C. N. Lee

PHYSIOLOGICAL RESPONSES OF DAIRY COWS DURING EXTENDED SOLAR EXPOSURE

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.

THERMOREGULATORY RESPONSES ASSOCIATED WITH LYING AND STANDING IN HEAT-STRESSED DAIRY COWS

The purpose of this study is to characterize the thermoregulatory responses of unrestrained heat-stressed dairy cows within a freestall environment using fan and spray configurations for cooling cows while lying or standing. An experimental treatment sprayed individual cows lying in freestalls from 11:00 to 15:00 (stall cooling period) during hot-humid weather (average THI of 82.4) over a five-day trial period, using ultrasound transceivers to detect their presence. Core body temperatures were continuously monitored with vaginal temperature loggers. To assess behavioral responses, cows were visually monitored during the stall cooling period. Respiration rates and dorsal surface temperatures were recorded when the cow lay down or stood up in a stall. Core body temperature of lying cows rises at a rate of 0.6°C h-1 when exposed to fan cooling alone. Adding spray cooling to fan cooling slows the rate of rise to 0.3°C h-1. With or without freestall spray cooling, cows stand and seek cooling when their core body temperatures reach 38.9°C. Core body temperature is a more reliable indicator than either dorsal skin temperatures or respiration rates for predicting when cows stand and seek cooling. Core body temperatures of cows fall at a rate of 0.7°C h-1 while standing under feed line spray and fan cooling, while core body temperatures of cows standing under fans without spray remain unchanged. To cool heat-stressed cows, water spray is required in addition to fans while the cows are standing. Fans alone are inadequate.

Continuous Measurements of Vaginal Temperature of Female Cattle Using A Data Logger Encased in a Plastic Anchor

Vaginal temperatures of 20 pregnant dairy cows were continuously recorded using data loggers with built in temperature sensors for 3 weeks. Plastic anchors were designed and produced to hold data loggers inside the vagina of cows. The anchors were manufactured from plastisol - a flexible translucent plastic that could be molded to a desired configuration. The material is contact compatible with dairy products but is not known if it qualifies for a long-term implant. The plastic cures by heating to 160°C, which takes about one hour in an oven at a temperature of 215°C. The volume of material necessary to produce one anchor is about 90 cc. The system and procedure was reliable, accurate, low cost, easy to implant and does not fall out, and had no ill effects to the health of the cows or disturb their behavior/activities. Rectal temperatures were recorded using a high performance digital thermometer. The vaginal temperatures were compared to the rectal temperatures and the results matched to within 0.06 ± 0.015°C.

SWEATING RATE OF DAIRY COWS UNDER SHADE AND SUNNY ENVIRONMENTS

Sweating rates from live Holstein cows were measured using a closed chamber VapoMeter, and a portable calorimeter. Measurements were made when cows were in shade and exposed to direct sunlight under different air velocities. The effect of color of hair coat on sweating rate was compared. Comparisons of different sweat rate measuring systems were also compared. The sweating rate at zero air velocity using the VapoMeter was 62 g/h-m , and the sweating rates at 0.2 and 1.0 m/s measured using the portable calorimeter were 238 g/h-m and 333 g/h-m , respectively when ambient temperature was 33°C, relative humidity was 52% and solar load was 740 W/m .

Body Temperature and Behavioral Activities of Four Breeds of Heifers in Shade and Full Sun

Four breeds of heifers, eight of each breed, were housed in two types of feedlot pens – one with shade and the other with no shade (exposed to full sun). The breeds were: Black Angus, white Charolais, tan-colored MARC I, and dark-red colored MARC III. The objectives were to determine whether shade made a significant difference in thermal responses (animal activities and vaginal temperature) and to determine the effect of hair-coat color on body temperature due to solar exposure. Providing shade alleviated heat stress by lowering body temperature especially for black Angus and dark-red colored MARC III because of their higher hair-coat color capacity to absorb solar load. These two breeds spent more time standing in shade than the tan-colored MARC I and the white Charolais. The rate of increase of body temperature was higher when the heifers were lying down in full sun (0.61+0.27°C/h) followed by lying down in shade (0.25+0.17°C/h) because of reduced effective surface area to convective evaporative cooling (p<0.05). There was direct linear correlation (R2 ˜ 0.90) between solar absorbing capacity of hair coat and percent of time the heifers spent in shade. The percent of time spent in shade both standing and lying down for each breed was: 89% for Black Angus, 81% for dark-red MARC III, 57% for tan-colored MARC I, and 55% for white Charolais. The study suggested that shade was critical for feedlot cows, especially those with dark hair coat, allowing them to thermally regulate their physiologic needs.

Evaluation of Thermal Stress Indices for Cattle

Thermal environment is an important factor that affects the growth and development of domestic animals. Incorporating various environmental factors into an index greatly facilitates assessing and managing the environment for livestock. Thermal stress is reflected by the physiological responses exhibited by animals including skin temperature, core (rectal) temperature, sweating and respiration rates. In this study, the measurement data that consist of the physiological responses (skin temperature, rectal temperature, sweating rate and respiration rate) of cattle and environmental conditions (air temperature, relative humidity, solar radiation and air velocity)measured at four different sites cross US with different breeds of cows and heifers. The data were used to examine the probability distributions of the physiological responses-skin temperature, sweating rate and respiration rate of cows under stress conditions. Skin temperature and respiration rate were found to follow normal distribution and sweating rate follow Weibull distribution. The effectiveness of eight environmental indices (THI: temperature humidity index; THIadj: adjusted temperature humidity index; TBG: temperature of black globe; BGHI: black-globe humidity index; ETI: equivalent temperature index; ESI: environmental stress index; HLI: heat load index; RRP: respiratory rate predictor) were evaluated based on their correlation coefficients with the physiological responses. Skin temperature is the physiological response that responded to environment conditions sensitively. Among the eight thermal indices examined, THIadj, BGHI and RRP were those most correlated with skin temperature.

Sweating rates of dairy and feedlot cows under stressful thermal environments.

Sweating rates from heat-stressed dairy and feedlot cows were measured using a Portable Calorimeter and a Bovine Evaporation Meter. 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 and feedlot cows, and determine the level of influence of environmental factors (air temperature, relative humidity, solar load , 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). The range of sweating rates was between 189 ± 84.6 and 522 ± 127.7 g/m2-h, and that of body temperature was between 39.3 ± 0.53 and 41.7 ± 0.19 °C. Breed difference, hair-coat color. Solar load, and air velocity are critical (statistically significant at P-values <0.05) on sweating rates.

Cooling cows: the udder way

The objective of this study was to explore an alternative way to cool cows in time of heat stress. The procedure followed was to compare wetting the udder only to wetting the whole body. Twelve pregnant lactating Holstein cows were used in the study. The cows were exposed to four treatments each day over 4 days. The treatments were: (1) wetting the whole body without blowing air (n = 24), (2) wetting the whole body and blowing air (n = 12), (3) wetting the udder only without blowing air (n = 24), and (4) wetting the udder and blowing air directly towards the udder (n = 12). Water was sprayed until it dripped from the cow body. Identical fans were used to blow air onto the wet area, and were on until measurements of rectal temperature, respiration rate, and skin surface temperature both at the udder and body (chest to rear rib area) were taken. Respiration rates and skin temperatures were significantly higher (p> 0.05) when wetting the udder versus wetting the whole body. There was no statistical difference in rectal temperature between udder and whole-body wetting with or without air blowing onto the skin. Since rectal temperature is a measure of internal body temperature, it can be concluded that udder wetting alone is as effective as wetting the whole body in abating thermal stress of dairy cows. Blowing air onto the wet udder further decreased udder surface temperature. The rectal and vaginal temperatures were highly correlated (R = 0.93).

Alternative Cooling of Dairy Cows by udder Wetting

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 commonly practice, wetting the body. Twelve pregnant, lactating Holstein cows were used in the study. The cows were exposed to four treatments each day over 4 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 onto 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 temperature. There was a strong correlation (R=0.93) 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, removed the instantaneous and static measure of rectal temperature, could be considered as an accurate and reliable measure of body temperature of healthy dairy cows.

Physiological Responses of Dairy Cows during Extended Solar Exposure

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 react to a prolonged solar exposure, and (4) to compare dairy cows physiological responses to hot and humid versus hot and dry environmental conditions. The cows were divided into two groups of 6 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 was initially set at 83 and later at 79.6, and air velocity in the measurement area on the dorsal surface was between 0.8 and 1.2 m/s. Skin temperature was greater than 35°C (threshold for heat stress). There was considerable variation in sweating rates between cows of the Holstein breed. 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 and feedlot heifers is around 660 g/m2-h. A prolonged exposure to hot and dry environmental condition made entirely black or predominantly black cows to foam in the mouth, stick their tongues out, and drool, and immediate intervention with water spraying helped to alleviate the thermal stress.