|Carroll, Jeffery - Jeff Carroll|
|Chase, Chadwick - Chad|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2007
Publication Date: N/A
Technical Abstract: Two Bos taurus breeds with known differences in heat tolerance were tested under controlled conditions to establish distinctive heat tolerance characteristics. Romosinuano (RO) is a tropically adapted, Criollo breed recognized for its heat tolerance. Nine Angus (304 ± 7 Kg BW; AG) and nine RO (285 ± 7.5 Kg BW) steers, raised at USDA-ARS, Brooksville, Florida under identical conditions, were transported to the University of Missouri Brody Environmental Center. Steers were housed for 14 d at thermoneutrality (21 deg C; TN) before 14 d of cyclic heat stress (HS; 26 deg C night; 36 deg C day). Rectal temperature and respiration rate were measured six times daily. Sweat rates at shaved sites were recorded on specific days. Blood samples were taken once a week. The RO maintained a lower respiration rate (~20 BPM; P < 0.001), sweat rate (+6 g/m2/h; P < 0.0001), and rectal temperature (-0.5 deg C; P < 0.03) than AG throughout TN. Both breeds increased sweat rate, respiration rate, and rectal temperature during HS, with AG retaining the higher levels (P < 0.001). Many of the blood analyses, including electrolytes, glucose, and globulin, showed no effect of breed or HS. However, serum prolactin, leptin, creatinine, and cholesterol concentrations were generally higher in AG than RO, even at TN (P < 0.01). Angus demonstrated HS-induced increases in prolactin, leptin, creatinine, and cholesterol. However, RO displayed no increase in these parameters with HS. Serum prolactin typically increases with air temperature, and is traditionally used as a marker of heat strain. The present study has identified additional physiological and endocrine markers that may aide in the identification of Bos taurus sensitivity to heat. The reasons for these changes during heat stress remain to be determined.