The effects of endophyte-infected tall fescue consumption and use of a dopamine antagonist on intake, digestibility, body temperature, and blood constitutents in sheep

Two experiments were conducted with lambs that consumed endophyte-infected (Acremonium coenophialum) tall fescue diets under elevated temperature and humidity and supplemented with the dopamine antagonist metoclopramide (M). In Exp. 1, 12 ruminally cannulated wethers (average weight 49 kg) were allotted by weight to either an endophyte-free diet (E-) or endophyte-infected diet (E+; 1,170 ppb of ergovaline), or E+ supplemented with M (15 mg/kg of lamb BW; E+M). Ad libitum DM intake and digestibility were lower (P 0.05) for E+ than for E- diet. Supplementation of E+ with M increased (P 0.05) DM intake by 27.6% but did not change DM digestibility. Body temperature increased (P 0.05) when lambs consumed E+ and was further increased when M was supplemented. For Exp. 2, 19 wether lambs (average weight 24 kg) were allotted to treatments to evaluate the effects of endophyte consumption (0 vs 2,430 ppb of ergovaline) and supplementation with M (0 vs 20 mg/kg BW). An interaction (P 0.05) of main effects was measured for DM intake. Lambs that consumed E+M consumed more DM than did lambs fed only E+, but lambs offered the E- diet and supplemented with M did not increase DM consumption. Diet DM digestibility was not different among treatments. Skin vaporization decreased (P 0.05) due to E+ consumption and M supplementation. The concentration of prolactin in plasma was decreased (P 0.05) by consumption of E+ (8 vs 136 ng/mL) and did not increase due to M supplementation. Results suggest that supplementing E+ diets with the dopamine antagonist M resulted in increased DM consumption but did not alleviate the lambs' inability to dissipate body heat through skin vaporization