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Dairy cows prefer shade that offers greater protection against solar radiation in summer: Shade use, behaviour, and body temperature
Applied Animal Behaviour Science 116 (2009) 28–34
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Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
Dairy cows prefer shade that offers greater protection against solar radiation in summer: Shade use, behaviour, and body temperature Karin E. Schu¨tz a,*, Andrea R. Rogers a, Neil R. Cox b, Cassandra B. Tucker c a
AgResearch Ltd., Agricultural Systems, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton, New Zealand AgResearch Ltd., Bioinformatics, Mathematics & Statistics, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton, New Zealand c University of California, Department of Animal Science, 1 Shields Avenue, Davis, CA 95616, United States b
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 4 July 2008 Available online 23 August 2008
There is considerable evidence that shade is a valuable resource for cattle in summer, but less is known about the important design features of effective shade. The aim of this experiment was to investigate if lactating dairy cows have a preference for shade that offers greater protection against solar radiation. Shade was provided by wooden structures covered with shade cloth that blocked 25, 50 or 99% of solar radiation. Nine groups of Holstein–Friesian cows (27 animals in total, 3 animals/group) were exposed to three treatment combinations: pair-wise simultaneous presentation of shade cloth that blocked: (1) 50 and 99%, (2) 25 and 50%, and (3) 25 and 99% of solar radiation. Cows were exposed to each combination in a cross-over design (2 d/combination). Shade use and time budgets were recorded during the hottest part of the day (10:00–17:00 h). Within each group, cows were categorised as predominantly black, white, or black and white in colour (one of each coat colour/group) in order to investigate the interaction between coat colour and treatment choice. Cows preferred shade cloth that blocked greater amounts of solar radiation in two of the combinations (99% versus 25%: 72.3% time spent in the 99% option, P < 0.001, S.E.: 3.9%; 50% versus 25%: 72.0% time spent in the 50% option, P < 0.001, S.E.: 3.5%), but showed no preference for shade cloth that blocked 50 or 99% of solar radiation when these two options were presented simultaneously (49.8% time spent in the 99% option, P = 0.509, S.E.: 5.3%). Neither coat colour nor weather conditions influenced preference for shade type. Cows spent more time in shade on days with higher solar radiation levels (P < 0.001, slope: 0.04%, S.E.: 0.01%) and higher ambient air temperature (P = 0.021, slope: 2.63%, S.E.: 0.02%). Mean body temperature increased with increasing temperature–humidity index (P = 0.014, slope: 1.9%, S.E.: 0.7%), heat load index (P = 0.009, slope: 0.6%, S.E.: 0.2%) and ambient air temperature (P = 0.065, slope: 2.1%, S.E.: 1.1%). In conclusion, cows preferred shade that provided more protection from solar radiation (50 and 99% blockage versus 25%) and showed behavioural and physiological changes associated with increased heat load. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Behaviour Body temperature Coat colour Dairy cattle Heat load Shade
1. Introduction Exposure to summer weather affects both the behaviour and physiology of cattle. Increased heat load, caused
* Corresponding author. Tel.: +64 7 838 5571; fax: +64 7 838 5038. E-mail address: [email protected] (K.E. Schu¨tz). 0168-1591/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2008.07.005
by environmental factors such as air temperature, relative humidity, wind speed and solar radiation, elicits behavioural and physiological responses, including increased body temperature and respiration rate, and reduced activity and feed intake (Hahn, 1999; Ominski et al., 2002; West, 2003; Tapkı and S¸ahin, 2006). Hot and humid weather may also negatively affect breeding performance in dairy cattle by reducing fertility (Roman-Ponce et al.,
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1977; De Rensis and Scaramuzzi, 2003). Excess heat load can in extreme cases severely compromise animal welfare and result in death (Armstrong, 1994). Cows readily use shade when given access to it and the provision of shade can alleviate negative effects of heat load (Kendall et al., 2006; Tucker et al., 2008). There is evidence that dairy cows value access to shade highly in hot weather by choosing to stand in shade over lying when deprived of lying for 12 h (Schu¨tz et al., 2008). However, little is known about which physical aspects of shade are important to cows. This knowledge is important in order to design and provide optimal shade for cattle. Various types of shade, such as trees or man-made structures, create different microclimates and studies have shown that cows prefer specific types of shade. For example, Gaughan et al. (1998) demonstrated that a single group of lactating Holstein–Friesian cows in Queensland, Australia, preferred shade created by an iron roof to shade cloth (70% blockage of solar radiation), choko vines or single trees, when given access to all types of shade simultaneously. The iron roof in the study by Gaughan et al. (1998) provided greater protection against solar radiation than the shade cloth or the choko vines, but the iron roof was also located such that it also had less solar radiation from the sides, due to shading from the other treatments. Thus, it is possible that the interaction between location and shade type influenced the preference for the iron roof. Others have reported that cows prefer shade created by trees rather than man-made structures due to the efficiency in blocking solar radiation and evaporation from leaves, which cools the surrounding air (e.g. Shearer et al., 1991). Trees, however, can have a short life-span in pastures with large dairy herds (Shearer et al., 1991) and, therefore, provision of other shade types may be more practical. Tucker et al. (2008) demonstrated that dairy cows with access to shade that provided more protection from solar radiation spent more time using this resource than cows with access to shade that provided less protection. All cows spent more time in the shade on days with higher levels of solar radiation and within a day, shade use peaked when solar radiation levels were highest. In addition to ambient conditions, some previous studies have demonstrated that coat colour can influence the response to heat; dark-coated animals are more sensitive to heat stress (e.g. Finch, 1984; Brown-Brandl et al., 2006a). In contrast, Tucker et al. (2008) found that darker coloured cows used shade less than lighter animals when shade blocked 99% of solar radiation, creating an unclear picture of how coat colour affects shade use and response to heat load. The aim of this study was to investigate dairy cattle preferences for shade offering greater protection from solar radiation. In addition, this study aimed to describe the effects of coat colour, body temperature and weather conditions on these preferences. It was predicted that cows would prefer shade that offered greater protection from solar radiation and that these preferences would be pronounced on hot days, particularly if body temperature was high or if cows had dark coats.
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2. Materials and methods 2.1. Animals and treatments All procedures involving animals were approved by the Ruakura Animal Ethics Committee under the New Zealand Animal Welfare Act 1999. The study utilised 27 Holstein–Friesian dairy cows in mid-lactation that ranged from 4 to 9 years of age and were 193 22 (mean S.D.) d in milk at the start of the experiment. They weighed 510 43 kg (mean S.D.) and had a body condition score between 4 and 5 on a 1–10 scale (Roche et al., 2004). All cows utilised in this study had been used previously in the study by Tucker et al. (2008). All cows were accustomed to the shade structures and to the presence of observers. Previous experience with each shade type was balanced in this experiment. The cows were milked twice daily (approximately at 06:30 and 14:00 h). Cows were categorised as predominantly black (96 3% black hair), white (25 8% black hair), or black and white (60 7% black hair). The percentage of black hair was estimated from digital photographs of both sides of each cow using image analysis software (Scion Image v.4.0.2, Scion Corporation, Frederick, USA). The animals were tested as 9 groups (3 cows/group, n = 9) at the AgResearch Number 1 and 2 Dairies near Hamilton, New Zealand (latitude 378470 S, longitude 1758190 E). The groups of cows were balanced for coat colour category (one of each: black, black and white, and white cow in each group). Shade cloth (Donaghys Industries Ltd., Christchurch, New Zealand) that blocked either 25, 50 or 99% of solar radiation was presented in a pairwise manner, resulting in three treatment combinations: (1) 50 and 99% solar radiation blocked, (2) 25 and 50% solar radiation blocked, and (3) 25 and 99% of solar radiation blocked (n = 9 groups/combination, Fig. 1). Pairwise presentation was used to assess the relative ranking of each type of shade. Groups were rotated through these three treatment combinations in a balanced cross-over design (2 d/combination). The shade cloth was mounted onto wooden structures. Each group was provided with 4 wooden shade structures, two of each level of protection from solar radiation (Fig. 1). To prevent any overlap in shade cast, there was a distance of 10 m between each structure. Each structure provided a shaded area of 12 m2 (total shade area: 48 m2, 16.0 m2 of shade/cow) and had a 1 m section of the legs painted at 1–2 m height (99, 50, 25%; green, red, yellow respectively) in order to facilitate observations and provide the animals with a visual cue for the 3 types of shade cloth. All structures had a mown patch of grass (3.5 m 4.5 m) beneath them in order to minimise grazing activities in the shaded area. Each structure also had a rectangle perimeter of 3 m 4 m identified clearly with white paint directly beneath the structure. Both the mowed patch of grass and painted rectangle facilitated behavioural observations. The cows always had access to a water trough located 7–10 m away from the structures. Three groups were tested simultaneously for 6 d, 2 d in each treatment combination, with one of each of the combinations tested at the same time for a total of 18 d of testing during February and March 2006 (southern hemisphere summer). Cows were moved into the treatment areas at approximately 08:00 h where they had access to the shade structures until approximately 17:30 h. A fresh sward of grass was provided at approximately 08:00 h each day. Following completion of observations, all cows were moved onto a pasture without the shade structures, adjacent to the treatment area, where they spent the night and were provided with another fresh sward of grass. This strategy minimised the number of times the shade structures were moved because fresh grass was also provided in a separate area. 2.2. Environmental measurements Weather measurements (ambient air temperature, relative humidity, wind speed, rainfall, solar radiation and black globe temperature) were recorded and the temperature–humidity index (THI) and heat load index (HLI) were calculated at 10 min intervals during the 18 d trial as reported by Tucker et al. (2008). All weather measurements were taken in a field adjacent to the observation area (2 m away). The microclimate (air temperature, black globe temperature and relative humidity) beneath the 3 types of shade cloth and in an adjacent control pasture (no shade) was recorded at 10 min intervals with HOBO Pro Dataloggers (Onset Computer Corporation, Bourne, MA, USA) between 10:00 and 17:00 h during the 18 d of data collection. 2.3. Behavioural measurements Time budgets and shade use were recorded using instantaneous scan sampling (Martin and Bateson, 1993) every 10 min during the hottest part
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Fig. 1. Diagram of the treatment areas. Groups of cows (one black, black and white, and white cow/group) were offered two types of shade per treatment combination (25 or 50%, 25 or 99%, 50 or 99%).
of the day (10:00–17:00 h) on all 18 d of testing. The observations were interrupted by milking between 14:00 and 15:00 h (milking lasted 68 10 min, mean S.D.). The groups were observed for 2 h after returning from milking, i.e. all groups were observed for 6 h each day. Each replicate (3 groups of cows tested at the same time, one of each treatment combination) was observed simultaneously by trained staff (multiple observers were used to collect the behavioural information). Time budget information was recorded for lying, standing, and grazing. Cows were considered lying if their flank was in contact with the ground and standing was defined as not lying. Cows were considered to be grazing if grass was being ingested or could be seen in the mouth. The use of the shade structures was measured in two ways as described in Tucker et al. (2008): if at least one hoof was within/on the painted rectangle directly underneath the shade structure and/or at least one hoof was within the shadow cast by the structure. The second measurement was only taken when the outline of the shadow cast by the structure was clearly defined. Both measures were used because recording only the latter would likely underestimate shade use when the shadow was not clearly defined. Cows were identified with coloured collars and paint on the rump (Tell tail paint, FIL NZ Ltd., Mount Maunganui, New Zealand). Inter-observer reliability, as measured by percentage agreement, was between 96 and 100% for all behaviours. Interobserver agreement was lowest when assessing time spent grazing. 2.4. Body temperature Internal body temperature was recorded every 10 min using a modified vaginal controlled internal drug release insert (CIDRTM; InterAg, Hamilton, New Zealand) fitted with a microprocessor-controlled MinilogTX data logger (Vemco Ltd., Shad Bay, Nova Scotia, Canada). Temperature loggers were inserted into the vaginal cavity for the 6 d of testing. One temperature logger of a white cow malfunctioned and therefore data from 26 of the 27 cows were used in the analysis of body temperature. 2.5. Statistical analysis All data were averaged daily across the observation period for each treatment combination (10:00–17:00 h, 18 d in total). The results regarding shade use were the same regardless of whether shade use was estimated with the measure ‘‘standing in shadow cast by the structure’’ or ‘‘standing directly under the structure.’’ Therefore, a combination of the two measures was used (total shade use) and is presented throughout the rest of this paper. The proportions of total shade use, preference for shade type (proportion of time spent using the shade cloth that blocked more solar radiation), behaviours (grazing, lying, standing, and standing without grazing), and mean daily body temperature were analysed in a Generalised Linear Mixed Model (GLMM) in GenStat with random effects of group, day, animal, day by animal interaction and interactions between group and treatment combination. The fixed effects included coat colour, treatment
combination, and coat colour by treatment combination interaction. The GLMM allows modelling of the correlation structure arising from correlated behaviour of animals within a group, repeat measurements on the same animals, on the same days etc., while maintaining the appropriate distributional assumptions (in this case, binomial). To estimate the slope of the relationship between response variables and THI, HLI, ambient air temperature and solar radiation, response variables were averaged across the 3 cows for each group and day. In addition, the slope was calculated for the relationship (across animals) between body temperature measures [mean, minimum, maximum, amplitude (maximum minimum) during the 6 h observation period] and both shade use and preference for shade type on each day (9 points/d were used to generate slopes).
3. Results 3.1. Environmental conditions Air temperature, black globe temperature, wind speed, humidity, rain fall and solar radiation recordings during the trial and calculated THI and HLI values are summarised in Table 1. Ambient temperature, solar radiation, HLI and THI are all measures of heat load. We present relationships with all four of these weather variables to facilitate comparisons with other papers. 3.2. Shade use and behaviour In this study, shade was clearly defined on all four sides of the shadow cast by the structure in 45 33% (mean S.D.) of the scan samples per day, range 0–100%/d. When shade cloth that blocked 25 and 99% of solar radiation were provided simultaneously, the cows preferred the shade cloth that blocked more solar radiation (72.3% time spent in 99% option, P < 0.001, S.E.: 3.9%, Fig. 2). When shade cloth that blocked 25 and 50% of solar radiation were provided simultaneously, the cows again preferred the shade cloth that blocked more solar radiation (72.0% time spent in the 50% option, P < 0.001, S.E.: 3.5%, Fig. 2). The cows did not show any preference for shade cloth that blocked 50 or 99% of solar radiation when these were presented simultaneously (49.8% time spent in the
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Table 1 Summary of meteorological records for the 18 d of testing in summer during the observation period (10:00–17:00 h) and over 24 h Weather variable
Temperature (8C) Black globe temperature (8C) Relative humidity (%) Solar radiation (W/m2) Wind speed (km/h) Rainfall (mm/d) THIa HLIb
No shade (24 h)
No shade day-time (10:00–17:00 h)
25% blockage (10:00–17:00 h)
50% blockage (10:00–17:00 h)
99% blockage (10:00–17:00 h)
Mean
Range
Mean
Range
Mean
Range
Mean
Range
Mean
Range
16 17 72 218 6 2 59 53
1–24 0–33 32–94 0–1171 0–27 0–9 35–72 35–100
20 24 58 582 11 0 65 62
13–24 15–33 32–92 36–1171 0–27 0–2 56–72 42–98
20 23 63 n/a n/a n/a 66 n/a
14–24 15–34 31–100 n/a n/a n/a 56–75 n/a
20 22 64 n/a n/a n/a 66 n/a
14–25 14–31 32–100 n/a n/a n/a 57–72 n/a
20 21 64 n/a n/a n/a 66 n/a
14–24 14–26 35–100 n/a n/a n/a 57–72 n/a
The measurements were taken in a nearby pasture without any shade and underneath each shade cloth blocking different amount of ambient solar radiation (25, 50 and 99%). Both mean values and ranges (minimum to maximum) are presented. a Temperature–humidity index. b Heat load index.
Fig. 2. Average preference for shade type that blocked more solar radiation (indicated in bold on x-axis label). Bars are the group mean and each symbol represents one cow of each coat colour: predominantly black, white, or black and white (b/w).
99% option, P = 0.509, S.E.: 5.3%, Fig. 2). No interaction between preference for shade type and coat colour was found (P 0.419). None of the measured weather variables (solar radiation, ambient air temperature, THI or HLI) had any influence on preference for shade type (P 0.272).
The cows, on average, used shade during 29.8% (range: 0–64.9%) of the observation period per day, which corresponds to 1.8 h with a range of 0–3.9 h/6 h observation. Cows spent more time in shade on days with higher solar radiation levels (P < 0.001, slope:
Fig. 3. Total shade use (h/6 h of observations) by dairy cows between 10:00 and 17:00 h on days with different levels of solar radiation. Each point is an average of nine cows (S.E.M.) per day.
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Fig. 4. Total shade use (h/6 h of observations) by dairy cows between 10:00 and 17:00 h on days with different ambient air temperature. Each point is an average of nine cows (S.E.M.) per day.
Table 2 The behaviour and total shade use (mean S.E.D.) of cows with different coat colour (predominantly black, white, or black and white, one coat colour/group, n = 9 groups) between 10:00 and 17:00 h (interrupted by 1 h of milking between 14:00 and 15:00 h) on pasture in summer Behaviour (h/6 h of observation)
Lying Grazing Standing, not grazing Shade use
Coat colour Black and white
Black
White
0.1a 2.7 3.0 1.3
0.1a 2.8 3.0 1.8
0.2b 2.7 2.9 1.7
S.E.D.
P-value
0.09 0.23 0.26 0.38
0.050 0.870 0.805 0.312
Superscripts of different letters indicate a significant difference.
0.04%, S.E.: 0.01%, Fig. 3) and higher ambient air temperature (P = 0.021, slope: 2.63%, S.E.: 0.02%, Fig. 4). This pattern was also apparent with THI (P = 0.085, slope: 1.36%, S.E.: 0.8%), but not with HLI (P = 0.144, slope: 0.36%, S.E.: 0.3%).
Time budgets of cows with different coat colours are summarised in Table 2. Time spent on lying, grazing or standing without grazing during the observation period was not affected by solar radiation, air temperature, THI or HLI (P 0.271).
Fig. 5. Relationship between body temperature (mean, minimum and maximum values) and temperature–humidity index (THI), heat load index (HLI), air temperature and solar radiation of dairy cows observed between 10:00 and 17:00 h. Each point is the mean body temperature of nine cows per day.
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3.3. Body temperature during the observation period (10:00–17:00 h) Body temperature changed in response to weather conditions (Fig. 5). Cows had higher mean body temperature with increasing THI (P = 0.014, slope: 1.9%, S.E.: 0.7%), HLI (P = 0.009, slope: 0.6%, S.E.: 0.2%) and ambient air temperature (P = 0.065, slope: 2.1%, S.E.: 1.1%). Cows also had higher maximum body temperature with increasing air temperature (P = 0.020, slope: 4.1%, S.E.: 1.7%), THI (P = 0.004, slope: 3.5%, S.E.: 1.2%) and HLI (P = 0.004, slope: 1.1%, S.E.: 0.4%) and with decreasing solar radiation (P = 0.023, slope: 0.04%, S.E.: 0.02%). Furthermore, cows had higher amplitudes in body temperature (maximum – minimum) with increasing THI (P = 0.038, slope: 3.3%, S.E.: 2.3%) and HLI (P = 0.067, slope: 0.9%, S.E.: 0.5%) and with decreasing solar radiation (P = 0.012, slope: 0.06%, S.E.: 0.02%). There was no statistically significant relationship between minimum body temperature and any weather variables (P 0.261). 4. Discussion Dairy cattle preferred shade that offered protection against 50 and 99% of solar radiation over shade cloth that blocked only 25% of solar radiation. There were small differences in THI beneath the types of shade, whereas the black globe temperature, which incorporates the effects of solar radiation, decreased by 1 8C per 25% blockage. This suggests that the cows preferred the more protective shade cloth based on differences in solar radiation or ambient temperature, rather than other factors. These findings are in accordance with the results of Tucker et al. (2008) who demonstrated that cows spend more time under shade cloth that blocked more solar radiation. There were no preferences for shade cloth that blocked either 50 or 99% solar radiation when offered simultaneously. There are at least two possible reasons for this. Firstly, the dairy cows may not be able to distinguish between the shade cloth blocking 50 and 99% of solar radiation. This explanation however, is not supported by the findings in other studies. Tucker et al. (2008) found that cows spent more time in shade that offered greater protection against solar radiation, although the difference in shade use between 50 and 99% was smaller (0.3 h/15.5 h or 9% difference in shade use) than the difference between 99 and 25% (2.0 h/15.5 h or 60% difference in shade use). Furthermore, Bennett et al. (1984/1985) demonstrated that shorthorn steers preferred shade cloth that blocked 80% of solar radiation over 50 and 70%, whereas there was no significant difference in shade use between the 50 and 70%. Thus, cattle can distinguish between shade differing by 10% in protection from solar radiation, a value smaller than the 49% difference between the options presented in the current experiment. Secondly, the microclimate beneath the shade blocking 50 and 99% of solar radiation may have provided equal cooling opportunities in the weather conditions during the trial (air temperature was never above 25 8C). It was on average 1, 2 and 3 8C cooler underneath the 25, 50 and 99% options respectively compared to the area without shade.
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These differences are difficult to interpret as there is no information on whether 22 8C (50% blockage) and 21 8C (99% blockage) provide similar cooling opportunities in 24 8C ambient conditions from the animal’s point of view. The literature in this area can be broadly categorised in two ways. The first type of study defines thresholds for when weather conditions are problematic for cattle either before the study (Brown-Brandl et al., 2005) or from their dataset (Muller et al., 1994; Fisher et al., 2002). Other studies describe the nature of the relationship between shade use (or other measures of heat load) and ambient conditions (Tucker et al., 2008). The results from these studies are variable and often highly dependent on local conditions. Further research is needed to understand how preference for different shade types is affected by weather variables, particularly during more extreme weather conditions. Indeed, previous research in the same area found that dairy cows increased their use of shade when ambient temperatures exceeded 25 8C (Fisher et al., 2002). Although average ambient air temperature was 20 8C during observations in the current trial (range: 13–24 8C) the cows readily used shade. Use of shade when ambient conditions are below 25 8C may play a role in thermoregulation, that is, these behavioural changes may help prevent the dramatic increase in panting that has been reported for beef cattle when temperatures rise above 25 8C (Brown-Brandl et al., 2006b). However, there may also be other reasons for cattle to use shade, such as avoidance of the harmful effects of solar radiation on skin and eyes. Little is known about the motivation for shade seeking behaviour and mechanisms underlying shade use could be an interesting area for future work. Cows spent more time in shade on days with higher levels of solar radiation and air temperature. Similar results have been found by others; for example Tucker et al. (2008) also found a positive relationship between shade use and ambient solar radiation. Furthermore, Bennett et al. (1984/1985) reported that steers of several beef breeds spent more time in shade as ambient temperatures and solar radiation levels increased. In the current study, cows spent more time in shade with increasing air temperature even though air temperature and THI never reached levels previously reported to have negative effects on the physiology and production of dairy cattle (air temperature of 25 8C, THI of 72, e.g. Muller et al., 1994; West et al., 2003). There is evidence that cooling dairy cows with shade or sprinklers lowers their body temperature when THI equals 67 (Kendall et al., 2007), which suggests that dairy cows benefit from cooling opportunities under a wider range of ambient conditions than previously reported. Cattle seek shade in response to increased heat load. Other behavioural responses to increased heat load include a reduction in time spent lying and grazing (Overton et al., 2002; Za¨hner et al., 2004; Tucker et al., 2008). It has been suggested that cattle stand as a way to maximise the surface area exposed to the environment and increasing the airflow around the body (e.g. Ansell, 1981). In this study, behavioural changes were in general not found. However, light coloured cows spent more time lying than dark-coloured cows, which suggests that the cows with
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predominantly white coats were less affected by warm weather. Dark-coloured cattle are thought to be more sensitive to heat stress than light coloured cattle (e.g. Hansen, 1990; Gaughan et al., 1998; Brown-Brandl et al., 2006a). However, neither shade use nor body temperature measurements in this study provided any support for this idea. It is possible that dark-coloured cows change their behaviour earlier than lighter coloured cows in response to increased heat load in order to thermoregulate, for example by reduced lying times. Thus, differences in thermoregulatory behaviour could explain the similarity in body temperature between predominantly black and white cows. Mean body temperature between 10:00 and 17:00 h increased with increasing THI and HLI. In addition, maximum body temperature increased and the amplitude in body temperature (maximum–minimum) was greater with increasing air temperature, THI, and HLI. Similar findings have been reported by others including Muller et al. (1994) and Kendall et al. (2007). 5. Conclusions Dairy cows exhibited both behavioural and physiological changes in response to warm weather, including increased body temperature and shade use. Cows showed clear preferences for shade that offered greater protection from solar radiation. The cows readily used the shade even on cool days, which suggests that shade is an important resource during summer. Acknowledgements The authors gratefully acknowledge the technical assistance from AgResearch staff: Kate Brown, Katie Carnie, Antonia Davies, Debbie Davison, Suzanne Dowling, Cara Hansen, Frankie Huddart, Paul Kendall and Haley Shepherd. We also thank the staff at AgResearch No. 1 and 2 Dairies, Ron Clarke, Bob Smith and Kevin Orr. This work was funded by the Foundation for Research, Science and Technology. References Ansell, R.H., 1981. Extreme heat stress in dairy cattle and its alleviation: a case report. In: In: Clark, J.A. (Ed.), Environmental Aspects of Housing for Animal Protection. Butterworths, London, United Kingdom, pp. 285–306. Armstrong, D.V., 1994. Heat stress interaction with shade and cooling. J. Dairy Sci. 77, 2044–2050. Bennett, I.L., Finch, V.A., Holmes, C.R., 1984/1985. Time spent in shade and its relationship with physiological factors of thermoregulation in three breeds of cattle. Appl. Anim. Behav. Sci. 13, 227–236. Brown-Brandl, T.M., Eigenberg, R.A., Nienaber, J.A., Hahn, G.L., 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle. Part 1. Analyses of indicators. Biosyst. Eng. 90, 451–462.
Brown-Brandl, T.M., Nienaber, J.A., Eigenberg, R.A., Mader, T.L., Morrow, J.L., Dailey, J.W., 2006a. Comparison of heat tolerance of feedlot heifers of different breeds. Livest. Sci. 105, 19–26. Brown-Brandl, T.M., Eigenberg, R.A., Nienaber, J.A., 2006b. Heat stress risk factors of feedlot heifers. Livest. Sci. 105, 57–68. De Rensis, F., Scaramuzzi, R.J., 2003. Heat stress and seasonal effects on reproduction in the dairy cow—a review. Theriogenology 60, 1139– 1151. Finch, V.A., 1984. Heat as a stress factor in herbivores under tropical conditions. In: Gilchrist, F.M.C., Mackie, R.I. (Eds.), Herbivore Nutrition in the Subtropics and Tropics. The Science Press, Graighall, South Africa, pp. 89–105. Fisher, A.D., Roberts, N., Matthews, L.R., 2002. Shade: its use by livestock and effectiveness at alleviating heat challenge. Report to MAF Policy. New Zealand. Gaughan, J.B., Goodwin, P.J., Schoorl, T.A., Young, B.A., Imbeah, M., Mader, T.L., Hall, A., 1998. Shade preferences of lactating Holstein-Friesian cows. Aust. J. Exp. Agric. 38, 17–21. Hahn, G.L., 1999. Dynamic responses of cattle to thermal heat loads. J. Anim. Sci. 77, 10–20. Hansen, P.J., 1990. Effects of coat colour on physiological responses to solar radiation in Holsteins. Vet. Rec. 127, 333–334. Kendall, P.E., Nielsen, P.P., Webster, J.R., Verkerk, G.A., Littlejohn, R.P., Matthews, L.R., 2006. The effects of providing shade to lactating dairy cows in a temperate climate. Livest. Sci. 103, 148–157. Kendall, P.E., Verkerk, G.A., Webster, J.R., Tucker, C.B., 2007. Sprinklers and shade cool cows and reduce insect-avoidance behavior in pasturebased dairy systems. J. Dairy Sci. 90, 3671–3680. Martin, P., Bateson, P., 1993. Measuring Behaviour. An Introductory Guide, 2nd edn. Cambridge University Press, Cambridge, UK. Muller, C.J.C., Botha, J.A., Coetzer, W.A., Smith, W.A., 1994. Effect of shade on various parameters of Friesian cows in a Mediterranean climate in South Africa. 2. Physiological responses. S. Afr. J. Anim. Sci. 24, 56–60. Ominski, K.H., Kennedy, A.D., Wittenberg, K.M., Moshtaghi Nia, S.A., 2002. Physiological and production responses to feeding schedule in lactating dairy cows exposed to short-term, moderate heat stress. J. Dairy Sci. 85, 730–737. Overton, M.W., Sischo, W.M., Temple, G.D., Moore, D.A., 2002. Using timelapse video photography to assess dairy cattle lying behavior in a freestall barn. J. Dairy Sci. 85, 2407–2413. Roche, J.R., Dillon, P.G., Stockdale, C.R., Baumgard, L.H., VanBaale, M.J., 2004. Relationships among international body condition scoring systems. J. Dairy Sci. 87, 3076–3079. Roman-Ponce, H., Thatcher, W.W., Buffington, D.E., Wilcox, C.J., Van Horn, H.H., 1977. Physiological and production responses of dairy cattle to a shade structure in a subtropical environment. J. Dairy Sci. 60, 424–430. Schu¨tz, K.E., Cox, N.R., Matthews, L.R., 2008. How important is shade to dairy cattle? Choice between shade or lying following different levels of lying deprivation. Appl. Anim. Behav. Sci. 114, 307–318. Shearer, J.K., Beede, D.K., Bucklin, R.A., Bray, D.R., 1991. Environmental modifications to reduce heat stress in dairy cattle. Agri-Practice 12, 7–18. Tapkı, I˙., S¸ahin, A., 2006. Comparison of the thermoregulatory behaviour of low and high producing dairy cows in a hot environment. Appl. Anim. Behav. Sci. 99, 1–11. Tucker, C.B., Rogers, A.R., Schu¨tz, K.E., 2008. Effect of solar radiation on dairy cattle behaviour, use of shade and body temperature in a pasture-based system. Appl. Anim. Behav. Sci. 109, 141–154. West, J.W., 2003. Effects of heat-stress on production in dairy cattle. J. Dairy Sci. 86, 2131–2144. West, J.W., Mullinix, B.G., Bernard, J.K., 2003. Effects of hot, humid weather on milk temperature, dry matter intake, and milk yield of lactating dairy cows. J. Dairy Sci. 86, 232–242. Za¨hner, M., Schrader, L., Hauser, R., Keck, M., Langhans, W., Wechsler, B., 2004. The influence of climatic conditions on physiological and behavioural parameters in dairy cows kept in open stables. Anim. Sci. 78, 139–147.
Contents lists available at ScienceDirect
Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
Dairy cows prefer shade that offers greater protection against solar radiation in summer: Shade use, behaviour, and body temperature Karin E. Schu¨tz a,*, Andrea R. Rogers a, Neil R. Cox b, Cassandra B. Tucker c a
AgResearch Ltd., Agricultural Systems, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton, New Zealand AgResearch Ltd., Bioinformatics, Mathematics & Statistics, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton, New Zealand c University of California, Department of Animal Science, 1 Shields Avenue, Davis, CA 95616, United States b
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 4 July 2008 Available online 23 August 2008
There is considerable evidence that shade is a valuable resource for cattle in summer, but less is known about the important design features of effective shade. The aim of this experiment was to investigate if lactating dairy cows have a preference for shade that offers greater protection against solar radiation. Shade was provided by wooden structures covered with shade cloth that blocked 25, 50 or 99% of solar radiation. Nine groups of Holstein–Friesian cows (27 animals in total, 3 animals/group) were exposed to three treatment combinations: pair-wise simultaneous presentation of shade cloth that blocked: (1) 50 and 99%, (2) 25 and 50%, and (3) 25 and 99% of solar radiation. Cows were exposed to each combination in a cross-over design (2 d/combination). Shade use and time budgets were recorded during the hottest part of the day (10:00–17:00 h). Within each group, cows were categorised as predominantly black, white, or black and white in colour (one of each coat colour/group) in order to investigate the interaction between coat colour and treatment choice. Cows preferred shade cloth that blocked greater amounts of solar radiation in two of the combinations (99% versus 25%: 72.3% time spent in the 99% option, P < 0.001, S.E.: 3.9%; 50% versus 25%: 72.0% time spent in the 50% option, P < 0.001, S.E.: 3.5%), but showed no preference for shade cloth that blocked 50 or 99% of solar radiation when these two options were presented simultaneously (49.8% time spent in the 99% option, P = 0.509, S.E.: 5.3%). Neither coat colour nor weather conditions influenced preference for shade type. Cows spent more time in shade on days with higher solar radiation levels (P < 0.001, slope: 0.04%, S.E.: 0.01%) and higher ambient air temperature (P = 0.021, slope: 2.63%, S.E.: 0.02%). Mean body temperature increased with increasing temperature–humidity index (P = 0.014, slope: 1.9%, S.E.: 0.7%), heat load index (P = 0.009, slope: 0.6%, S.E.: 0.2%) and ambient air temperature (P = 0.065, slope: 2.1%, S.E.: 1.1%). In conclusion, cows preferred shade that provided more protection from solar radiation (50 and 99% blockage versus 25%) and showed behavioural and physiological changes associated with increased heat load. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Behaviour Body temperature Coat colour Dairy cattle Heat load Shade
1. Introduction Exposure to summer weather affects both the behaviour and physiology of cattle. Increased heat load, caused
* Corresponding author. Tel.: +64 7 838 5571; fax: +64 7 838 5038. E-mail address: [email protected] (K.E. Schu¨tz). 0168-1591/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2008.07.005
by environmental factors such as air temperature, relative humidity, wind speed and solar radiation, elicits behavioural and physiological responses, including increased body temperature and respiration rate, and reduced activity and feed intake (Hahn, 1999; Ominski et al., 2002; West, 2003; Tapkı and S¸ahin, 2006). Hot and humid weather may also negatively affect breeding performance in dairy cattle by reducing fertility (Roman-Ponce et al.,
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1977; De Rensis and Scaramuzzi, 2003). Excess heat load can in extreme cases severely compromise animal welfare and result in death (Armstrong, 1994). Cows readily use shade when given access to it and the provision of shade can alleviate negative effects of heat load (Kendall et al., 2006; Tucker et al., 2008). There is evidence that dairy cows value access to shade highly in hot weather by choosing to stand in shade over lying when deprived of lying for 12 h (Schu¨tz et al., 2008). However, little is known about which physical aspects of shade are important to cows. This knowledge is important in order to design and provide optimal shade for cattle. Various types of shade, such as trees or man-made structures, create different microclimates and studies have shown that cows prefer specific types of shade. For example, Gaughan et al. (1998) demonstrated that a single group of lactating Holstein–Friesian cows in Queensland, Australia, preferred shade created by an iron roof to shade cloth (70% blockage of solar radiation), choko vines or single trees, when given access to all types of shade simultaneously. The iron roof in the study by Gaughan et al. (1998) provided greater protection against solar radiation than the shade cloth or the choko vines, but the iron roof was also located such that it also had less solar radiation from the sides, due to shading from the other treatments. Thus, it is possible that the interaction between location and shade type influenced the preference for the iron roof. Others have reported that cows prefer shade created by trees rather than man-made structures due to the efficiency in blocking solar radiation and evaporation from leaves, which cools the surrounding air (e.g. Shearer et al., 1991). Trees, however, can have a short life-span in pastures with large dairy herds (Shearer et al., 1991) and, therefore, provision of other shade types may be more practical. Tucker et al. (2008) demonstrated that dairy cows with access to shade that provided more protection from solar radiation spent more time using this resource than cows with access to shade that provided less protection. All cows spent more time in the shade on days with higher levels of solar radiation and within a day, shade use peaked when solar radiation levels were highest. In addition to ambient conditions, some previous studies have demonstrated that coat colour can influence the response to heat; dark-coated animals are more sensitive to heat stress (e.g. Finch, 1984; Brown-Brandl et al., 2006a). In contrast, Tucker et al. (2008) found that darker coloured cows used shade less than lighter animals when shade blocked 99% of solar radiation, creating an unclear picture of how coat colour affects shade use and response to heat load. The aim of this study was to investigate dairy cattle preferences for shade offering greater protection from solar radiation. In addition, this study aimed to describe the effects of coat colour, body temperature and weather conditions on these preferences. It was predicted that cows would prefer shade that offered greater protection from solar radiation and that these preferences would be pronounced on hot days, particularly if body temperature was high or if cows had dark coats.
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2. Materials and methods 2.1. Animals and treatments All procedures involving animals were approved by the Ruakura Animal Ethics Committee under the New Zealand Animal Welfare Act 1999. The study utilised 27 Holstein–Friesian dairy cows in mid-lactation that ranged from 4 to 9 years of age and were 193 22 (mean S.D.) d in milk at the start of the experiment. They weighed 510 43 kg (mean S.D.) and had a body condition score between 4 and 5 on a 1–10 scale (Roche et al., 2004). All cows utilised in this study had been used previously in the study by Tucker et al. (2008). All cows were accustomed to the shade structures and to the presence of observers. Previous experience with each shade type was balanced in this experiment. The cows were milked twice daily (approximately at 06:30 and 14:00 h). Cows were categorised as predominantly black (96 3% black hair), white (25 8% black hair), or black and white (60 7% black hair). The percentage of black hair was estimated from digital photographs of both sides of each cow using image analysis software (Scion Image v.4.0.2, Scion Corporation, Frederick, USA). The animals were tested as 9 groups (3 cows/group, n = 9) at the AgResearch Number 1 and 2 Dairies near Hamilton, New Zealand (latitude 378470 S, longitude 1758190 E). The groups of cows were balanced for coat colour category (one of each: black, black and white, and white cow in each group). Shade cloth (Donaghys Industries Ltd., Christchurch, New Zealand) that blocked either 25, 50 or 99% of solar radiation was presented in a pairwise manner, resulting in three treatment combinations: (1) 50 and 99% solar radiation blocked, (2) 25 and 50% solar radiation blocked, and (3) 25 and 99% of solar radiation blocked (n = 9 groups/combination, Fig. 1). Pairwise presentation was used to assess the relative ranking of each type of shade. Groups were rotated through these three treatment combinations in a balanced cross-over design (2 d/combination). The shade cloth was mounted onto wooden structures. Each group was provided with 4 wooden shade structures, two of each level of protection from solar radiation (Fig. 1). To prevent any overlap in shade cast, there was a distance of 10 m between each structure. Each structure provided a shaded area of 12 m2 (total shade area: 48 m2, 16.0 m2 of shade/cow) and had a 1 m section of the legs painted at 1–2 m height (99, 50, 25%; green, red, yellow respectively) in order to facilitate observations and provide the animals with a visual cue for the 3 types of shade cloth. All structures had a mown patch of grass (3.5 m 4.5 m) beneath them in order to minimise grazing activities in the shaded area. Each structure also had a rectangle perimeter of 3 m 4 m identified clearly with white paint directly beneath the structure. Both the mowed patch of grass and painted rectangle facilitated behavioural observations. The cows always had access to a water trough located 7–10 m away from the structures. Three groups were tested simultaneously for 6 d, 2 d in each treatment combination, with one of each of the combinations tested at the same time for a total of 18 d of testing during February and March 2006 (southern hemisphere summer). Cows were moved into the treatment areas at approximately 08:00 h where they had access to the shade structures until approximately 17:30 h. A fresh sward of grass was provided at approximately 08:00 h each day. Following completion of observations, all cows were moved onto a pasture without the shade structures, adjacent to the treatment area, where they spent the night and were provided with another fresh sward of grass. This strategy minimised the number of times the shade structures were moved because fresh grass was also provided in a separate area. 2.2. Environmental measurements Weather measurements (ambient air temperature, relative humidity, wind speed, rainfall, solar radiation and black globe temperature) were recorded and the temperature–humidity index (THI) and heat load index (HLI) were calculated at 10 min intervals during the 18 d trial as reported by Tucker et al. (2008). All weather measurements were taken in a field adjacent to the observation area (2 m away). The microclimate (air temperature, black globe temperature and relative humidity) beneath the 3 types of shade cloth and in an adjacent control pasture (no shade) was recorded at 10 min intervals with HOBO Pro Dataloggers (Onset Computer Corporation, Bourne, MA, USA) between 10:00 and 17:00 h during the 18 d of data collection. 2.3. Behavioural measurements Time budgets and shade use were recorded using instantaneous scan sampling (Martin and Bateson, 1993) every 10 min during the hottest part
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Fig. 1. Diagram of the treatment areas. Groups of cows (one black, black and white, and white cow/group) were offered two types of shade per treatment combination (25 or 50%, 25 or 99%, 50 or 99%).
of the day (10:00–17:00 h) on all 18 d of testing. The observations were interrupted by milking between 14:00 and 15:00 h (milking lasted 68 10 min, mean S.D.). The groups were observed for 2 h after returning from milking, i.e. all groups were observed for 6 h each day. Each replicate (3 groups of cows tested at the same time, one of each treatment combination) was observed simultaneously by trained staff (multiple observers were used to collect the behavioural information). Time budget information was recorded for lying, standing, and grazing. Cows were considered lying if their flank was in contact with the ground and standing was defined as not lying. Cows were considered to be grazing if grass was being ingested or could be seen in the mouth. The use of the shade structures was measured in two ways as described in Tucker et al. (2008): if at least one hoof was within/on the painted rectangle directly underneath the shade structure and/or at least one hoof was within the shadow cast by the structure. The second measurement was only taken when the outline of the shadow cast by the structure was clearly defined. Both measures were used because recording only the latter would likely underestimate shade use when the shadow was not clearly defined. Cows were identified with coloured collars and paint on the rump (Tell tail paint, FIL NZ Ltd., Mount Maunganui, New Zealand). Inter-observer reliability, as measured by percentage agreement, was between 96 and 100% for all behaviours. Interobserver agreement was lowest when assessing time spent grazing. 2.4. Body temperature Internal body temperature was recorded every 10 min using a modified vaginal controlled internal drug release insert (CIDRTM; InterAg, Hamilton, New Zealand) fitted with a microprocessor-controlled MinilogTX data logger (Vemco Ltd., Shad Bay, Nova Scotia, Canada). Temperature loggers were inserted into the vaginal cavity for the 6 d of testing. One temperature logger of a white cow malfunctioned and therefore data from 26 of the 27 cows were used in the analysis of body temperature. 2.5. Statistical analysis All data were averaged daily across the observation period for each treatment combination (10:00–17:00 h, 18 d in total). The results regarding shade use were the same regardless of whether shade use was estimated with the measure ‘‘standing in shadow cast by the structure’’ or ‘‘standing directly under the structure.’’ Therefore, a combination of the two measures was used (total shade use) and is presented throughout the rest of this paper. The proportions of total shade use, preference for shade type (proportion of time spent using the shade cloth that blocked more solar radiation), behaviours (grazing, lying, standing, and standing without grazing), and mean daily body temperature were analysed in a Generalised Linear Mixed Model (GLMM) in GenStat with random effects of group, day, animal, day by animal interaction and interactions between group and treatment combination. The fixed effects included coat colour, treatment
combination, and coat colour by treatment combination interaction. The GLMM allows modelling of the correlation structure arising from correlated behaviour of animals within a group, repeat measurements on the same animals, on the same days etc., while maintaining the appropriate distributional assumptions (in this case, binomial). To estimate the slope of the relationship between response variables and THI, HLI, ambient air temperature and solar radiation, response variables were averaged across the 3 cows for each group and day. In addition, the slope was calculated for the relationship (across animals) between body temperature measures [mean, minimum, maximum, amplitude (maximum minimum) during the 6 h observation period] and both shade use and preference for shade type on each day (9 points/d were used to generate slopes).
3. Results 3.1. Environmental conditions Air temperature, black globe temperature, wind speed, humidity, rain fall and solar radiation recordings during the trial and calculated THI and HLI values are summarised in Table 1. Ambient temperature, solar radiation, HLI and THI are all measures of heat load. We present relationships with all four of these weather variables to facilitate comparisons with other papers. 3.2. Shade use and behaviour In this study, shade was clearly defined on all four sides of the shadow cast by the structure in 45 33% (mean S.D.) of the scan samples per day, range 0–100%/d. When shade cloth that blocked 25 and 99% of solar radiation were provided simultaneously, the cows preferred the shade cloth that blocked more solar radiation (72.3% time spent in 99% option, P < 0.001, S.E.: 3.9%, Fig. 2). When shade cloth that blocked 25 and 50% of solar radiation were provided simultaneously, the cows again preferred the shade cloth that blocked more solar radiation (72.0% time spent in the 50% option, P < 0.001, S.E.: 3.5%, Fig. 2). The cows did not show any preference for shade cloth that blocked 50 or 99% of solar radiation when these were presented simultaneously (49.8% time spent in the
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Table 1 Summary of meteorological records for the 18 d of testing in summer during the observation period (10:00–17:00 h) and over 24 h Weather variable
Temperature (8C) Black globe temperature (8C) Relative humidity (%) Solar radiation (W/m2) Wind speed (km/h) Rainfall (mm/d) THIa HLIb
No shade (24 h)
No shade day-time (10:00–17:00 h)
25% blockage (10:00–17:00 h)
50% blockage (10:00–17:00 h)
99% blockage (10:00–17:00 h)
Mean
Range
Mean
Range
Mean
Range
Mean
Range
Mean
Range
16 17 72 218 6 2 59 53
1–24 0–33 32–94 0–1171 0–27 0–9 35–72 35–100
20 24 58 582 11 0 65 62
13–24 15–33 32–92 36–1171 0–27 0–2 56–72 42–98
20 23 63 n/a n/a n/a 66 n/a
14–24 15–34 31–100 n/a n/a n/a 56–75 n/a
20 22 64 n/a n/a n/a 66 n/a
14–25 14–31 32–100 n/a n/a n/a 57–72 n/a
20 21 64 n/a n/a n/a 66 n/a
14–24 14–26 35–100 n/a n/a n/a 57–72 n/a
The measurements were taken in a nearby pasture without any shade and underneath each shade cloth blocking different amount of ambient solar radiation (25, 50 and 99%). Both mean values and ranges (minimum to maximum) are presented. a Temperature–humidity index. b Heat load index.
Fig. 2. Average preference for shade type that blocked more solar radiation (indicated in bold on x-axis label). Bars are the group mean and each symbol represents one cow of each coat colour: predominantly black, white, or black and white (b/w).
99% option, P = 0.509, S.E.: 5.3%, Fig. 2). No interaction between preference for shade type and coat colour was found (P 0.419). None of the measured weather variables (solar radiation, ambient air temperature, THI or HLI) had any influence on preference for shade type (P 0.272).
The cows, on average, used shade during 29.8% (range: 0–64.9%) of the observation period per day, which corresponds to 1.8 h with a range of 0–3.9 h/6 h observation. Cows spent more time in shade on days with higher solar radiation levels (P < 0.001, slope:
Fig. 3. Total shade use (h/6 h of observations) by dairy cows between 10:00 and 17:00 h on days with different levels of solar radiation. Each point is an average of nine cows (S.E.M.) per day.
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Fig. 4. Total shade use (h/6 h of observations) by dairy cows between 10:00 and 17:00 h on days with different ambient air temperature. Each point is an average of nine cows (S.E.M.) per day.
Table 2 The behaviour and total shade use (mean S.E.D.) of cows with different coat colour (predominantly black, white, or black and white, one coat colour/group, n = 9 groups) between 10:00 and 17:00 h (interrupted by 1 h of milking between 14:00 and 15:00 h) on pasture in summer Behaviour (h/6 h of observation)
Lying Grazing Standing, not grazing Shade use
Coat colour Black and white
Black
White
0.1a 2.7 3.0 1.3
0.1a 2.8 3.0 1.8
0.2b 2.7 2.9 1.7
S.E.D.
P-value
0.09 0.23 0.26 0.38
0.050 0.870 0.805 0.312
Superscripts of different letters indicate a significant difference.
0.04%, S.E.: 0.01%, Fig. 3) and higher ambient air temperature (P = 0.021, slope: 2.63%, S.E.: 0.02%, Fig. 4). This pattern was also apparent with THI (P = 0.085, slope: 1.36%, S.E.: 0.8%), but not with HLI (P = 0.144, slope: 0.36%, S.E.: 0.3%).
Time budgets of cows with different coat colours are summarised in Table 2. Time spent on lying, grazing or standing without grazing during the observation period was not affected by solar radiation, air temperature, THI or HLI (P 0.271).
Fig. 5. Relationship between body temperature (mean, minimum and maximum values) and temperature–humidity index (THI), heat load index (HLI), air temperature and solar radiation of dairy cows observed between 10:00 and 17:00 h. Each point is the mean body temperature of nine cows per day.
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3.3. Body temperature during the observation period (10:00–17:00 h) Body temperature changed in response to weather conditions (Fig. 5). Cows had higher mean body temperature with increasing THI (P = 0.014, slope: 1.9%, S.E.: 0.7%), HLI (P = 0.009, slope: 0.6%, S.E.: 0.2%) and ambient air temperature (P = 0.065, slope: 2.1%, S.E.: 1.1%). Cows also had higher maximum body temperature with increasing air temperature (P = 0.020, slope: 4.1%, S.E.: 1.7%), THI (P = 0.004, slope: 3.5%, S.E.: 1.2%) and HLI (P = 0.004, slope: 1.1%, S.E.: 0.4%) and with decreasing solar radiation (P = 0.023, slope: 0.04%, S.E.: 0.02%). Furthermore, cows had higher amplitudes in body temperature (maximum – minimum) with increasing THI (P = 0.038, slope: 3.3%, S.E.: 2.3%) and HLI (P = 0.067, slope: 0.9%, S.E.: 0.5%) and with decreasing solar radiation (P = 0.012, slope: 0.06%, S.E.: 0.02%). There was no statistically significant relationship between minimum body temperature and any weather variables (P 0.261). 4. Discussion Dairy cattle preferred shade that offered protection against 50 and 99% of solar radiation over shade cloth that blocked only 25% of solar radiation. There were small differences in THI beneath the types of shade, whereas the black globe temperature, which incorporates the effects of solar radiation, decreased by 1 8C per 25% blockage. This suggests that the cows preferred the more protective shade cloth based on differences in solar radiation or ambient temperature, rather than other factors. These findings are in accordance with the results of Tucker et al. (2008) who demonstrated that cows spend more time under shade cloth that blocked more solar radiation. There were no preferences for shade cloth that blocked either 50 or 99% solar radiation when offered simultaneously. There are at least two possible reasons for this. Firstly, the dairy cows may not be able to distinguish between the shade cloth blocking 50 and 99% of solar radiation. This explanation however, is not supported by the findings in other studies. Tucker et al. (2008) found that cows spent more time in shade that offered greater protection against solar radiation, although the difference in shade use between 50 and 99% was smaller (0.3 h/15.5 h or 9% difference in shade use) than the difference between 99 and 25% (2.0 h/15.5 h or 60% difference in shade use). Furthermore, Bennett et al. (1984/1985) demonstrated that shorthorn steers preferred shade cloth that blocked 80% of solar radiation over 50 and 70%, whereas there was no significant difference in shade use between the 50 and 70%. Thus, cattle can distinguish between shade differing by 10% in protection from solar radiation, a value smaller than the 49% difference between the options presented in the current experiment. Secondly, the microclimate beneath the shade blocking 50 and 99% of solar radiation may have provided equal cooling opportunities in the weather conditions during the trial (air temperature was never above 25 8C). It was on average 1, 2 and 3 8C cooler underneath the 25, 50 and 99% options respectively compared to the area without shade.
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These differences are difficult to interpret as there is no information on whether 22 8C (50% blockage) and 21 8C (99% blockage) provide similar cooling opportunities in 24 8C ambient conditions from the animal’s point of view. The literature in this area can be broadly categorised in two ways. The first type of study defines thresholds for when weather conditions are problematic for cattle either before the study (Brown-Brandl et al., 2005) or from their dataset (Muller et al., 1994; Fisher et al., 2002). Other studies describe the nature of the relationship between shade use (or other measures of heat load) and ambient conditions (Tucker et al., 2008). The results from these studies are variable and often highly dependent on local conditions. Further research is needed to understand how preference for different shade types is affected by weather variables, particularly during more extreme weather conditions. Indeed, previous research in the same area found that dairy cows increased their use of shade when ambient temperatures exceeded 25 8C (Fisher et al., 2002). Although average ambient air temperature was 20 8C during observations in the current trial (range: 13–24 8C) the cows readily used shade. Use of shade when ambient conditions are below 25 8C may play a role in thermoregulation, that is, these behavioural changes may help prevent the dramatic increase in panting that has been reported for beef cattle when temperatures rise above 25 8C (Brown-Brandl et al., 2006b). However, there may also be other reasons for cattle to use shade, such as avoidance of the harmful effects of solar radiation on skin and eyes. Little is known about the motivation for shade seeking behaviour and mechanisms underlying shade use could be an interesting area for future work. Cows spent more time in shade on days with higher levels of solar radiation and air temperature. Similar results have been found by others; for example Tucker et al. (2008) also found a positive relationship between shade use and ambient solar radiation. Furthermore, Bennett et al. (1984/1985) reported that steers of several beef breeds spent more time in shade as ambient temperatures and solar radiation levels increased. In the current study, cows spent more time in shade with increasing air temperature even though air temperature and THI never reached levels previously reported to have negative effects on the physiology and production of dairy cattle (air temperature of 25 8C, THI of 72, e.g. Muller et al., 1994; West et al., 2003). There is evidence that cooling dairy cows with shade or sprinklers lowers their body temperature when THI equals 67 (Kendall et al., 2007), which suggests that dairy cows benefit from cooling opportunities under a wider range of ambient conditions than previously reported. Cattle seek shade in response to increased heat load. Other behavioural responses to increased heat load include a reduction in time spent lying and grazing (Overton et al., 2002; Za¨hner et al., 2004; Tucker et al., 2008). It has been suggested that cattle stand as a way to maximise the surface area exposed to the environment and increasing the airflow around the body (e.g. Ansell, 1981). In this study, behavioural changes were in general not found. However, light coloured cows spent more time lying than dark-coloured cows, which suggests that the cows with
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predominantly white coats were less affected by warm weather. Dark-coloured cattle are thought to be more sensitive to heat stress than light coloured cattle (e.g. Hansen, 1990; Gaughan et al., 1998; Brown-Brandl et al., 2006a). However, neither shade use nor body temperature measurements in this study provided any support for this idea. It is possible that dark-coloured cows change their behaviour earlier than lighter coloured cows in response to increased heat load in order to thermoregulate, for example by reduced lying times. Thus, differences in thermoregulatory behaviour could explain the similarity in body temperature between predominantly black and white cows. Mean body temperature between 10:00 and 17:00 h increased with increasing THI and HLI. In addition, maximum body temperature increased and the amplitude in body temperature (maximum–minimum) was greater with increasing air temperature, THI, and HLI. Similar findings have been reported by others including Muller et al. (1994) and Kendall et al. (2007). 5. Conclusions Dairy cows exhibited both behavioural and physiological changes in response to warm weather, including increased body temperature and shade use. Cows showed clear preferences for shade that offered greater protection from solar radiation. The cows readily used the shade even on cool days, which suggests that shade is an important resource during summer. Acknowledgements The authors gratefully acknowledge the technical assistance from AgResearch staff: Kate Brown, Katie Carnie, Antonia Davies, Debbie Davison, Suzanne Dowling, Cara Hansen, Frankie Huddart, Paul Kendall and Haley Shepherd. We also thank the staff at AgResearch No. 1 and 2 Dairies, Ron Clarke, Bob Smith and Kevin Orr. This work was funded by the Foundation for Research, Science and Technology. References Ansell, R.H., 1981. Extreme heat stress in dairy cattle and its alleviation: a case report. In: In: Clark, J.A. (Ed.), Environmental Aspects of Housing for Animal Protection. Butterworths, London, United Kingdom, pp. 285–306. Armstrong, D.V., 1994. Heat stress interaction with shade and cooling. J. Dairy Sci. 77, 2044–2050. Bennett, I.L., Finch, V.A., Holmes, C.R., 1984/1985. Time spent in shade and its relationship with physiological factors of thermoregulation in three breeds of cattle. Appl. Anim. Behav. Sci. 13, 227–236. Brown-Brandl, T.M., Eigenberg, R.A., Nienaber, J.A., Hahn, G.L., 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle. Part 1. Analyses of indicators. Biosyst. Eng. 90, 451–462.
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