Effect of various doses of injected selenium on performance and physiological responses of sheep to heat load.

The aim of the study was to determine the effects of various doses of injected Se on the physiological responses of sheep to heat load. Fifteen 9-mo-old Australian Merino wethers (mean BW = 27.2 ± 2.1 kg) were randomly assigned to 1 of 3 treatments: 0 (control), 0.5, and 5 mg of Se, which was administered as a subcutaneous sodium selenate injection (5 mg/mL Se) on d 1, 8, and 15 of exposure to heat stress. The animals were housed individually in an environmental chamber and exposed to high temperature from 0700 to 1800 h (maximum = 38°C; minimum = 24°C) and to thermoneutral temperature from 1800 to 0700 h (maximum = 24°C; minimum = 20°C) for 21 d. Rectal temperature (RT) and respiration rate (RR) were measured daily at 0800, 1200, and 1600 h. Feed intake was measured daily, and sheep were weighed on d 1, 8, 15, and 21. Blood samples were collected on d 1 and 21. The 5 mg Se treatment decreased RT by 0.3°C (P = 0.02) and BW loss by 4.5% (P < 0.05) and increased eosinophil count (P < 0.05). There were no differences (P > 0.05) between treatments in RR and DMI, serum concentrations of glucose, total protein, cholesterol, and NEFA or in blood hematology variables. The findings of this study have important implications for the sheep industry. Further studies are warranted to elucidate the dynamics of Se on productivity and health during hot conditions.