Evaluation of Physiological and Blood Serum Differences in Heat Tolerant (Romosinuano) and Heat Susceptible (Angus) Bos Taurus Cattle for Determination of Markers of Sensitivity

Two Bos taurus breeds with known differences in heat tolerance were tested under controlled conditions to evaluate heat tolerance. Romosinuano (Romo) is a tropically adapted breed. Nine Angus (304 ± 7 Kg BW) and nine RO (285 ± 7.5 Kg BW) steers from USDA-ARS, Brooksville, Florida, were transported to the Brody Environmental Center at the University of Missouri. Steers were housed for 14 days at thermoneutrality (21°C; TN) before 14 days of cyclic heat stress (HS; 26°C night; 36°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 Romo maintained a significantly lower respiration rate (20 bpm), sweat rate (6 g/mh), and rectal temperature (0.5°C) than Angus throughout TN. Both breeds increased sweat rate, respiration rate, and rectal temperature during HS, with Angus retaining the higher levels. There were breed differences for serum prolactin, leptin, creatinine, and cholesterol, with Angus being higher than Romo. Serum leptin increased for both breeds with HS. Although there were no breed differences at TN, Angus steers exhibited HS-induced increases in prolactin, creatinine, and cholesterol. However, these measures for Romo were unaffected by HS. 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.