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Title:   Author  item
                                            SCHARF, B - UNIV OF MISSOURI COLUMBIAitem
                                            WAX, LAURA - UNIV OF MISSOURI COLUMBIAitem
                                            Carroll, Jeffery

                                                         - *Jeff Carroll*item
                                            Chase, Chadwick

                                                         - *Chad*item
                                            Coleman, Samuelitem
                                            KEISLER, DUANE - UNIV OF MISSOURI COLUMBIAitem
                                            SPIERS, DON - UNIV OF MISSOURI COLUMBIA
  Submitted to: Journal of Animal Science
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 7/11/2007
                                    Publication  Date: 7/11/2007
                                    Citation: Scharf, B., Wax, L., Carroll, J.A., Chase, C.C., Coleman, S.W., Keisler, D., Spiers, D. 2007. Evaluation of physiological differences in heat tolerant (Romosinuano) and heat susceptible (Angus) Bos taurus cattle during controlled heat challenge [abstract]. Journal of Animal Science. 85(Suppl. 1):466-467.Interpretive Summary:
                                Technical Abstract: A study was performed to evaluate differences in thermoregulatory ability of two Bos taurus breeds with known differences in heat tolerance. Nine Angus (304 ± 7 Kg BW; AG) and nine Romosinuano steers (285 ± 7.5 Kg BW; RO) were housed in the Brody Environmental Center at the University of Missouri. Steers were housed for 14 d at thermoneutrality (Ta = 21 deg C; TN) before initiation of heat stress. Heat stress (HS) consisted of daily cyclic Ta (26 deg C night Ta:36 deg C day Ta) for 14 d. Steers were fed a typical feedlot diet at 1.6% of BW/d. Rectal temperature was measured with respiration rate six times daily. Sweat rates were recorded on specific days throughout the study on shaved shoulder and rump sites. Respiration rate at TN was higher (P < 0.001) in AG than RO, by approx 20 BPM. There was a breed x time interaction (P < 0.001) at TN with the AG slowly adapting over time, and no reduction in RO. Angus steers also maintained rectal temperature 0.5 deg C higher than RO at TN (P < 0.0001). Sweat rates were slightly different at TN (P < 0.04). Both breeds initially increased sweat rate more than 4-fold during HS, followed by reduction after 3 d. Higher sweat rate was maintained in AG even after HS adaptation period (P < 0.0001). Both breeds increased respiration rate during HS, with AG steers exhibiting the higher rate (P < 0.0001), followed by a slight increase after 7 d (P < 0.03). Rectal temperature increased during HS for both breeds (P < 0.003), but with a higher level in the AG breed (P < 0.001). Romosinuano steers exhibit a lower level of heat loss than Angus steers during heat stress, while maintaining a lower core temperature. This suggests that lower metabolic heat production between these breeds is a key determinant of heat tolerance.


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