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The objective of this study was to evaluate the effect of pregnancy, breed, and hair coat on body temperature and sweating rate (SR) of hair sheep. St. Croix White (STX; n = 9) and Dorper x STX (DRPX; n = 9) ewes (3.6 yr of age) were evaluated over 4 d at 126 d of gestation (PREG) and over 4 d at 46 d postpartum (OPEN) in the shade and sun and in the morning (AM; 0900 to 1200 h) and afternoon (PM; 1300 to 1600 h) after a 20 min acclimation to each condition on each day. Data loggers recorded vaginal temperature (VT) at 10-min intervals for 96 h. Rectal temperature (RT) was measured using a digital veterinary thermometer, and respiration rate (RR) was measured as breaths per minute (bpm). Sweating rate was calculated from measured air properties passing over a shaved (300 cm²) and unshaved area of the ewes' body using a portable calorimeter. Data were analyzed using GLM procedures of SAS (SAS Inst. Inc., Cary, NC) with breed, pregnancy status, sun exposure, and time of day as main effects. Mean temperature, relative humidity, temperature-humidity index, wind speed, and solar radiation on the days of data collection were 28.2°C, 82.8%, 80.3, 4.2 km/h, and 237.5 W/m², respectively. There was no difference (P > 0.10) in RT, RR, and SR between DRPX and STX ewes. The PREG ewes had lower RT (P < 0.007) and SR (P < 0.0001) and higher RR (P < 0.007) than OPEN ewes (38.5 ± 0.2 vs. 39.1 ± 0.2°C, 70.2 ± 3.1 vs. 88.3 ± 3.1 g⋅m-2⋅h-1, and 79.5 ± 2.2 vs. 72.1 ± 2.2 bpm, respectively). During the PM, RR, RT (P < 0.05), and SR (P < 0.006) were higher than in the AM. In the sun, RR (P < 0.001) and SR (P < 0.0001) were higher than in the shade, but there was no difference (P > 0.10) in RT. There was no difference in SR (P > 0.10) between the shaved and unshaved area of the ewe. The DRPX ewes had higher (P < 0.0001) VT than STX ewes. The PREG ewes had higher (P < 0.001) VT than OPEN ewes during the night time and lower VT than the OPEN ewes during the day time (P < 0.0001). The OPEN ewes had a greater (P < 0.009) daily range of VT than PREG ewes did (2.5 ± 0.4 vs. 1.1 ± 0.4°C, respectively), but there was no breed difference (P > 0.10). Hair coat did not have an influence on the SR of the ewes, and PREG ewes appeared to use increased respiration as opposed to sweating to help control RT. The narrower range of body temperature, measured as VT, of PREG compared to OPEN ewes may be a protective mechanism for the developing fetus. [ABSTRACT FROM AUTHOR]

Heat stress is a major inhibitor of production in livestock operations, causing severe economic loss. The objective of this study was to explore an alternative way to cool cows in time of heat stress by wetting the udder, as opposed to the common practice of wetting the body. Twelve pregnant, lactating Holstein cows were used in the study. The cows were exposed to four treatments each day over four days. The treatments were: (1) wetting the body without blowing air (n = 24), (2) wetting the body and blowing air (n = 12), (3) wetting only the udder without blowing air (n = 24), and (4) wetting the udder and blowing air directly onto the udder (n = 12). Water was sprayed over both sides of a cow's back until it dripped Similarly, this was done for the udder wetting treatment. Fans were used to blow air onto the wet area and were turned on until measurements of rectal temperature, respiration rate, and skin surface temperature, both at the udder and body (dorsal), were taken. Respiration rates and skin temperatures were higher (p > 0.05) with udder wetting compared to body wetting. However, there was no statistical difference in rectal temperature between both wetting cases with or without blowing air on- to the wet surface. Since rectal temperature is a measure of internal body temperature, it can be concluded that udder wetting alone was as effective as body wetting in abating thermal stress of dairy cows. Blowing air onto the wet udder further lowered udder skin surface temperature. There was a strong correlation (R = 0.91) between vaginal and rectal temperatures. Vaginal temperature, which provides the ability to continuously record over a prolonged time by implanting a sensor in the vagina, could be considered as an accurate and reliable measure of body temperature of healthy dairy cows. [ABSTRACT FROM AUTHOR]

Sweating and respiration rates, and skin (dorsal) and core (rectal) temperatures of 12 Holstein dairy cows were measured in controlled environments at the William Parker Agricultural Research Complex, University of Arizona-Tucson. The focus of the study was: (1) to establish the pattern (linear or periodic) of sweating, (2) to establish whether skin or core temperature drives sweating, (3) to determine how cows respond to a prolonged solar exposure, and (4) to compare dairy cows physiological responses to hot and humid versus hot and dry environmental conditions. The 12 cows were divided into two groups of six cows each and were housed alternately between two chambers. The two chambers were identical, but one (experimental chamber) included solar lamps to simulate solar load. The cows were alternately exposed to 550 W/m² solar load, THI at 79.6, and air velocity in the measurement area (dorsal surface) was maintained at 1.0 m/s. Skin temperature was greater than 35 °C (threshold for heat stress). There was considerable variation in sweating rates between cows. Cows sweat in a cyclic manner, and the results suggest that skin temperature is the primary driving force for sweating. The maximum sweating rate of dairy cows was around 660 g/m²-h. [ABSTRACT FROM AUTHOR]

Sweating rates from heat-stressed dairy cows and beef heifers were measured using a "Portable Calorimeter" and a "Bovine Evaporation Meter" designed and fabricated for the studies reported herein. Measurements were taken when cows were in their natural habitat. The focus of the study was to compare sweating rates measured from different breeds of dairy cows and beef heifers, and determine the level of influence of environmental factors (air temperature, relative humidity, solar load, and air velocity) and hair-coat color on sweating rate. The cows were exposed to solar radiation greater than 500 W/m² (average 833 ±132 W/m²), average THI was 82.7 ± 1.64 for all studies except for the Nebraska data where the THI was 77.4 ± 4. Air velocity in the sample area was between 0.8 and 1.2 m/s, and body (rectal) temperature was greater than 38.8°C (threshold for heat stress). Sweating rates ranged between 189 ± 84.6 and 522 ± 127.7 g/m²-h. Body temperature ranged between 39.3 ± 0.53°C and 41.7 ± 0.19°C. Differences in sweating rates were statistically significant at P < 0.05 between breeds, between black and white hair coats, and changes in solar load, relative humidity, and air velocity. Wetting the skin surface and increasing air velocity profoundly increased evaporation rate by converting sensible heat to latent heat. [ABSTRACT FROM AUTHOR]