, University of Bonn, Nussallee 5, 53115 Bonn, Germany. E-mail address: [email protected] (P. Ebertz). https://doi.org/10.1016/j.anifeedsci.2019.114368 Received 21 February 2019; Received in revised form 24 October 2019; Accepted 9 December 2019 0377-8401/ © 2019 Elsevier B.V. All rights reserved.

Please cite this article as: Peter Ebertz, Alexander J. Schmithausen and Wolfgang Büscher, Animal Feed Science and Technology, https://doi.org/10.1016/j.anifeedsci.2019.114368

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Fig. 1. Details of experimental barn section and used barn equipment in the trials: fully slatted floor (20 mm slot width), feeding system: Quickfeeder, 1× concentrated feed per day, water ad libitum via aqua level sensor and nipple drinkers; automatic feeder for maize silage (MS) (only in the MS trial).

practices (Massé et al., 2003). The quality or composition of the excrements and slurry, which, among other things, is due to feeding, is also important for the cleanliness of the barn floor (Plonait, 2004). Polluted barn floors should not contain large amounts of excrements, as they present a risk of slipping for animals and humans (Warzecha, 2006). In addition, wet and polluted barn floors pose an increased risk for claw diseases (Wiedmann et al., 2011). Therefore, the present study conducted a ‘before and after’ comparison in pregnant sows not in laboratory, but under real practical conditions. First, the input and output were evaluated by pre-sampling of feed and water (‘before’) and post-analysis of the excrements (‘after’). Secondly, the technical challenges in ad libitum feeding of whole crop maize silage (MS) were discussed, and the polluted surface area was validated. 2. Materials and methods 2.1. Animals and housing The study was implemented under practical conditions in a gestation barn of an agricultural farm (135 productive sows; Rhineland-Palatinate, Germany), with 20 sows of the German Landrace (Lactation Nos.: 2–6, 230 ± 28 kg body weight [BW]). The used barn (53 m²) consisted of three group pens (3.2 × 5.1 m or 2.8 × 5.1 m) for 7 or 6 sows each (Fig. 1). Water was continuously available for ad libitum intake either viaaqua level sensor in feeding trough (Fig. 2) or one nipple drinker per pen.

Fig. 2. A) Specially converted automatic feeder for maize silage: equipped with stirring rods and a larger tube diameter compared to a standard automatic feeder. B) ‘Quickfeeder’ technique for feeding the farm usual concentrated diet. C) Aqua level sensor in feeding trough. D) Functionality of the aqua level sensor: The drinker is a water valve that adjusts a constant water level in troughs (POLnet, 2019). 2

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Table 1 Ingredients and complete chemical composition of used diets. In the further course of this manuscript, it was focussed on the silage and fibre contents. Ingredients (g kg−1)

MS trial

CON trial

Concentrated feed 2.57 kg sow−1 day−1

+ MS ad libitum

Concentrated feed 2.57 kg sow−1 day−1

Barley a Wheat a Soybean meal a Soybean oil a Formic acid a Mineral mix a Milled maize silage

300 470 190 3 2 35 –

– – – – – – 1000

300 470 190 3 2 35 –

Chemical composition DM b (%) crude protein (g kg−1 DM b) crude ash (g kg−1 DM b) crude fibre (g kg−1 DM b) Ca (g kg−1 DM b) Mg (g kg−1 DM b) P (g kg−1 DM b)

88.2 213.0 62.7 35.6 11.60 2.88 5.54

41.1 71.5 27.3 141.0 1.91 0.99 2.26

88.2 213.0 62.7 35.6 11.60 2.88 5.54

a b

Milled and mixed with other listed ingredients. DM, dry matter.

2.2. Preliminary test: feeding and experimental set-up In a preliminary test of 20 days (d) (29.02.2016–19.03.2016), 18 sows (3 × 6) were offered different forages (MS, whole crop wheat silage, sugar beet pulp) every day at 18:00 h, as optional feed, additional to the usual farm amount of concentrated feed (2.57 kg sow−1 d−1), fed in the morning. This trial setting was chosen in order to find out which silage type is preferred by the sows and will probably produce the highest amount of slurry later in the main experiment (worst case scenario). The three silages were weighed and randomly distributed at two feeding places in each trough (cf. Fig. 1). Within 3 h, silage was constantly refilled, providing the trough was emptied by the sows, similar to the preference test at Gerlach et al. (2014). The leftover silage was reweighed. Each batch was oven-dried at 105 °C for 24 h, so that the intake of DM between silages could be compared. Experimental design is summarised in Table 2. Based on the results achieved, MS was used as feed for the following trials (see results section).

2.3. Main experiment: feeding and experimental set-up The whole experimental period lasted 80 d (11.04.2016–03.07.2016) and was divided into two periods. Each period started 3 d after adaption feeding where the sows were fed a ration of concentrated feed, based on farm-owned corn and soybean meal (Table 1). During the first period (40 d), the sows were offered the usual farm amount (2.57 kg sow-1d−1) of concentrated feed and, additionally, milled MS for ad libitum intake (MS diet, ‘maize ad libitum feeding trial’) (Tables 1 and 2). Adaption feeding occurred in another comparable compartment not to influence the slurry data of the following control trial. Then, the new sow groups were introduced into the experimental compartment. Period two (40 d) started immediately after the first period and is defined as control feeding (CON trial, ‘restricted feeding trial’). In CON trial, the sows were only fed with the usual farm amount (2.57 kg sow−1 d−1) of concentrated feed (Tables 1 and 2). Adaption feeding occurred here as well as above in another comparable compartment not to influence the slurry data. The ambient conditions within the compartment were slightly different during the experimental period: the temperature and relative humidity (RH) were 20.6 °C and 55.5 % RH, and 21.6 °C and 60.4 % RH, in the MS trial and CON trial, respectively (Table 2). The data were monitored by using a Testo 174H data logger (Testo SE & Co. KGaA, Lenzkirch, Germany). For feeding the dry concentrated feed, a technique like the ‘Quickfeeder’ (Hoy and Bauer, 2003) was used in both periods (Fig. 2). The Quickfeeder is a feeding system with a long trough along the wall. At the through, feeding places with a width of around 0.5 m are positioned, restricted by side-walls between every feeding place. An auger-linked dispenser with a down-pipe integrated in the side-wall is placed above the trough in the middle between two feeding places (Hoy and Bauer, 2003). Feeding the concentrated feed took place once daily at 08:00 h, and MS (only during MS trial) was refilled at the same time for ad libitum intake. In both periods (MS and CON trial), water consumption was recorded daily at 07:50 h, from a mechanical water meter. The MS was weighed daily into specially converted automatic feeders (Figs. 1 and 2). To ensure that the MS (mean 41 % dry matter [DM]) ran automatically and did not block the feeders, it was additionally milled after harvesting, with a Corn-Cob-Mix mill (Type Willemsen FF9W/K, Chr. Willemsen GmbH, Stadtlohn, Germany). Retention samples (200 mL) of the daily weighed amount of MS were frozen. After the experimental period, all samples were thawed, and DM was determined by drying the samples at 105 °C for 24 h. 3

4

24.05.2016–03.07.2016

CON trial

Dry matter.

29.02.2016–19.03.2016 11.04.2016–21.05.2016

Preliminary test MS trial

a

Time of measurement period

Trial

40

20 40

Duration (days)

21.6 ± 1.8 °C 60.4 ± 6.0 % RH

17.7 ± 1.2 °C 58.5 ± 3.7 % RH 20.6 ± 3.4 °C 55.5 ± 8.1 % RH

Barn temperature and relative air humidity (RH)

Table 2 Experimental design. Period, duration, barn temperature/barn air humidity and examined parameters.

Preference test: amounts and DMa of consumed silage types INPUT: amounts and DMa of Water + Feed. OUTPUT: amounts and DM a of slurry + floating layer. Validation of polluted pen area. INPUT: amounts and DMa of Water + Feed. OUTPUT: amounts and DMa of slurry + floating layer. Validation of polluted pen area.

Examined parameters

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Fig. 3. Exemplary representation of the degrees of pollution: A) Dry/clean surface area. B) Wet surface area. C) Polluted surface area. D) Wet and polluted surface area.

2.4. Sampling of slurry Before the main experiment, the compartment was cleaned, farm-usual, with a high-pressure cleaner. Between the two trials, the compartment was not cleaned, to avoid the cleaning water entering the slurry since this could affect the data. After every trial, the animals were removed from the compartment, and the amount of slurry was detected. The first step was to determine the height from the ground to the floating layer and the thickness of the upper floating layer, by using a measuring tape. The surface area of the slurry channel was measured (two separated channels, 15.3 and 21.2 m², respectively), and the volume of the slurry was calculated by measuring the filling level, as described at Bohnenkemper and Steffens (2006). Samples were collected from the floating layer, liquid manure and, after homogenisation, from the mixed slurry, and oven-dried at 105 °C for 24 h for DM measurements. Before and after each trial, the slurry channels were emptied up to a technical residue, which was quantified via the filling level. Additionally, the technical DM residue was ascertained. 2.5. Determination of the polluted surface area To determine faecal pollution of the slatted floor, the whole pen area of 45 m² was divided into score-squares and assessed by the same method as described at Ebertz et al. (2019). Each score-square in this study was approximately 0.8 m × 0.8 m, depending on pen size. The squares were assessed every day at 18:00 h. The pollution was differentiated into the pollution of the surface area (1 = green = dry/clean; 2 = yellow = wet; 3 = orange = polluted; 4 = red = wet and polluted, see examplary pollutions also Fig. 3) and the percentage of occluded slots in the slatted floor (a = no stroke = 0–25 % closed; b = one stroke = 26–50 % closed; c = two strokes = 51–75 % closed; d = three strokes = 76–100 % closed). 2.6. Statistical analysis and graphical presentation Data were statistically analysed using SPSS Statistics 24.0 (IBM, New York, USA). The descriptive statistics involved the metrics of sample size, mean value, standard deviation, minimum and maximum. The tests were conducted on normally distributed data, using the Kolmogorov–Smirnov test, at relevant points. When there was no normal distribution, the Kruskal–Wallis test was chosen, to determine significant differences. All tests were conducted at p = 0.05. In order to better distinguish minor differences between the variants optically, the surface area pollution was not represented by a linear but by a disproportionate labeling of the y-axis in Fig. 4(B). Marking distances in the lower percentage range smaller than in the upper. 3. Results 3.1. Preliminary test data To clarify which whole plant silage is preferred by the sows and which will probably lead to the highest amount of slurry in the main trial, a preference experiment was performed as the preliminary test. From Table 3, it was evident that the MS (854 g DM sow−1 d−1) was significantly preferred over the whole crop wheat silage (165 g DM sow−1 d−1) and sugar beet pulp (37 g DM sow−1 d−1), by sows (n = 18 in preliminary test). All sows ate large quantities of MS. Individual animal-specific differences were evident in the intake of whole crop wheat silage and even more for sugar beet pulp. One sow in pen 3 preferred notable amounts of sugar beet pulp in comparison to the remaining sows. To test the ‘worst case’ of technical challenges, MS was chosen since these results ensured the maximum feed intake and, thus, probably the highest amount of slurry produced by the animals. 5

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Table 3 Preliminary test: preference of silage type by 18 pregnant sows. Silage type

Whole crop maize silage*

Mean ± SD (g DM sow−1 d−1) Median (g DM sow−1 d−1) Minimum (g DM sow−1 d−1) Maximum (g DM sow−1 d−1)

853.7 ± 219.3 897.5 402.0 1337.0

Whole crop wheat silage*

a

164.5 ± 117.4 126.5 10.0 590.0

b

Sugar beet pulp* 36.5 ± 46.9 16.0 1.0 251.0

c

* Offered over 3 h per day (d) ad libitum at randomly changing feeding places. Overall 20 d. a,b,c Mean values with different letters are significantly different at p ≤ 0.05.

3.2. Slurry quantification To compare the excrement quantities and thereby the impact on the farm-related environment between the two feeding variants, the entire material INPUT (Table 4) and OUTPUT (Table 5) were measured. The quantities shown in Tables 4 and 5 refer to 20 sows and 40 d per experiment. The major differences in material INPUT between the trials were the lack of MS and the reduced water intake by the animals in CON trial (Table 4), despite the increased indoor temperature (Table 2). MS trial included an overall of 1,440 kg fresh matter (FM) of MS (738 g DM sow−1 d−1) and 1,291 kg additional drinking water for the animals. Thus, the water intake was reckoned 15.28 l sow−1 d−1 in the MS trial and 13.67 l sow−1 d−1 in the CON trial. The slurry data also differ between the two trials (Table 5). In MS trial, the amount of slurry per sow was 3.99 m3 extrapolated to 1 year (yr), with 7.91 % DM content. In CON trial, it was only 2.54 m3 sow−1 yr−1 (DM 3.90 %). Therefore, there was 1.6 times more slurry in MS trial. The main differences were the amounts of floating layer and liquid manure (Table 6). The volume of the liquid phase was comparable between both trials (e.g., slurry channel 2), but the floating layer in MS trial was more than twice as thick as that in CON trial, after 40 d of feeding. The DM content of the floating layer and faeces (sample was taken directly after excretion) was higher in CON trial than in MS trial(17.58 % versus 28.66 %, respectively). The DM content of the liquid phase was more than twice as high in MS trial (5.43 %) than in CON trial (2.29 %).

3.3. Surface area pollution To evaluate the faecal pollution of the slatted floor in the different feeding trials, the floor area was divided into score-squares and rated once a day. As shown in Fig. 4(A), ad libitum feeding of MS (MS trial) led to significantly more polluted pen areas than restricted feeding (CON trial). In CON trial, there were more dry and clean pen areas and nearly no ‘wet and polluted’ pen areas. In MS trial, 8 % of the floor area was ‘wet and polluted’. The polluted surface area was comparable to the extent of slatted floor occlusion (Fig. 4 (B)). In both trials, the slots of the slatted floor were mostly free of excrements. Nevertheless, a marked proportion of occluded slots remained in the MS trial than in the CON trial without MS. Fig. 5 shows that in addition to the overall results of pollution in Fig. 4, the distribution of surface area pollution, as well as the percentage of occluded slots in the slatted floor, are within the pens, on a randomly selected day (17.05.2016) in MS trial. The slats were largely dry and clean, near the trough. Pollution of the surface area in the back-pen area became increasingly intense and was concentrated in the area around the nipple drinkers. Occluded slots were increasingly found in the back third of the pens. Fig. 6 shows the distribution of surface area pollution, as well as the percentage of occluded slots in the slatted floor, within the pens, on a randomly selected day (29.05.2016) in CON trial. The degree of pollution and occluded slots was lower overall, and the clean area in front of the trough was larger in the CON trial than in MS trial (Fig. 5). More polluted areas could also be found in the rear of the pen, in the area around the nipple drinkers. Occluded slots also appeared in this pen area but less than in MS trial (Fig. 5).

Table 4 Components of feeding stuff (INPUT, 20 sows, 40 days of feeding). Material INPUT

Amount INPUT MS trial (kg FM a)

DM

Maize silage Concentrated feed Water intake Sum

1,440 2,057 c 12,226 15,723

41.0 88.6 0.0

a b c

b

MS trial(%)

Fresh matter. Dry matter. Calculated, total amount of concentrated feed in trial. 6

Amount INPUT CON trial (kg FM a)

DM

b

– 2,057 c 10,935 12,992

– 88.6 0.0

CON trial (%)

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Table 5 Total slurry data (OUTPUT, 20 sows, 40 days [d] of feeding). Material OUTPUT

Amount OUTPUT MS trial (kg)

DM MS trial (%)

Slurry per sow−1 yr−1 MS trial (m3)

Amount OUTPUT CON trial (kg)

DM CON trial (%)

Slurry per sow−1 yr−1 CON trial (m3)

Slurry (total, 40 d)

8,750.00a

7.91b

3.99

5,560.00a

3.90b

2.54

a b

Calculated as the amount of both slurry channels minus the technical residue. Off-setting the dry matter (DM) of total mixed slurry minus the proportional DM of the technical residue.

Table 6 Amounts and dry matter (DM) of different slurry phases after 40 d of feeding in each trial (both filling levels, e.g., from slurry channel 2). Slurry phases

Filling level MS trial (m)

DM MS trial (%)

Filling level CON trial (m)

DM CON trial (%)

Floating layer Liquid phase Faeces

0.14 0.28 –

16.23 5.43 25.29

0.06 0.27 –

17.58 2.29 28.66

Fig. 4. A) Pollution of surface area depending on feeding strategy, rating results of score-squares. B) Occlusion of the slatted floor caused by the consistency and amount of slurry in two different feeding trials. Rating results of score-squares (y-axis transformed as disproportional power function).

4. Discussion 4.1. Preference of different silage types among pregnant sows The preference experiment was carried out in this study as a preliminary test, to identify which silage type was most preferred by the animals. It could be assumed that the silage that was eaten most by the animals would, subsequently, also produce the highest amount of slurry. For this reason, this was not a preference experiment in animal nutrition but was intended purely to determine the highest amount of slurry. Thus, the ‘worst case’ should be presented in relation to the amount of slurry and its impact on the farmrelated environment. MS was preferred by the pregnant sows in the preliminary test. Compared to the DM intake of whole plant MS, the sows ate only about one-fifth of whole plant wheat silage and only one-twenty-third of the sugar beet pulp. In a study by Hohmeier and Kamphues (2015) older fattening pigs were offered MS ad libitum in two periods. Unlike in this study, the author did not provide the animals with concentrated feed. The older fattening pigs consumed 1568 ± 45.5 g DM of MS per day in the first period (mean: 138 kg BW), and 1369 ± 140 g DM d−1 in the second period (mean: 177 kg BW). It could be seen that the intake of MS decreased slightly with increasing BW and age, but the spread between the individual animals (standard deviation) increased. The study was comparable to the present preference test, except that these were adult sows and that the usual farm amount of basic feed plus the two other crude fibre sources were given for choice. Therefore, the feed intake of MS in the current trial was relatively less, with 854.7 ± 219.3 g DM sow−1 d−1 (mean: 230 ± 28 kg BW), but the standard deviation was even higher. Differences between the pens and thereby individual differences among the animals were more apparent in older animals. MS was also consumed slightly more by pregnant sows in similar trials (Sievers and Kamphues, 2017), in comparison to whole plant wheat silage. In the present study, the differences between the DM intake were better distinguishable, corroborating the findings by Sievers and Kamphues (2017), where the whole plant wheat silage was eaten almost as much as MS. 7

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Fig. 5. Example of surface area pollution (denoted by colours) and slatted floor occlusion (denoted by strokes) on a randomly selected day (17.05.2016) in the MStrial.

Fig. 6. Example of surface area pollution (denoted by colours) and slatted floor occlusion (denoted by strokes) on a randomly selected day (29.05.2016) in the CON trial.

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Canh et al. (1998) found that sugar beet pulp-based feed rations fed to growing–finishing pigs resulted in a slurry with a 0.8 unit lower pH and over 50 % less ammonia emissions than that of the other three diets evaluated. In this context, and due to these positive influences on the environment, an increased intake of sugar beet pulp would be advantageous, but this was not seen in the current results. The farm on which the study was carried out breeds its own gilts. For this reason, it can be ensured that the three used fibrecontaining feedstuffs were completely unknown for the animals and they were able to prefer maize silage independently of previous experiences. 4.2. Slurry quantification When considering the resulting amount of slurry (OUTPUT), the amount (INPUT) of the used feed must also be recorded and considered. The amount of concentrated feed was intentionally the same in both feed variants. The water intake in the trials was around 10–15 l sow−1 d−1, which is consistent with previous data (Büscher et al., 2008; Mroz et al., 1995). Nonetheless, in the current study, there was a notable difference between the trials: in the MS trial, the sows absorbed more water despite the increased feed and crude fibre intake (Table 4). This difference occurred, despite the lower indoor temperature in the MS trial than in the CON trial (Table 2). In tests on the water intake of growing pigs, Yang et al. (1981) noted that the water intake increased when the feed was restricted. The authors explain it is an animal behaviour to protect against hunger. Robert et al. (1993) revealed that the time spent drinking and the daily water intake per sow were reduced if high crude fibre contents were fed in comparison to concentrated feed. Massé et al. (2003) also confirmed a decreased water intake in combination with fibrous feed rations, even without ad libitum supply of feed. These literature results were in contrast to our study. Further studies confirm with our results that more water is absorbed by the animals in diets containing fibrous feed. Philippe et al. (2015) identified this connection for fattening pigs with high fibre feeding. Due to the many contradictions in the literature on the water intake of pigs, no general justification can be found for these results. The water intake is often individually different. This could be due to the fact that the animals did not completely absorb the measured amount of water, but partly spilled it (Philippe et al., 2008). In addition to the differences in the amounts of drinking water, differences between the current trials naturally resulted from the use of MS in the MS trial. In comparison to the preliminary test, where the offered silages were available to the sows during a limited time (3 h), with competition observed at the feeding places, the MS in the MS trial was available ad libitum (24 h), in specially converted feeders, separated from the trough (Figs. 1 and 2). As a result, the sows consumed slightly less MS in the MS trial (738 g DM sow−1 d-1) than in the preliminary test. The data of the MS feed intake have already been discussed in Section 4.1. Furthermore, this result was in the range mentioned in the above literature, in connection with the addition of concentrated feed (cf. Sievers and Kamphues, 2017). Significantly more excrements were produced when feeding MS ad libitum in MS trial, amounting to 1.6-fold more, or 3.99 m³ slurry per sow extrapolated to 1 year versus only 2.54 m³ per sow and year in the CON trial. Massé et al. (2003) and Philippe et al. (2015) have also investigated the amount of slurry after feeding diets rich in crude fibre and after control diets with concentrated feed in pregnant sows. Extrapolated to one year, Massé et al. (2003) recorded after a very high fibre diet 3.71 m3 per sow and year. Philippe et al. (2015) determined 1.16 m3 per sow and year for a high fibre diet. The result of the trials in this study are higher because in our experiment the diet was offered ad libitum in comparison to the other two studies. During the control feeding, Massé et al. (2003) determined 4.52 m3 per sow and year, Philippe et al. (2015) found 1.59 m3 per sow and year. These values scatter strongly, our measured value lies in between with 2.54 m3. The feeding regime in control feeding was comparable in all three studies (restricted). The KTBL (2012) recorded a slurry amount of 4 m3 sow−1 yr−1 for a sow with 22 piglets raised up to 8 kg and on a standard feed, for the entire production cycle, including lactation. In the current study, only the sector of pregnant sows was considered, which could be compared best with the sector of gilts integration (without lactation) that stated 2.5 m³ sow-1 yr−1 (KTBL, 2012), which was very close to the slurry amount of the CON trial in the current study. Canh (1998) (growing–finishing pigs) and Philippe et al. (2015) (pregnant sows and fattening pigs) each conducted experiments in which sugar beet pulp-based diets and grain-based diets were offered restrictively not ad libitum. There were no differences in the amount of slurry between the groups with high-fibre diets and the grain-based control diets. In the present study, the diet rich in crude fibre was offered ad libitum, to improve animal welfare by extending the daily time of feed intake and decreasing hunger (Bergeron et al., 2000; Brouns et al., 1994) in pregnant sows. It was evident that the increase in total slurry amount in this experiment was purely due to the ad libitum available feed supply and not to the type of diet. Wiedmann (2011) verified that ad libitum feeding intensified excrement quantities. The advantages of prolonging the durations of feed intake and relaxation (calm, satisfied animals) could also be observed in the current study. Nevertheless, the increased feed consumption has an enormous impact on the farmrelated environment in cases of harvesting the feedstuffs and later storing and transporting the higher amount of slurry. The benefits for animal welfare must be evaluated against these financial disadvantages in further studies. Several prior works (Machmüller, 1994; Massé et al., 2003), described differences between urine and faecal masses after feeding diets with different fibre contents. In comparison to the grain-based diet there was more faeces and less urine from the animals that consumed the diet rich in crude fibre. The slurry viscosity was another factor, which, as described in the next section, influenced the flowability of the slurry. This separation in urine and faeces masses could not be shown in the current study, because the overall amount of slurry was recorded under practical conditions, similar to Philippe et al. (2015). The slurry DM contents differed between the two feed variants. The DM content of sows slurry in the CON trial (3.90 %) was similar to that presented by the KTBL (2012), in which the DM content of sows slurry was 4.00 %. In the present study, the DM content of sows’ slurry in the MS trial was 7.91 %. This value is about twice as high as in the CON trial and approaches the content of 9

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dairy cows slurry, of 11 % DM (KTBL, 2012). Massé et al. (2003) assessed the effects of three isoenergetic diets of very-high-fibre (VHF) and high-fibre (HF) content and a concentrated diet (C) as the control, on the produced slurry. In contrast to the current study (MS trial), the diets were not fed ad libitum. Diet C (below 10 % DM) led to a liquid slurry with 3.79 % DM, whereas the HF (11.11 % DM) and VHF (18.29 DM) diets produced semi-solid slurry displaying between 10 and 20 % DM (Massé et al., 2003). This trend was confirmed in the current study. In absolute terms, the DM contents were not as high as those presented by Massé et al. (2003). One reason for this discrepancy is that in our study the adjunctive drinking water was also recorded by the measuring method. This approach is advantageous since Massé et al. (2003) proposed the addition of water to change the semi-solid slurry to flowable material. The higher the fibre content in the diet, the higher the apparent viscosity increased significantly (without the addition of water). Furthermore, the increased DM content of the slurry rich in fibre in the MS trial of the present study reduced its flowability compared to the CON trial without fibre addition. The DM contents described in the previous paragraph refer to the total homogenised slurry. Compared to the conditions prevailing in common pig housing systems, this is an idealised representation. Only very few pig farms have permanently installed slurry stirrers. Regular stirring of the slurry is unavoidable (Kleine, 2012). Otherwise, the solid and liquid components separate in the slurry channel and form floating layers under practical conditions. The present experiment showed marked differences in the thickness of the floating layers after feeding the different diets. While the liquid phases under the slatted floors between the variants had approximately the same height, the floating layer in the MS trial (0.14 m) was more than twice as thick as the floating layer of the CON trial (0.06 m) after 40 d, and caused problems when discharging the slurry. The liquid phase flowed first into the discharging pipes while the solid components remained in the slurry channel. The thicker the floating layers, the less they mixed with the liquid phase. The solid material gradually built up, and the slurry channel and pipes became gradually blocked. Kolle (2008) described similar problems, with very thick floating layers of 0.3–0.4 m when feeding MS to pregnant sows on slatted floors. Only slurry channels with a depth of at least 1.80 m should be installed in the barns, to avoid such issues occurring. Another concern linked to thick floating layers is the large number of flies in the barn, which is a nuisance for the animals and reduces animal welfare. For this reason, it is important to destroy the floating layers regularly, because they are often the breeding sites of the flies (Kleine, 2012; Kolle, 2008). 4.3. Surface area pollution As could be seen in Section 3.3, there were differences in floor cleanliness after feeding the two different diets. Overall, the largest proportion of the pen areas in both variants was ‘dry and clean’. Nevertheless, more ‘polluted’ or ‘wet and polluted’ surface areas could be found in the MS trial than in the CON trial, and could mainly be explained by the higher amount of excrements (Table 5), which was caused by the nature of the used diet. The increased amount of excrements after feeding diets containing high contents of crude fibre has already been described (Massé et al., 2003; Sievers and Kamphues, 2017). The higher amount of excrements was deposited by the animals on the existing barn area and then resulted in greater pollution of the existing surface area. It implies that feeding strategy has a side-effect on the cleanliness of the barn floor area (Plonait, 2004). Table 6 shows that the excrements in the MS trial had a lower DM content than those in the CON trial. Similarly, decreased DM contents in excrements with higher crude fibre contents in the used diets have been verified in literature (Hansen et al., 2007; Kleine, 2012; Preißinger et al., 2016; Tabeling et al., 2003). Hohmeier and Kamphues (2015) have also established this connection in their investigations and explain it with the higher water binding capacity of the fibres in ingesta. This could also be the reason why animals fed rations rich in crude fibres absorb more water than a comparable control group (see above in this chapter). In connection with the higher slurry mass in the MS trial versus CON trial, it can be assumed that softer and structured excrements were harder for the sows to penetrate into the slatted floor and smear the slots, which was also seen at Preißinger et al. (2016). The occlusion of slatted floors when using silages are due to the coarse forage structure of the silage (Hohmeier et al., 2016; Kamphues et al., 2016). According to Wiedmann (2011), pens with ad libitum feeding had the worst floor cleanliness and added that dried beet pulp containing crude fibre led to a smeary faeces consistency. In the MS trial, the softer faeces, relative to the CON trial, containing crude fibre also blocked individual slots, as evidenced in Figs. 5 and 6, which led to poor floor cleanliness. Sows prefer to deposit their excrements in wet areas (Wiedmann, 2011). Indeed, in the present study, the wet spots around the nipple drinkers were preferably used for defecating. This poor floor cleanliness in these wet and polluted areas poses an increased risk for claw diseases, because of increased slipping of the animals, for example, during ranking fights. In addition, a polluted environment causes softening of the claw horn, facilitating bacterial penetration (Wiedmann et al., 2011). The risk of helminthiasis and Salmonella transmission increases with dirty floor surfaces and direct contact with excrements (Von Borell and Huesmann, 2009). Australian studies have shown that dry lying and activity areas should be offered to sows, not only to reduce the risk of infection but for animal welfare as well. In the experiment, for example, the sows had a distinct preference for the dry pen areas. If feed was presented only in the wet area, the sows changed to the dry area immediately after feed intake (Hutson et al., 1993). For these reasons, polluted floor areas have negative impacts on animal welfare. Among other factors, a high degree of contamination of the slatted floor promotes the release of ammonia (Sieber et al., 2003). Janssen and Krause (1987) assumed that only 9 % of the total release of odorous substances originates directly from the animals while 91 % comes from contaminated surfaces, especially from the barn floor, so the aim is to minimize the soiled surfaces. If sows should be fed ad libitum with high crude fibre contents to achieve better satiety, it may be advantageous to install individual pen areas with slatted floors containing a high degree of perforation, as described previously (Gallmann et al., 2000), for example, with plastic slats. Another alternative would be the use of permanently installed slurry scrapers or scraper robots to remove regularly excrements from the contaminated floor areas during ad libitum feeding. In large pens and group sizes, a technique such as the one examined by Ebertz et al. (2019) can be used as an alternative. However, such polluted areas of slatted floors need special 10

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maintenance (cf. Preißinger et al., 2016). 5. Conclusions The present study quantified the slurry produced under field conditions after ad libitum feeding of diets rich in crude fibre. Up to now, an improvement in the animal welfare situation has rarely been compared with influences on resulting slurry parameters and technical requirements. The current results show that ad libitum feeding of MS caused a 1.6-fold more slurry when compared to restricted feeding. In addition, the barn floors and, consequently, the animals were visibly more polluted with excrements. Further field studies should be conducted to consolidate the results that have practical effects on the storage and the transport of the slurry. Funding This work was supported by the German Government’s Special Purpose Fund held at Landwirtschaftliche Rentenbank, grant number 745 625. The Federal Office of Agriculture and Food (BLE) provided the professional supervision (grant number 28RZ-372.063). Declaration of Competing Interest None. Acknowledgment The authors thank the animal housing owner for the opportunity to achieve this study on his farm. References Barnett, J.L., Hemsworth, P.H., Cronin, G.M., Jongman, E.C., Hutson, G.D., 2001. A review of the welfare issues for sows and piglets in relation to housing. Aust. J. Agric. Res. 52, 1–28. https://doi.org/10.1071/AR00057. Bergeron, R., Bolduc, J., Ramonet, Y., Meunier-Salaün, M.C., Robert, S., 2000. Feeding motivation and stereotypies in pregnant sows fed increasing levels of fibre and/ or food. Appl. Anim. Behav. Sci. 70, 27–40. https://doi.org/10.1016/S0168-1591(00)00142-8. Bohnenkemper, O., Steffens, G., 2006. Gülle - Mengen genau ermitteln, Proben richtig ziehen/ Liquid Manure - Determine Quantities Accurately, Draw Samples Correctly. KTBL, Darmstadt. Brouns, F., Edwards, S.A., English, P.R., 1994. Effect of dietary fibre and feeding system on activity and oral behaviour of group housed gilts. Appl. Anim. Behav. 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