Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Other
Publication Acceptance Date: 10/8/2002
Publication Date: 3/20/2003
Interpretive Summary: A study was conducted to determine the response of cattle to normal and hot environments. It was determined that body temperature, breathing rate, and metabolic rate were affected by air temperature. Maximum breathing rate occurred about 2 h after maximum air temperature, while maximum body temperatures did not occur until about 4 h after maximum air temperature. Neither body temperature nor breathing rate pattern changed over the 11-day period. Metabolic rate decreased over the 11-day exposure to hot temperatures. There were no close relationships between body temperature, breathing rate, nor metabolic rate.
Technical Abstract: Heat stress in feedlot cattle causes reduced performance and in the most severe cases death, thus resulting in the loss of millions of dollars in revenue to the cattle industry. A study was designed to investigate the thermoregulatory responses of feeder cattle to both acute and chronic exposures to elevated temperatures. Nine beef steers, weighing 330 ± 8.2 kg, were randomly assigned to individual pens in one of three environmental chambers. Each chamber was subjected to each of three sinusoidal temperature treatments for a period of 11 days (temperature: 18±7, 30±7, 34±7º C and dew point: 7, 14, and 14º C, respectively) according to a Latin square treatment design with a 10-day thermoneutral period separating treatment periods (sinusoidal at 18±7). Heat production (HP), respiration rate (RR), and rectal temperature (RT) were measured on each animal for two 22-hour periods, one during the acute phase of heat stress (day two, three, or four) and the other during the chronic phase of heat stress (day nine, ten or eleven). Rectal temperatures and RR showed significant differences between treatments. Both RT and RR had a diurnal pattern, which followed the diurnal pattern of the ambient conditions; RT lagged ambient conditions by approximately 4.5 h while RR lagged ambient conditions by approximately 2 h. Heat production at thermoneutral conditions was significantly higher than at the heat stress treatments, and there was no difference in HP between the two levels of heat production. Heat production and respiratory quotient were the only two parameters shown to change with acclimation to heat stress.