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Title: ANALYSES OF THERMOREGULATORY RESPONSES OF FEEDER CATTLE EXPOSED TO SIMULATED HEAT WAVES

Author
item Brown-Brandl, Tami
item Eigenberg, Roger
item Hahn, George
item Nienaber, John
item MADER, TERRY - UNIVERSITY NEBRASKA
item SPIERS, DONALD - UNIVERSITY MISSOURI
item PARKHURST, ANNE - UNIVERSITY NEBRASKA

Submitted to: International Journal of Biometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2004
Publication Date: 5/1/2005
Citation: Brown Brandl, T.M., Eigenberg, R.A., Hahn, G.L., Nienaber, J.A., Mader, T.L., Spiers, D.E., Parkhurst, A.M. 2005. Analyses of thermoregulatory responses of feeder cattle exposed to simulated heat waves. International Journal of Biometeorology 49:285-296.

Interpretive Summary: Heat stress reduces performance and, in the most severe cases, causes death of feedlot cattle resulting in major economic losses. A study was designed to evaluate feed intake, feeding behavior, breathing rate, body temperature, and heat production of feedlot cattle under hot conditions. Nine feedlot steers were exposed to three different hot environments of varying patterns. Differences between environments were found and were dependant on the parameters used. Overall, it was found that parameters of breathing rate and feed intake gave an accurate assessment of the animal's well being as it relates to heat.

Technical Abstract: Heat stress in feedlot cattle causes reduced performance, and in the most severe cases, death of the animals, thus causing the loss of millions of dollars in revenue to the cattle industry. A study was designed to evaluate the dynamics of thermoregulation and feeding activities when feeder cattle were exposed to simulated heat waves in comparison with repeated sinusoidal hot and thermoneutral environments. Nine beef steers were randomly assigned to an individual pen in one of three environmental chambers. Each chamber was subjected to each of three temperature regimes (Heatwave simulation from Rockport, MO 1995, Heatwave simulation from Columbia, MO 1999, and Controlled heat stress treatment of 32 +/- 7 deg C) for a period of 18 days, according to a Latin square treatment design, with a 10-day thermoneutral period (18 +/- 7 deg C) separating treatment periods. Respiration rate, core body temperature, heat production, feed intake, and feeding behavior were measured on each animal for the duration of the experiment. Differences were found in all treatments for all parameters except feeding behavior. The severity of the stress was dependent on the response variable of interest. The response of respiration rate to temperature was found to be similar in all animals and have little acclimation effect. Therefore, overall recommendation is that respiration rate was found to be the overall best indicator of stress in a group of animals.