J. Dairy Sci. 2007. 90:3671-3680. doi:10.3168/jds.2006-766
© 2007 American Dairy Science Association ®
Sprinklers and Shade Cool Cows and Reduce Insect-Avoidance Behavior in Pasture-Based Dairy Systems
P. E. Kendall*,
G. A. Verkerk
,
J. R. Webster* and
C. B. Tucker*,
,1
* Animal Behavior and Welfare, AgResearch Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand
Dexcel Ltd., Private Bag 3221, Hamilton, New Zealand
Department of Animal Science, University of California, Davis 95616-8521
1 Corresponding author: cbtucker{at}ucdavis.edu
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ABSTRACT
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The body temperature of dairy cows in pastoral systems during summer reaches a peak during and following the p.m. milking. Shade and sprinklers can be used separately or in combination at the milking parlor to reduce heat load. Farmers anecdotally report that the use of sprinklers reduces irritation from insects that occurs while cows are waiting for milking. Once daily, we assessed the effectiveness of short-term exposure to shade and sprinklers for cooling cows [via respiration rate and body (vaginal) temperature] and reducing insect-avoidance behaviors before the p.m. milking in a pasture-based dairy system. Head position was measured as an indicator of whether cattle were avoiding water from the sprinklers. Forty-eight Holstein-Friesian dairy cows were divided into 12 groups (4 cows per group, n = 3 groups/treatment) and were exposed to 1 of 4 treatments for 90 min before the p.m. milking: 1) shade, 2) sprinklers, 3) shade and sprinklers, or 4) uncooled control. Respiration rate was reduced by 30% with shade alone compared with controls [54 vs. 78 ± 2.3 ( ± SED) breaths/min, respectively]. Sprinklers alone (30 ± 2.3 breaths/min) and the combined effects of shade and sprinklers (24 ± 2.3 breaths/min) reduced the respiration rate by 60 and 67%, respectively, compared with controls. Shaded cows had lower body temperatures during the 90-min treatment period compared with controls (shade: 38.6 ° C; shade and sprinklers: 38.6 ° C; control: 38.9 ± 0.09 ° C). The decrease in body temperature of cows under sprinklers was more marked than for shade alone and remained lower for at least 4 h after milking (sprinklers: 38.7 ° C; shade and sprinklers: 38.6 ° C; shade: 38.9 ° C; control: 39.2 ± 0.10 ° C). The sprinkler treatment reduced the number of tail flicks (control: 12.6 vs. sprinklers: 6.6 ± 2.4 flicks/min) and hoof stamps (control: 4.4 vs. sprinkler: 2.2 ± 0.5 stamps/min). Cows exposed to sprinklers spent more time with their heads lowered compared with cows in the shaded and control treatments. The reductions in body temperature and respiration rate attributable to shade and sprinklers were greatest when the temperature-humidity index and heat-load index were 
69 and 77, respectively, and cows benefited from cooling when these levels were exceeded.
Key Words: heat stress • respiration rate • body temperature • thermoregulation
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INTRODUCTION
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An increasing proportion of milk products on the global market originate from pasture-based farming systems (FAO, 2004). Consumer demand for organic milk products is growing and some organic standards, including those used by the USDA’s National Organic Program, require that cows spend no less than 120 d/yr on pasture (National Organic Standards Board, 2005). This reflects a growing perception that pasture-based systems are beneficial to dairy cattle welfare compared with barn-housed systems. A consequence of pasture-based dairy systems is that cows are exposed to extremes of weather. Hot weather, in particular, can decrease milk production, compromise reproductive performance, and impair animal welfare.
The respiration rate and body temperature of lactating cows increases during acute heat exposure (Ominski et al., 2002; Spiers et al., 2004), and cows with dark-colored coats are more susceptible to heat than cows with light-colored coats (Hansen, 1990). Cows provided with access to shade while on pasture have a lower body temperature than those without shade (Davison et al., 1988). Recently, we found that dairy cows readily used shade when it was provided and produced an additional 0.5 kg of milk/d than cows without access to shade (Kendall et al., 2006). Regardless of access to shade, all cows reached a similar maximum body temperature after walking to the parlor for the p.m. milking. Cooling cows with both fans and sprinklers for 20 to 30 min after they walked to the milking parlor reduced both body temperatures and respiration rates in the short term (Valtorta and Gallardo, 2004). Furthermore, use of fans and sprinklers just prior to milking reduced body temperature for 2 to 4 h after milking compared with cows that received no cooling at the parlor (Araki et al., 1985). Collectively, these results suggest that cooling cows before the p.m. milking could be a practical and effective way to reduce the peak body temperature and respiration rate of cows in pastoral farming systems.
Both shade and sprinklers are practical methods for cooling cows while they are waiting to be milked, but little is known about the effectiveness of providing a single daily short-term (e.g., 90-min) exposure to these cooling methods. We chose to explore these options, in part, because 40% of farmers in New Zealand already use sprinklers to cool their cows before the p.m. milking (Tucker et al., 2005), and guidelines are needed about the weather conditions in which sprinklers and shade should be provided.
Farmers anecdotally report that sprinklers reduce irritation from insects while cows are waiting to be milked. Little is known about the behavioral responses, such as fly avoidance and other behavioral changes, associated with exposure to sprinklers. In winter, cows seek shelter, particularly when it is raining (Vandenheede et al., 1995), and when exposed to wind and rain, they are 5 times more likely to stand with their heads lowered compared with their sheltered counterparts (Tucker et al., 2007). Thus, head position may indicate whether cattle find sprinklers aversive and whether this aversion is related to weather conditions.
Our objective was to assess the effects of shade and sprinklers, alone or in combination, on the physiological and behavioral responses of pasture-based dairy cows with different coat colors. Our specific interest was in the effectiveness of these cooling methods when applied only before the p.m. milking. Finally, the responses were evaluated over a range of summer conditions in a temperate climate to identify when cooling methods should be used.
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METHODS AND MATERIALS
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Experimental Design and Management of Cows
All procedures were approved by the Ruakura Animal Ethics Committee in accordance with the New Zealand Animal Welfare Act 1999. All values presented in this section are mean ± SD. Forty-eight mixed-age (2 to 11 yr) Holstein-Friesian dairy cows in midlactation (175 ± 21 DIM) were used. The cows had an initial BW of 482 ± 49 kg and BCS between 3.5 and 5 on a scale of 1 to 10 (Roche et al., 2004). The coat color was determined from digital photographs of both sides of each cow using image analysis software (Scion Image version 4.0.2, Scion, Frederick, MD). Cows were categorized as either predominantly black (89 ± 6% black hair, mean ± SD) or both black and white (mixed; 67 ± 8% black hair).
The cows were allowed to graze as a single herd at a research farm in Hamilton, New Zealand (latitude 37 ° 47' S, longitude 175 ° 19' E) in January and February (southern hemisphere summer). Each day, at approximately 1230 h, the cows were walked (590 ± 316 m, single journey) to a holding pen adjacent to the milking parlor and separated into 12 treatment groups (4 cows per group). These groups were balanced for milk production and coat color category (2 black and 2 black and white cows in each group) and were assigned 1 of 4 treatments: 1) shade, 2) sprinklers, 3) shade and sprinklers, or 4) uncooled control. Treatments were applied for approximately 90 min/d (81 ± 8 min/d) prior to milking, which occurred between 1430 and 1530 h, for 35 consecutive days. One day of observation was omitted because of heavy rainfall.
During the 90-min treatment period, each group was kept in a 2.5 x 2.5 m pen. The space allowance for each group was approximately 1.25 m2/cow. This level of stocking density simulated normal conditions in holding pens before milking. Cows in the control treatment had no shade or sprinklers. The shade treatment consisted of a 2.5-m-high structure (3 x 3 m) with a double thickness of shade cloth on the roof that excluded > 93% of UV light, and with 3 of the sides covered with a single layer of shade cloth. The sprinkler treatment was created with an oscillating sprinkler fixed 1.9 m above the ground (approximately 0.5 m above the cows) that delivered approximately 75 ± 74 mm of water/h (water temperature: 22 ± 1 ° C). Cows in the sprinkler-only treatment had no protection from the sun. All cows were treated with a fly repellent and insecticide (Blaze, Schering-Plough Animal Health Ltd., Wellington, New Zealand) twice during the course of the experiment.
Sampling and Measurement
Air temperature, relative humidity, wind speed, solar radiation, and rainfall were recorded at 10-min intervals using a portable weather station (Campbell Scientific, Scott Technical Instruments Ltd., Hamilton, New Zealand) located in a pastured area adjacent to the holding pens. The microclimate in each treatment area was measured with these weather stations in the days following the experiment. Temperature-humidity index (THI) and heat-load index (HLI) were used as composite measures of thermal comfort and were calculated as reported previously (Kendall et al., 2006).
Body temperature was measured over 7-d periods at 10-min intervals in 3 cows in each group (2 black and white cows and 1 black cow) with a modified vaginal controlled internal drug release insert (InterAg, Hamilton, New Zealand) fitted with a microprocessor-controlled data logger (Minilog TX, Vemco Ltd., Shad Bay, Nova Scotia, Canada). Thus, throughout this experiment, the term "body temperature" refers to vaginal temperature. Temperature loggers were inserted into the vaginal cavity on a 7-d in and 3-d out cycle to minimize irritation. This schedule resulted in 25 d of body temperature measurements in total. Respiration rate (flank movements/30 s) was recorded before treatments were applied in a subset of cows (n = 24, same cows on all days after the walk to the parlor) and in all cows after the 90-min treatment period.
The frequency of tail flicks (defined as the number of times the tail crossed the midline of the leg) and hoof stamps (defined as the number of times any hoof was lifted off the ground) were recorded continuously for 30 s approximately every 12 min for 60 min during the 90-min treatment period, for a total of 150 s of observations/cow per day. Head position was recorded before and after each of these 30-s sessions using instantaneous scan sampling (Martin and Bateson, 1993) and was categorized as either low (chin below the brisket), high (poll above the wither), or middle (between low and high). Over the course of the experiment, 11 observers recorded respiration rate and behavioral traits. Interob-server agreement was calculated as the percentage of agreement and was 96% for respiration rate, 95% for tail flicks, 83% for hoof stamps, and 93% for head position. Although respiration rate and behavioral traits were measured over 30-s periods, the results are expressed on a per minute basis to facilitate comparison with other studies.
Finally, daily milk production was measured at the a.m. and p.m. milkings, and a pooled milk sample was collected twice weekly to determine the percentages of fat, CP, and lactose using an infrared milk analyzer (FT120; Foss Electric, Hillerød, Denmark). Milk production from the a.m. milking was considered separately, because longer term (after the p.m. milking) effects of the treatment were more likely to be detected at that time. Somatic cell count was measured on the same twice-weekly samples using an automated cell counter (Fossomatic 5000; Foss Electric).
Statistical Analyses
The effects of shade and sprinklers were tested with a 2 x 2 design (4 treatments of shade, sprinklers, a combination of shade and sprinklers, and uncooled controls). The group served as the experimental unit. Data were averaged across the collection period for each treatment (25 d for body temperature; 34 d for behavior, milk production, and respiration rate). For body temperature, data were divided into four 2-h time blocks (1050 to 1240, 1250 to 1440, 1450 to 1640, and 1650 to 1840 h) for analysis of treatment differences, and 3-h time blocks (0010 to 0300, 0310 to 0600, . . . 2110 to 0000 h) to look at daily differences in body temperature among treatment groups. Somatic cell counts were log10 transformed to normalize the distribution. The effect of treatment (shade, sprinklers, shade by sprinkler interaction, 1 df each) was tested against the group term (8 df) and the effects of coat color category (percentage of black or mixed; interactions of coat color x shade, coat color x sprinklers, and coat color x shade x sprinklers, 1 df each) were tested against the cow term (32 df) in either GenStat version 8.1 (Payne, et al., 2005) or SAS version 9.1 (SAS Institute, 1999). For all measures of milk production and composition, a covariate was used to correct for lactational performance before the start of the experiment, and inclusion of these covariates reduced the error to 7 df for the group term and 31 df for the cow term. The influence of weather on the response to treatment was assessed by using daily information from each cow to calculate the slope of the relationship between the response variable (body temperature, respiration rate, and behavior) and THI and HLI variables during the 90-min treatment period. The slopes were compared in the same model as described above. The effect of weather on milk production was explored by calculating the partial regression slopes of the relationship between daily milk yield (defined as the p.m. and following a.m. milk sample) for each cow and the THI or HLI for the day of the p.m. milking. For this analysis, weather information from the 24 h before milking was used. A linear adjustment was made for the effect of time (days) to allow for the declining milk production and treatment differences analyzed by the model described above. The influence of weather on body temperature and respiration rate responses to the treatments were investigated by visually inspecting Figure 1
to identify the threshold values for THI and HLI levels when sprinklers, shade, or both should be used (intersection between regression lines). Regression lines intersected only in the body temperature figure; thus, the model described above was repeated using only body temperature and data from days when THI was < 69 (7 d) and HLI was < 77 (9 d), respectively.
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RESULTS
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Environmental Conditions
The shade alone, sprinklers alone, and shade and sprinklers combined treatments were 0.9, 1.9, and 2.6 ° C cooler ( ± 0.6 ° C, SD), respectively, than the control treatment areas. Relative humidity was 4.3, 9.0, and 15.8% higher ( ± 3.8%, SD) in the shade alone, sprinklers alone, and shade and sprinklers combined treatments compared with the control treatment areas. Treatments with shade (alone or in combination) had 0.4 ± 0.4 km/h less wind than the control area. Temperature-humidity index and HLI were highest in the control treatment and lowest in the shade and sprinklers combined treatment. The THI was 68.8, 68.5, 67.1, and 65.9 for the control, shade, sprinklers, and shade and sprinkler treatments, respectively. The HLI was 82.3, 78.6, 79.2, and 59.8, respectively.
Table 1 summarizes the weather variables recorded during the experiment. During the 90-min treatment period (approximately 1300 to 1430 h), air temperature, solar radiation, THI, and HLI were within ranges comparable to those for 24-h mean records. Relative humidity and wind speed appeared lower during the 90-min treatment period than in the 24-h means. January and February mean air temperatures were 0.5 and 1.0 ° C, respectively, above the monthly averages for 30-yr meteorological records, whereas relative humidity and wind speed were below the 30-yr averages (Table 1). Total rainfall over the 35-d experiment was 50 mm, 48% below the 30-yr averages. The mean times for sunrise and sunset over the duration of the experiment were 0630 and 2040 h, respectively.
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Table 1. Summary of daily (24-h) and experimental period (90-min) meteorological records during the 35 d of the experiment compared with 30-yr averages (1975 to 2004) in January and February 2005 (summer in the southern hemisphere) in Hamilton, New Zealand
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Respiration Rate
The respiration rate before the start of the 90-min treatment period was 72 ± 21 breaths/min. The shade treatment reduced the respiration rate by 30%, and the sprinkler treatment reduced the rate by 60% compared with uncooled controls (Table 2) during the 90-min treatment period. The combination of sprinklers and shade was the most effective treatment in reducing the respiration rate (67%) compared with controls (Table 2). The respiration rate increased (P 
0.014) as THI and HLI increased, and the greatest increases were in control cows, followed by cows with shade alone (analysis of slopes, Figure 1
). Coat color had no influence (P 0.147) on this response to THI and HLI. There were no statistically significant differences in average respiration rate associated with coat color in response to the treatments (interaction of coat color category and shade, P = 0.086). Black cows had respiration rates of 82 breaths/min compared with 72 ± 2.3 breaths/min for cows with black and white coats in the control treatment. Black cows had respiration rates of 50 breaths/min in response to shade compared with 58 ± 2.4 breaths/min for cows with black and white coats (P = 0.086).
Body Temperature
Before the start of the 90-min treatment period, there was no difference in body temperature between groups (Table 3). Shade lowered (P = 0.006) body temperature by 0.3 ° C during the 90-min treatment period compared with control cows. The body temperature of cows treated with shade alone began to increase between 2 and 4 h after the 90-min treatment period, but remained 0.3 ° C lower (P = 0.032) than in control cows, whose body temperature continued to rise. Sprinklers tended to decrease (P = 0.093) the body temperature by 0.2 ° C during the 90-min treatment period compared with control cows, and remained constant but still lower (P < 0.001) than control and shaded cows 2 to 4 h after the start of the 90-min treatment period. For cows treated with sprinklers, body temperature reached its lowest level during the afternoon 36 ± 12 min after sprinklers were turned off. The combination of shade and sprinklers reduced the magnitude of the rise in body temperature during the 90-min treatment period and 2 to 4 h after the cooling treatment, more than in cows under shade or sprinklers alone (P = 0.042). Peak body temperatures occurred in all groups between 1610 and 1650 h each day (Figure 2). There were no interactions between shade and sprinklers on body temperature at any time of day except during the 90-min treatment period (P = 0.042). The shade treatment had no long-term effect on body temperature after 1800 h compared with control cows, although wetting cows with sprinklers tended (P 0.065) to reduce their body temperature until 0000 h (approximately 10 h after the cooling treatment had finished) relative to cows in the control and shade groups (sprinklers: 38.5 ° C; shade: 38.6 ° C; control: 38.6 ± 0.07 ° C). Coat color did not influence the response of body temperature to any treatment.
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Table 3. Mean body temperature (minimum and maximum in parentheses) of cows during 2-h blocks before, during, and after a cooling treatment that occurred before the p.m. milking1
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Figure 2. Circadian body temperature rhythms in uncooled control cows or cows provided with shade, sprinklers, or a combination of shade and sprinklers for 90 min (1250 to 1420 h) on a hot day [temperature-humidity index (THI) = 75.6; heat-load index (HLI) = 99.5; panel A] and a cool day (THI = 68.5, HLI = 67.3; panel B). The shaded bar refers to the 90-min treatment period. The pooled standard error of the difference was 0.05 ° C.
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The body temperature of control cows increased with higher values of THI and HLI (P 0.031; Figure 1). The effectiveness of the different cooling methods was dependent on ambient weather conditions. The hottest (THI = 75.6; HLI = 99.5) and coolest days (THI = 68.5; HLI = 67.3) in the experiment were selected to illustrate this effect (Figure 2). When a sprinkler was applied, also providing shade had little impact on the relationship between THI or HLI and body temperature.
When THI and HLI fell to < 69 and 77, respectively, there was a transient increase in body temperature in cows in the sprinkler group and in the combination of shade and sprinkler treatment group during the 90-min treatment period (Figures 1 and 2). For example, when the HLI was < 77, body temperature was higher in cows treated with sprinklers than in cows in the shade or control treatments (control: 38.5 ° C; shade: 38.4 ° C; sprinklers: 38.6 ° C; sprinklers and shade: 38.6 ± 0.06 ° C; P = 0.002), but when HLI was 77, cows in the control treatment had the highest body temperature (control: 39.2 ° C; shade: 38.7 ° C; sprinklers: 38.7 ° C; sprinklers and shade: 38.6 ± 0.11 ° C; P = 0.006).
Behavior
There were half as many tail flicks and hoof stamps when cows were treated with sprinklers compared with the control and shade treatments (Table 2). Cows exposed to sprinklers tended to spend more time with their heads in the low position and less time in the middle position compared with cows in the shade and control treatments (P = 0.096 and P = 0.038, respectively). Coat color influenced how the head position changed in response to some treatments (interaction between coat color category and shade, P = 0.016). Black cows were more likely to hold their heads in the middle position when in the shade (63 vs. 57 ± 5.6% in the shade and control treatment, respectively) compared with cows having a mix of black and white hair (60 vs. 63 ± 5.6% in the shade and control treatment, respectively). Temperature-humidity index and HLI did not influence the effect of treatment on head position, tail flicks, or hoof stamps.
Milk Production
Milk production declined from 16.1 to 11.2 kg/d over the duration of the experiment. Daily and a.m. milk production and milk composition did not differ among treatments (Table 4) or with coat color (black: 13.5 vs. mixed: 13.6 ± 0.28 kg/d). Somatic cell counts were lower in cows provided with shade alone. Daily milk production declined significantly with increasing HLI (P 0.017; Figure 3) for all but the shade treatment (P = 0.144). There was no relationship between milk production and THI (P 0.282).
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Figure 3. Daily milk production (kg/d, corrected for decline over the course of the experiment) in response to the heat-load index (HLI) over the 34 d of the experiment. Values are averaged across treatments; symbols represent daily values, and lines represent fitted regression curves.
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DISCUSSION
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This study demonstrated that the use of shade and sprinklers in the 90 min before the p.m. milking provided effective, immediate physiological relief to pasture-based dairy cows in the summer. Sprinklers and shade reduced respiration rates by 60 and 30%, respectively, compared with control cows. Other studies have reported similar relative reductions in respiration rate in dairy cows in response to these methods, particularly with water (Tarazón-Herrera et al., 1999). The combination of shade and sprinklers was the most effective at lowering the respiration rate. Cooling with a combination of water and shade also resulted in a lower respiration rate than with sprinklers alone in beef cattle (Mitlöhner et al., 2001), although the respiration rates in our study were lower than those reported by Mitlöhner et al. (2001), possibly because the weather in our experiment was cooler. Indeed, respiration rate increased on days with a higher THI and HLI, particularly for cows in the control and shaded treatments. Others found that shade reduced the respiration rate of dairy cattle with temperatures > 25 ° C, but not with temperatures below this level (Muller et al., 1994). In contrast, we found that respiration rates were consistently lower in cows under shade compared with cows in the control treatment across a range of ambient temperatures.
Shade quickly reduced body temperature by 0.3 ° C compared with control cows during the 90-min treatment period. This reduction in body temperature is similar to that reported by Muller et al. (1994) at the same time of day, particularly when the ambient temperature exceeded 25 ° C. In contrast, the drop in body temperature of cows under sprinklers was delayed compared with those under shade alone. Sprinklers provided a greater overall decrease in body temperature relative to the control or shade treatments. For example, the mean body temperature of cows under sprinklers was 0.2 ° C lower than that of control cows during the 90-min treatment period in our experiment but, in agreement with Araki et al. (1985), was still 0.5 ° C lower than control cows 4 h after cessation of the sprinkler treatment. Based on the results of Flamenbaum et al. (1986) and our own observations, it appears that once the sprinklers have stopped, it takes approximately 30 min before the minimum body temperature is reached in the afternoon. Cows under sprinklers had a body temperature 0.2 ° C lower than cows under shade alone 2 to 4 h after the 90-min treatment period, which is consistent with the report of Tarazón-Herrera et al. (1999) that cows exposed to evaporative cooling had lower body temperatures than shaded cows. Although the combination of shade and sprinklers was no more effective in decreasing body temperature during the 90-min treatment period than sprinklers alone, this cooling strategy provided both an almost immediate benefit from shade as well as longer term cooling from sprinklers. Indeed, relative to the control cows, body temperature remained 0.5 to 0.6 ° C lower in cows that were wet by sprinklers for 2 to 4 h after the treatment period and remained at least 0.2 ° C lower 6 h later, presumably because of residual effects of evaporative cooling. In comparison, the body temperature of cows in the control treatment continued to increase in the late afternoon before reaching a peak at 1610 h.
The effectiveness of the different cooling treatments in reducing the respiration rate and body temperature was dependent on ambient climatic conditions. On days when THI was 69 (HLI 77), the decreases in respiration rate and body temperature were most noticeable in cows under sprinklers (alone or in combination with shade) compared with cows in the shade alone and control treatments (Figure 2). For example, on the warmest day of the experiment (THI and HLI were 75.6 and 99.5, respectively), the maximum respiration rate and body temperature exceeded 110 breaths/min and 41 ° C, respectively, in many cows in the control treatment but remained below 40 breaths/min and 40 ° C in most cows under sprinklers. Conversely, when the daily mean THI was 69 (HLI 77), sprinklers caused a transient increase in body temperature in comparison with control cows, despite a reduction in their respiration rate. In an earlier experiment, exposure to sprinklers in the morning caused a similar increase in body temperature that ended when the sprinklers stopped (Araki et al., 1985). Clearly, the effectiveness and need for evaporative cooling were diminished at lower ambient temperatures. On cooler days, cows under shade had lower respiration rates than control cows; however, body temperatures did not differ between the shade and control treatments, indicating that the higher respiration rates were an effective cooling strategy. Indeed, the respiration rates of control cows on cooler days were within the normal range for cattle (Spiers et al., 2004). Once THI rose to 69, the body temperature of cows in the control group was higher than that of shaded cows, indicating that increases in respiration rates were no longer completely effective at regulating body temperature. Collectively, these results indicate that both shade and sprinklers are beneficial to cows by reducing their body temperature on hot, humid days when THI is 69 (HLI is 77).
Despite marked reductions in body temperature and respiration rate, the use of shade and sprinklers to cool cows before the p.m. milking affected neither daily nor a.m. milk production, nor milk composition. This is in direct contrast to the findings of Valtorta and Gallardo (2004), who reported an increase in both daily milk yield and the percentage of milk fat and protein in Holstein cows in response to evaporative cooling for at least 20 min before the a.m. and p.m. milkings. This discrepancy is likely a result of the lower ambient temperature in our study, which may also explain the relatively weak or nonexistent relationship between HLI or THI and milk production. It is possible that our sample size was insufficient to detect such differences. More recently, Bryant (2006) analyzed nearly 66,000 first-lactation records in New Zealand dairy cows over a 14-yr period in relation to weather conditions and reported a consistent reduction in milk yield per unit of THI above 67. Not only is this THI threshold lower than the much-published level of 72 (e.g., Igono et al., 1992), but it is also similar to the THI at which we first observed physiological responses. Together, these data provide evidence that relief from warm weather is likely beneficial at lower ambient temperatures than previously thought.
The use of sprinklers reduced the frequency of both tail flicking and hoof stamping. Previous work demonstrated that both these behaviors were positively associated with insect-avoidance and fly numbers (Eicher et al., 2001), and it seems likely that sprinklers reduce insect landings. In addition to the cooling benefits, reduced irritation from flies may be a reason to use sprinklers in the holding pen before milking.
Cows exposed to sprinklers spent more time with their heads in the low position and less time in the middle position compared with cows in the shade and control groups. This response was similar to the change in standing position in winter when, on colder and windier days, cows spend more time with their heads down (Tucker et al., 2007). In both situations, a lower head position may reduce the exposure of the head to water. Although sprinklers may provide benefits in terms of cooling and a reduction in fly-avoidance behaviors, changes in head position indicate that cattle may find sprinkling aversive. Head position did not change in response to weather conditions in the current experiment, and this may indicate that cows find sprinklers less aversive than rain in winter. Aversion was not measured directly, and only limited conclusions can be drawn from head position alone. Indeed, when given the choice, cattle will stand under sprinklers (Seath and Miller, 1948), and Miller et al. (1951) reported that the time spent under sprinklers increased with increasing air temperature, although no information was given about how other weather variables influenced sprinkler use or which part of the body cows chose to expose to water. Additional work is needed to understand the preferences of dairy cows for sprinklers and shade, and the effect of different climatic variables on these choices.
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CONCLUSIONS
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Shade reduced both the respiration rate and body temperature of cows before the p.m. milking. Sprinklers provided relief from insects and reduced the respiration rate more markedly than shade alone and cooled cows for several hours after milking. The reduction in body temperature and respiration rate attributable to shade and sprinklers was greatest on days when THI was 69 and the HLI was 77. Our results suggest that shade and sprinklers can be used at the milking parlor to improve the comfort and welfare of cows in a pasture-based system during hot weather.
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ACKNOWLEDGEMENTS
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The authors gratefully acknowledge technical assistance from the AgResearch staff: Kaye Bremner, Jennie Burke, Katie Carnie, Gonzalo Carracelas, Daniel Cullen, Debbie Davison, Suzanne Dowling, Frankie Huddart, Estelle Liedemann, Andrea Rogers, Haylie Stevens, and Kate Tappenden. We are grateful to the staff at Dexcel’s Scott Farm, and to Stuart Eaton and Max Behl for their building expertise. We thank Catherine Cameron, Vanessa Cave, and Neil Cox of AgResearch for help with the statistical analysis. This work would not have been possible without funding from Dairy InSight (Wellington, New Zealand) and the Foundation for Research, Science and Technology (Wellington, New Zealand).
Received for publication November 16, 2006.
Accepted for publication April 9, 2007.
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ABSTRACT
INTRODUCTION
), shade (
), sprinklers (
), or a combination of shade and sprinklers (+).