PSIII-A-2 - Administering Anti-inflammatory Dexamethasone or Fish Oil Mitigated Components of the Inflammatory Response to Chronic Heat Stress and Improved Average Daily Gain in Whether Lambs

Abstract: Heat-stressed livestock exhibit systemic inflammation, which likely contributes to poor growth and metabolism even when nutritional effects are controlled by pair feeding. Thus, heat stress-induced deficits in growth, metabolism, and well-being may be improved by moderating heightened inflammation. Our objective was to determine whether targeting inflammation by administering anti-inflammatory dexamethasone or fish oil would mitigate blood indicators of inflammation and improve average daily gain (ADG) in heat-stressed lambs. Wether lambs were randomly assigned to 30d of heat stress (40°C, THI=88) or thermoneutral (pair-fed controls; 25°C, THI=70; n=11) conditions. Heat-stressed lambs were randomly assigned to receive no intervention (HS; n=11), oral boluses of fish oil (HS+FO; 360mg; n=11) twice daily, or IM injection of dexamethasone (HS+DEX; 0.15mg/kg; n=11) every 72h. Throughout the study, rectal temperatures and respiration rates were greater (P < 0.05) for HS, HS+DEX, and HS+FO than for controls. Plasma TNFα was greater (P < 0.05) for HS lambs (528±31pg/ml) than for controls (341±28pg/ml), HS+DEX (423±39pg/ml), or HS+FO lambs (376±38pg/ml). Total white blood cells and monocytes were greater (P < 0.05) for HS, HS+DEX, and HS+FO lambs than for controls. Granulocytes and granulocyte:lymphocyte were greater (P < 0.05) for HS and HS+DEX but not HS+FO than for controls. Lymphocytes did not differ among groups and platelets were less (P < 0.05) for HS+FO than for other groups. Blood pH was greater (P < 0.05) for HS, HS+DEX, and HS+FO than for controls early in the study but did not differ by d 30. Blood HCO₃ was less (P < 0.05) for HS but not HS+DEX or HS+FO lambs than for controls throughout the study. ADG was reduced (P < 0.05) by 22% for HS lambs but not for HS+DEX or HS+FO lambs compared to controls. These data indicate that supplementing anti-inflammatory agents to chronically heat-stressed lambs improved growth by reducing components of the inflammatory response.