J. Dairy Sci. 2009. 92:506-517. doi:10.3168/jds.2008-1012
© 2009 American Dairy Science Association ®
Effects of shade and sprinklers on performance, behavior, physiology, and the environment of heifers
N. M. Marcillac-Embertson1,
P. H. Robinson,
J. G. Fadel and
F. M. Mitloehner2
University of California, Davis, Department of Animal Science, One Shields Ave., Davis 95616-8521
2 Corresponding author: fmmitloehner{at}ucdavis.edu
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ABSTRACT
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The objective was to measure effects of cooling technique (shade vs. water sprinklers) on performance, behavior, physiology, and the environmental effect of 40 Holstein heifers housed in drylot corrals during the hot summer months. The experiment was a replicated crossover design with four 21-d periods and 2 treatments: 1) shades installed in the front half of the pen or 2) sprinklers, which applied water to the pen surface at 2-h intervals from 1100 to 1900 h. Animal performance measures were dry matter intake, average daily gain, and feed efficiency (gain:feed). Behavioral measures, elimination patterns, and corral spatial distribution were measured in 5-min scan frequencies over four 24-h periods. Physiological measures were rectal temperature, respiration rate, urinary urea N, and blood urea N. Environmental measures were corral soil surface temperature and moisture, particulate matter, and surface NH3 volatilization; meteorological measures were also collected. Shaded compared with sprinkled heifers had increased dry matter intake (3.4%), increased average daily gain (14%), and increased feed efficiency (11%). Heifers in shaded vs. sprinkler treatments had decreased respiration rates (13%). Behavioral differences between the treatments varied by time of day. Heifers spent most time in either the shaded or sprinkled areas of their corrals (65.9 and 64.2%, respectively). Elimination behavior occurred predominantly at the front of the corral in close proximity to the feed bunks and additionally at the water trough in sprinkled corrals. Sprinkler treatment had a 31.7% greater average corral surface moisture than the shaded treatment. Corral surface temperature varied based on areas of surface moisture, shade location, and elimination concentration within the corral. Sprinkled corrals had less particulate matter emissions than shaded (25%), but NH3 emissions were 46% greater in sprinkler vs. shaded treatment. Overall, the use of shade in heifer corrals improved heifer performance and physiological measures, but sprinkler treatment had less NH3 emissions from corral surfaces under heat stress conditions. Both cooling techniques affected spatial distribution and behaviors of the heifers, which affected pen usage and surface characteristics.
Key Words: dairy cattle • shade • sprinkler • environment
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INTRODUCTION
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Heat stress in cattle occurs when a combination of ambient environmental conditions cause the effective temperature of the environment to be above an animal’s thermoneutral zone (Armstrong, 1994). Ambient temperatures in California’s Central Valley often exceed the thermoneutral zone of dairy cattle in the summer, leading to heat stress conditions. In the summer of 2006, a catastrophic heat wave in the Central Valley lead to heat stress-related deaths in >20,000 dairy cows and sustained depressions in milk production. The effects of heat stress on dairy cattle have been well researched and include changes in performance (e.g., decreased DMI and ADG; West et al., 2003), physiology (e.g., increased respiration rate and body temperature; Muller and Botha, 1994b), and behavior (Mitlöhner et al., 2002). During hot and dry periods, cattle can affect air quality by increasing particulate matter (PM) emissions in the corrals via increased activity on dry pen surfaces. Heat increases the volatilization of NH3 from pen surfaces due to rapid hydrolysis of urea from urine, which leads to secondary particulate formation, known as PM2.5 (PM with an aerodynamic diameter of 2.5 µm or less).
Modifications of corral management (i.e., construction of shade or sprinklers, or both) can alter thermal load, behavior, and environmental effect of cattle. Various cooling techniques have been reviewed (Collier et al., 2006), but shade (Mitlöhner et al., 2001, 2002) and water application (Mitlöhner et al., 2001) successfully decreased the physiological effect of heat stress on cattle. Shade and sprinklers are used to affect corral utilization by cattle (Armstrong, 1994) by distributing manure throughout the pen. Broader manure distribution in turn can affect NH3 emission (Voorburg and Kroodsma, 1992) by decreasing the mixing potential of urine and feces, as well as PM production (Mitlöhner et al., 2002) by increasing soil surface moisture. Ammonia and PM emissions are of major concern, because animal feeding operations, such as dairies, can be major contributors of these atmospheric pollutants, affecting both human and animal health (Aneja et al., 2001).
The objective of the study was to determine the effects of cooling method (shade vs. sprinkler) on the performance, physiology, behavior, and environmental effect of Holstein heifers in drylot corrals during the hot summer months.
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MATERIALS AND METHODS
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General
The study was conducted at the Air Quality Research Facility, located at the University of California, Davis, during the months of July to October 2003. Forty Holstein heifers with an initial BW of 298 ± 3.0 kg were sorted by BW, and randomly divided into 4 groups, in which they remained for the entire study. Heifers were housed and treated in accordance with the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (FASS, 1999) and the Animal Care and Use protocol for the University of California, Davis. Heifers were fed a diet formulated to meet or exceed minimum NRC (2001) requirements consisting of alfalfa hay, oat hay, almond hulls, and a standard mineral mix (Table 1
) once daily at 0600 h. Feed amount was adjusted on a daily basis to allow for 10% refusals.
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Table 1. Ingredient and chemical composition of diets fed to heifers housed in drylot pens fitted with either shade or sprinklers
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Heifers were housed in 4 dirt-floored drylot corrals (Figure 1). Corrals were oriented west (front) to east (back) with a 10-m feed bunk along the front of the corral. The feed bunks were situated on a 1.3-m-wide cement feed apron. The remainder of the corral was dirt-floored with a 3% slope to allow for water runoff. A water trough with float-activated water supply was located along the south side of the corral and provided free access to water. Following recommendations (FASS, 1999), feed bunk space requirements of 0.6 m per heifer, 14 locking head gates per corral were installed along the 10-m feed bunk. The 4 corrals were separated from each other by 12.5-m-wide unoccupied dirt surface corrals.
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Figure 1. Schematic map for elimination behavior occurrence and sample locations for soil moisture samples, ground surface temperature, and NH3 measure. Corrals measured 10.4 x 21.3 m and had 8 sample locations. The 4 corrals only differed by either shade or sprinkler installations. Shade was only present for 2 shaded corrals, and sprinkler was only present for 2 sprinkled corrals. The top of the corral, adjacent to the feed apron, faces west, and the back of each corral faces east. Numbers in parentheses represent soil and NH3 sampling locations. Corral soil moisture samples were taken for sample locations 3 to 10. Ground surface temperature and NH3 measures were taken at locations 1 to 10.
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The 2 cooling treatments were 1) shade (no sprinklers) and 2) sprinklers (no shade). Each treatment was randomly placed in 2 of the 4 corrals during treatment periods.
Shade was provided in 2 of the treatment pens as a heat stress mitigation technique. The shades were constructed of solid tin sheets resting on 4.6-m-tall purlin construction (this height was sufficient to ensure a minimal amount of reflected solar radiation from the shades to the heifers; Collier et al., 2006). The shaded area was 65.0 m2, which allowed 6.5 m2 of shade per heifer. The north-to-south-oriented shades were positioned in the western part of the corral to maximize the amount of shade located in the corral during the day, and to aid in a more even distribution of manure over the corral surface by encouraging heifers to move with the shade throughout the day.
In the 2 sprinkled treatment corrals, water sprinklers were provided as a heat stress mitigation technique. The water sprinklers were installed at the water trough and had a 180° sprinkling pattern. The spray emanated 2.4 m above the corral surface and had a 9.7-m spray radius. A timer automatically activated the sprinkler for a period of 7 min, at 1100, 1300, 1500, 1700, and 1900 h, with sprinklers delivering water at a rate of 30 L/min. This application rate was chosen to maximize water application to the pen surface and keep it moist throughout the day without causing excessive water pooling on the pen surface, while also mimicking standard industry practices for California. Water droplets were large enough to penetrate the hair coat onto the skin, to maximize evaporative cooling effectiveness.
The study was conducted over four 21-d treatment periods, with each 21-d treatment period divided into a 14-d adaptation period followed by a 7-d sampling period. On d 21, heifers were weighed and moved to a holding pen. Corrals were scraped to remove manure build-up and were kept unoccupied for a 3-d period. To decrease pen effects, treatments, rather than heifers, were rotated through the corrals. Therefore, following a randomized schedule, shades and sprinklers were moved in each corral after each treatment period.
Performance
Feed rations were weighed daily at delivery, and feed refusals were collected, weighed, and dried to calculate DMI on a daily basis. Composite feed samples were collected weekly and stored at –20°C until they were pooled by 21-d period and analyzed by a commercial laboratory for DM, CP, OM, fat, P, Na, Cl, S, K, Ca, Mg, Cu, and Fe (Dairyland Laboratories Inc., Arcadia, WI). Determination of DM was by gravimetric loss of free water by heating to 105°C in a forced-air oven for 3 h according to the AOAC (1997) method 935.29. Crude protein was determined via combustion using the AOAC (1997) method 990.03. The P, Na, Cl, S, K, Ca, Mg, Cu, and Fe concentrations were determined following AOAC (1997, method 968.08) utilizing microwave digestion, acid filtration, and inductively coupled plasma atomic emission spectrometry.
Body weight measures were taken before feeding on d 1 and on d 21 of each treatment period using a single animal scale that was calibrated before each weigh period. The BW difference between the 2 weighing events was used to calculate ADG and feed efficiency (gain:feed).
Physiology
Four heifers per treatment pen (from the total of 10) were randomly chosen as focal animals for physiology sample collection. On d 15, focal animals in all 4 pens were sampled simultaneously at 1030 and 1700 h for all physiological measures. Respiration rate of the focal heifers was obtained before heifers were handled for sample collection by counting the flank movement (i.e., breaths) per minute. Heifers were restrained in automatic locking headgates at the feed bunks, and rectal temperature (Supervet livestock rectal thermometer, Syrvet Inc., Waukee, WI), blood, urine, and fecal samples were obtained.
Blood and urine constituents were sampled at 1030 and 1700 h based on their peak times of 4 h postfeeding and maximum ambient temperature, respectively. Blood samples were collected from coccygeal venipuncture into 10-mL sodium heparin Vacutainer tubes (Becton Dickinson and Co., Franklin Lakes, NJ), centrifuged at 5,000 x g for 10 min to obtain blood plasma, and stored at –80°C until further analysis. Blood samples were analyzed by wet chemistry methods for BUN with a Technicon Autoanalyzer (Pulse Instruments Ltd., Saskatoon, Saskatoon, Canada) using the diacetyl monoxime colormetric assay (Marsh et al., 1957).
Fresh urine samples were collected at 1030 and 1700 h through a cheesecloth filter and stored in an airtight container. Urine samples were frozen at –20°C within 2 h of collection and were stored until further analysis. Urine was later analyzed for urine urea N (UUN) as described for BUN.
Fecal samples were collected at 1030 and 1700 h by grab method directly from the heifer for N analysis. Fecal samples were stored at –20°C within 2 h of collection, then later dried, ground, and stored in airtight containers. Fecal samples were pooled by corral and analyzed in a commercial laboratory (J. L. Analytical Services, Modesto, CA) for OM, DM (AOAC, 1997; method 930.15), and CP (AOAC, 1997; method 990.03).
At the end of each 21-d treatment period, heifers were removed from corrals, and manure from each corral pen was scraped and transferred into a manure mixer wagon (Kirby, Merced, CA). A composite manure sample was collected from each corral pile, dried, ground, and stored in airtight containers within 2 h of collection. Manure samples were pooled by corral and analyzed by commercial laboratories for DM, OM, and CP (J. L. Analytical Services).
Behavior
Behavioral observations were conducted for 24 h on d 14 during each treatment period. Behavioral observations were conducted from a centrally located 4.57-m-high observation tower, which allowed for visual observation of all heifers. Observation started at 0400 h, using a 5-min scan sampling technique, which in previous studies (Mitlöhner et al., 2001) was correlated with a continuous behavior sampling technique. Behaviors recorded included defecation, urination, locomotion, feeding bouts, drinking, lying, standing, mounting, and agonistic behaviors as defined in Table 2. Observations were recorded for hourly spatial distribution of heifers, as well as urination and defecation frequency and location. To record spatial distribution and elimination events, the corral was divided into 8 sections (Figure 1
).
Environmental Measures
Meteorological Measures.
Climatic data were recorded daily using an automated weather station (Model 110-WS-16, Novalynx, Auburn, CA), which was centrally located at the east end of the corrals. Climatic measures included ambient temperature (°C), black globe temperature (°C; the effective temperature when ambient temperature, air movement, and solar radiation are integrated), relative humidity (%), and wind velocity (m/s). Measures were recorded in 15-min intervals. The temperature-humidity index, which is a measure of the degree of stress on dairy cattle, was calculated based on the ambient dry bulb temperature and relative humidity (Mader et al., 2002).
Soil Measures.
Ground surface temperature and soil moisture content of each corral was measured on d 20 of each treatment period. Locations for measurements were the same for each of the 4 treatment periods (Figure 1). Surface ground temperature was measured using a Raynger STPro infrared gun (Raytek Corp., Santa Cruz, CA) at 0800, 1200, 1400, and 1700 h.
Soil moisture was measured in each corral at 1000 h by inserting a 5-cm-diameter pipe 15 cm into the ground and coring a sample. Soil samples were placed in a plastic bag, immediately weighed, and dried in an oven at 105°C for 15 h, after which they were weighed to determine differential moisture content. Eight core soil samples were taken in each treatment pen (Figure 1). From these measurements, total corral moisture and moisture concentrations per sample location were determined and treatment moisture averages calculated.
Air Quality Measures.
Particulate matter with a median diameter size 
2.5 µm (PM2.5) and 10.0 µm (PM10) was measured using 4 DustTrak samplers (Model 8520, TSI Corporation, St. Paul, MN). Samplers were housed in environmental enclosures and mounted 2 m above in the center of the corrals for protection from the heifers. Measurements were conducted simultaneously in all treatments from d 14 to 21. Data were reported as 12-h averages.
Ammonia fluxes were measured simultaneously in all 4 treatment corrals on d 21, using isokinetic surface flux chambers (Odoflux, Odotech Inc., Montreal, Quebec, Canada) to estimate NH3 concentration. Ammonia flux was measured at the same locations as soil measures (Figure 1) based on Environmental Protection Agency (EPA) guidelines (Klenbusch, 1986) for surface emission measurements for area sources and chamber residence time (the time it takes for 1 complete air turnover cycle). Isokinetic flux chamber sampling methodology was developed according to recommendations from EPA and the California South Coast Air Quality Management District (Klenbusch, 1986; Howell, 1997), as well as from the flux chamber manufacturer (Odotech Inc.). An impinger sampling train containing 0.1 N H2SO4 was used to trap gaseous NH3 volatilized from the corral surface. Ammonium ions were analyzed in the acid solution using EPA method 300 ion chromatography (Dionex ICS90, Dionex Corp., Sunnyvale, CA) and then were converted to NH3 based on calculations from Howell (1997). Ammonia concentration data were reported for corral averages in milligrams per kilogram.
Experimental Design and Statistical Analysis
The experimental design was a replicated crossover design, with 2 treatments and four 21-d treatment periods. The treatment order equalized carryover effects. The variable of interest was treatment (dichotomous categorical variable); period and corral were controlled for in each model (categorical class variables). Behavioral data were averaged per hour, converted to percentage of total time per hour, and arcsine square root-transformed to achieve normal distribution (Mitlöhner et al., 2001). Behavioral data were then analyzed by time. Elimination data were analyzed both by location within corral and by time, separately. Ground surface temperature and soil moisture data were analyzed by total pen and by location within the corral. Spatial distribution data were analyzed by time and location within pen, as well as presented descriptively. All data were analyzed using PROC GLM procedures in SAS (SAS Institute, 1999) with a significance level of P < 0.05.
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RESULTS
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Performance
The ADG (Table 3) was 14% greater (P < 0.001) in shaded vs. sprinkler treatments. Dry matter intake was 3.4% greater (P = 0.03) in shaded vs. sprinkler treatments. Feed efficiency was improved 13% (P = 0.002) in shaded vs. sprinkler treatments.
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Table 3. Animal performance measures (ADG, DMI, feed efficiency) averaged over measurement periods for shaded and sprinkled heifers
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Physiology
Heifers in shaded vs. sprinkler corrals showed a 13% decrease (P = 0.002) in respiration rates, but rectal temperature, BUN, and UUN were not affected by treatment (Table 4). The total N in feces was not different between treatments (shade = 2.78% DM, sprinkler = 2.73% DM; P > 0.05). The percentage of N loss between fresh feces and scraped manure (collections were 3 wk apart) was not different between sprinkler (53%) and shaded pens (41%; P = 0.13).
Behavior
Behavioral results are presented by time and treatment (Figure 2) for standing, lying, locomotive, drinking, agonistic, mounting, and feeding behaviors. No differences were observed between treatments for agonistic, mounting, drinking, and locomotive behaviors. A time x treatment (shade vs. sprinkler) interaction was significant for lying (P < 0.05) and feeding (P < 0.05) behaviors. Lying behavior was greater (P < 0.05) in shaded corrals during the hours of 1000, 1100, 1400, and 1600 h (SEM = 1.2, 2.3, 1.9, and 2.1%, respectively); lying behavior was greater in sprinkled corrals during the hours of 1500 and 1700 h (SEM = 1.9 and 1.7%, respectively). Feeding behavior was greater in shaded versus sprinkled corrals during the hours of 1200, 1500, and 1700 h (SEM = 1.2, 1.4, and 1.4%, respectively) but lower during hours 1100 and 1600 h (SEM = 0.9 and 1.1%, respectively).
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Figure 2. Behaviors of heifers housed in either shaded (SH) or sprinkled (SP) corrals over time. Behaviors are reported as percentages of time of over a 24-h period. *Indicates P < 0.05 between treatments.
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Spatial distribution patterns (data not shown) indicate that heifers in shaded corrals spent a greater portion of the daylight hours under the shade versus the nonshaded area (65.9%; P = 0.02). Similarly, heifers spent more of the midday hours in the sprinkle radius versus the nonsprinkled part of the corrals (64.2%; P = 0.04).Yet, when the sprinklers were turned on, heifers in sprinkler treatments moved away from the sprinkle radius, usually toward the feed bunk.
In both treatments, elimination behavior patterns differed (P < 0.01) throughout the corral. Corrals were divided into 8 locations (Figure 1), with location 1 being at the front (west) of the corral near the feed apron and location 8 being the back (east) of the corral. Figure 3 shows the elimination (i.e., urination and defecation) behavior frequency by location within corral. In both treatments, the frequency of elimination behavior at the front of the corral at location 1 was 5.6 eliminations/h (P < 0.01), whereas the frequency at the back portion of the corral at locations 7 and 8 was 0.3 and 0.4 eliminations/h (P > 0.05). In sprinkled pens, location 6 (the area closest to the sprinkler) had 74% more elimination events than shaded pens (3.4 vs. 0.9 eliminations/h, respectively; P = 0.02). Figure 4 reports the times at which elimination behaviors occurred. In both treatments, the majority of elimination events coincided with the morning feeding time at 0600 h (adjusted mean = 17.5 eliminations/h; P < 0.001) and in the evening between 1600 and 1800 h (adjusted means = 11.5 and 11.0 eliminations/h, respectively; P = 0.07).
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Figure 3. Frequency (number/h) of elimination behaviors (urination and defecation combined) reported by treatment and location in shaded and sprinkled corrals. Location 1 represents the front (west) section of the corral, location 6 represents the area around the water trough, and location 11 represents the back (east) section of the corral. Corrals are represented by location 1 to 8. Effects of shade vs. sprinkling were analyzed by location. The pooled SEM = 0.37. Data were analyzed by location with * indicating P < 0.05 between treatments.
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Figure 4. Frequency (number/h) of elimination behaviors (urination and defecation combined) in heifers housed in either shaded or sprinkled corrals reported by treatment and time. The pooled SEM = 0.57.
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Environment
Meteorological Measures.
Average maximum ambient temperature exceeded 30°C, and average black globe temperature exceeded 37°C for each treatment period (Table 5). These values exceed the upper threshold limit of the thermal neutral zone of 27°C for cattle (Armstrong, 1994). The average relative humidity was approximately 22% during the daytime (0800 to 1900 h) and 78% (2000 to 0700 h) at night. The average wind velocity was between 1.24 and 1.58 ± 0.45 m/s for each measurement period. The daytime average maximum temperature-humidity index was 82.3 ± 5.4.
Soil Measures.
Soil moisture by location is presented in Figure 5, and total pen soil moisture data in Table 6. Sprinkled vs. shaded treatments had a 31.7% increase (SEM = 1.75; P = 0.001) in total corral moisture. A treatment x location interaction was observed (P = 0.003). Sprinkler treatments had the greatest (P > 0.05) moisture on the south side locations 3, 5, and 7 (27.4, 21.1, and 26.4%, respectively), whereas shaded treatments had the greatest moisture (P > 0.05) at the shaded area at locations 3 and 4 (23.8 and 22.4%). Areas with the lowest moisture concentrations were found in the shaded corrals at locations 8 and 10 (moisture concentration <5%).
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Figure 5. Corral soil moisture gradient for each treatment. Soil moisture was measured to a depth of 15 cm. Numbers are average values for treatments reported in percentages of moisture. Panel (a) depicts the shade (SH) corrals. Boxes outlined in bold represent the location of shade within the corral. Panel (b) shows the sprinkled (SP) corrals. Black circles represent sprinkler location, and dashed lines represent the sprinkle radius. Data were analyzed by location. The pooled location SEM = 1.75. *Indicates P < 0.05 between treatments within each location.
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Ground surface temperatures differed between treatments and locations (SEM = 1.6; P < 0.05). Surface treatment sampled at 1200 h (Figure 6) was 30.9% lower in shaded corrals at the shaded location 6 (P < 0.001) and 20.5% lower in sprinkled corrals at the sprinkled locations 7, 8, 9, and 10 (P < 0.001). Regardless of treatment, the middle area of the pen (locations 5 and 6) had a 13.8% lower ground surface temperature than the rest of the pen, as well as the west area of each treatment corral (locations 1 and 2) closest to the feed bunks, which was 12.8% lower than the rest of the pen. The southwest location was the area where heifers slept at night, as well as the area of greatest elimination behaviors (Figure 3) and increased soil moisture. Surface temperature was greatest at the northeast portion of the corral for all treatments (locations 8 and 10), where the shade did not reach, and elimination frequency and water application (i.e., at the periphery of the sprinkle radius) were the lowest. Overall, ground surface temperature was lowest in areas of shade or greatest moisture content.
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Figure 6. Corral ground surface temperature at 1200 h. Values are reported in °C. Panel (a) depicts the shade (SH) corrals. Boxes outlined in bold represent the location of shade within the corral. Panel (b) shows the sprinkled (SP) corrals. Black circles represent sprinkler location, and dashed lines represent the sprinkle radius. Data were analyzed by location within corral. The pooled SEM = 1.6. *Indicates P < 0.05 between treatments within location.
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Air Quality Measurements.
Twelve-hour PM10 concentrations were 25% lower (P = 0.015) in sprinkled vs. shaded treatments (Table 6). Twelve-hour PM2.5 concentrations were not different between treatments. For both treatments, PM2.5 and PM10 concentrations were greatest (0.067 and 0.303 µg/m3, respectively; P = 0.02) at 0600 h (i.e., feeding time), and in the evening between 1700 and 1900 h (0.115 and 0.214 µg/ m3, respectively; P = 0.04), the time of the greatest locomotive behavior of the heifers.
Ammonia emission measurements were collected from 0900 to 1800 h for each sample period to represent the average concentration over the day. Ammonia concentrations were 46% greater (P = 0.038) in sprinkled vs. shaded treatments (Table 6).
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DISCUSSION
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The present study reported on the effects of heat on performance in heifers that were housed in either shaded or sprinkled corrals. The literature largely discusses responses to heat stress of shaded vs. nonshaded cattle. For discussion purposes, heifers in the present study that were housed in sprinkled corrals have been placed in the nonshaded category. This is justified, because heifers housed in sprinkled corrals did not make direct use of the water for cooling purposes.
Although performance was high in both treatments, shaded versus sprinkled heifers maintained a greater level of performance (DMI, ADG, and greater gain:feed). These observations agreed with findings on the effects of shade on cattle performance by other investigators (Mitlöhner et al., 2002; West et al., 2003). Mader et al. (2002) concluded that feed intake was directly linked to an increase in metabolic heat production and that by restricting DMI in cattle, body core temperature was decreased. Muller and Botha (1994a) found that feed consumption during the hot portion of the day was lower for nonshaded vs. shaded cows, because nonshaded cows were not able to dissipate the heat associated with feed digestion. The present study confirmed these earlier findings and noted during behavioral observations that feed intake was decreased in sprinkled vs. shaded heifers during the hot portion of the day (i.e., 1200, 1500, and 1700 h). The response of heifers to summer heat was reflected in their physiology. Because respiration rate is an indicator of respiratory evaporative cooling, an increase indicates that the animal is actively dissipating excess heat. In the present study, respiration rate in sprinkled heifers was 15% greater than in shaded animals, indicating a greater rate of respiratory heat loss. This result indicates that sprinkled heifers were not experiencing desired evaporative cutaneous cooling loss, likely due to a lack of wetting of the skin by the sprinklers. The result is consistent with other studies that reported lower respiration rates in shaded vs. non-shaded heifers due to more efficient cooling mechanisms (i.e., conductive and convective heat loss; Muller and Botha, 1994b; Mitlöhner et al., 2002).
Contrary to what was expected, the present study found no difference in rectal temperature between morning and evening measurements, or between the treatments. Because no difference was found for rectal temperature between the shaded and sprinkled treatments, the effect was likely due to the combination of high relative humidity, high ambient temperatures, and low wind velocities, all of which effectively decrease an animal’s heat loss potential, thus increasing body temperature in both treatments (Berman, 2006). These finding are consistent with Muller and Botha (1994b), who reported an increase in rectal temperature between morning and evening, but no differences between shaded and nonshaded cows. The lack of treatment differences in UUN and BUN was likely due to the high variability in heifers between treatments. This high variability in UUN between heifers in similar treatment groups was noted by Petersen et al. (1998). Although the present study did not use an untreated control, other workers found that cows exposed to cooling treatments (shade and sprinklers) vs. the untreated control animals show an increase in milk production (West, 2003) and greater reproductive efficiency (Collier et al., 2006).
Behavioral measurements demonstrated that heat affected cattle behavior in sprinkled vs. shaded heifers. Mitlöhner et al. (2002) observed that shaded vs. nonshaded heifers had increased lying behavior. Shultz (1984) reported that cattle lying under shade dissipated heat to the cool ground via conduction, because the surface temperature under the shade was considerably cooler than any other part of the corral. The present study observed that heifers in shaded vs. nonshaded treatments exhibited more lying behavior and stayed under the shaded area of the corral during the hottest part of the day between 1200 and 1800 h. Because heifers spent the majority of the daylight hours under the shade, they concentrated their elimination behaviors in this area, which increased ground moisture and decreased surface temperature. For the same reason, heifers in sprinkler treatments crowded around the sprinkled area of the corral where moisture cooled the ground surface, increasing the potential for conductive heat loss from the heifer’s body to the ground. Carroll et al. (1974) found that although sprinkling decreased maximum daily corral ambient temperature by 5°C, it raised the relative humidity by 10%. Because the 2 traits, decrease in temperature and increase in relative humidity, are mutually compensating effects, it is suggested that sprinkling might have no effect on the evaporative cooling ability of cattle. Other studies investigating the lying and standing behaviors of shaded and nonshaded cattle report that nonshaded vs. shaded cattle displayed more standing behavior (Mitlöhner et al. 2002), which was not confirmed in the present study. In the present study, sprinkled heifers laid down in the outer range of the sprinkler radius where the moisture concentration was between 8 and 10%, rather than in the inner radius where moisture concentrations averaged between 20 and 26%.
The frequency of elimination (urination and defecation) events, as well as their location within a corral, was temporally structured (Aland et al., 2002) and dependent on the environment (White et al., 2001). Aland et al. (2002) noted that approximately 95% of animals defecated or urinated, or both, shortly after rising from longer resting periods, usually at 0500 h after nighttime resting. Additionally, Aland et al. (2002) found that during or after eating and drinking bouts, about 60% of animals defecated or urinated, or both. White et al. (2001) reported that the number of elimination events that occurred in a given location was highly correlated to the time spent there. The present study noted that most elimination behavior occurred between 0600 and 0800 h, the time period in which heifers arose from night resting and were fed, and subsequently between 1600 and 1800 h, the second major feeding period of the day. Heifers in all treatments concentrated their elimination behaviors at the front of the corral where they rested at night, and where the feed bunk was located. The high elimination frequency near the feed bunk led to high ground surface moisture concentration at this location. The moisture concentrations in the front of the corral averaged between 22 to 26% and were comparable to those in areas of greatest water deposition in sprinkled corrals (i.e., 26% moisture). Armstrong (1994) reported that heifers in shaded corrals increased their elimination behaviors under the shaded area of the corral, which was confirmed in the present study. Heifers in sprinkled corrals showed an increase of elimination behaviors around the water trough. This result is supported by White et al. (2001), who observed that dairy cows on pasture concentrated elimination behaviors around the water trough during the summer months.
The soil moisture of the corral was affected by elimination behavior and water application, both of which affected the ground surface temperature of the corrals. The areas of greatest surface temperature (i.e., the back portion of the corral) were the areas with the lowest moisture and lowest number of elimination events. The back portion of the corral was always unshaded, and heifers avoided this area until the evening. Over the course of the day, the areas of lowest surface temperature (i.e., the front portion of the corral) were not only the shaded and sprinkled areas in their respective treatment corrals but were the areas of greatest elimination behavior and moisture concentrations. The areas of lowest ground surface temperature were the areas where heifers rested and spent the majority of their time, suggesting that the deposition of excreta and subsequently the surface moisture concentration was affected by the management and layout of the corral (Armstrong, 1994; White et al., 2001).
The soil moisture and ground surface temperatures of the corrals had an influence on total PM concentrations. The addition of moisture to the corral surface decreased airborne PM by binding soil and manure particles together (Miller and Berry, 2005). To achieve optimal dust reduction, without increasing odor production, a surface moisture concentration of 28% has been recommended (Miller and Berry, 2005). In the present study, it was noted that the sprinkled versus shaded corrals had greater ground moisture concentration, suggesting that moisture was responsible for decreasing PM10 concentrations. Increased ground surface temperatures observed in shaded treatments likely led to an increase in moisture evaporation and disassociation of particles, thereby leading to a greater potential of PM emissions. Because animals spent the majority of their daytime in the front of the pens where surface moisture was greatest (15 to 26% moisture), daily PM concentrations were lowest during midday hours. Nonetheless, in the evening when cattle were more active and utilized the back portion of the pens (3 to 10% moisture), PM emissions increased.
Ammonia concentrations were greatest in sprinkled treatments, which might be explained by an increase of hydrolysis of urea N due to the introduction of water to manure on the corral surface. Because NH3 is highly soluble in water, it accumulates in solution in wet areas of the corral, thus increasing the volatilization potential of NH3 during evaporation (Muck, 1982; Miller and Berry, 2005). An increase in ambient temperature increased the rate of N volatilization from manure (Voorburg and Kroodsma, 1992; Bussink and Oenema, 1998), due to a shift from aqueous to gas phase constituents. Therefore, the volatilization potential for sprinkled versus shaded treatments was increased due to intermittent sprinkling from 1100 to 1900 h, when ambient temperatures and evaporation potential were greatest. Analysis of total N concentrations in fresh feces vs. 3-wk-old manure found that sprinkler versus shaded pens lost 23% more N from manure and 48% more N as NH3. Total manure N losses (fecal N - manure N), which included loss via NH3 volatilization, were between 41 and 53% for both treatments. This is in relative agreement with other corral studies, which have shown that about 60% of the total N in manure was lost as NH3 or N2O (Bussink and Oenema, 1998).
In sprinkled corrals, an increase in the frequency of elimination behaviors in the sprinkled area of the corral contributed to the increase in NH3 volatilization by increasing the concentration of urea and urease in solution (Muck, 1982). In shaded corrals, most elimination behaviors occurred at the front of the corral and under the shades.
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CONCLUSIONS
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Results of the present study indicate that corral pen management in the form of installation of shade and sprinklers can affect heat stress in cattle, but may lead to environmental effects. Shade had the greatest success in maintaining animal performance and physiology under heat stress conditions; animal behavior, spatial utilization, and elimination patterns affected all other measured variables; and water application to the soil surface may decrease dust (decrease of 24% in PM10) but may increase NH3 volatilization (86% increase). The conclusion that each treatment had both a positive and negative effect on many of the traits suggests that a combination of mitigation techniques might be necessary to decrease the effect of heat stress on drylot heifers.
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ACKNOWLEDGEMENTS
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This study was supported by the Merced County Department of Public Health and State Water Resources Control Board. We thank Eddie Veenendahl, Sergio Burgos, Lisa McDonald, Leticia Valadez, Kevin Eslinger, and Andrea Schnitz (Department of Animal Science, University of California, Davis) for their assistance with the experiment. Additionally, we thank USDA-ARS in Lubbock, Texas, for the use of the Dust-Traks.
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FOOTNOTES
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1 Present address: Whatcom Conservation District, 6975 Hannegan Road, Lynden, WA 98264. 
Received for publication January 11, 2008.
Accepted for publication September 25, 2008.
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ABSTRACT
INTRODUCTION
