Vasoconstrictive responses of the testicular and caudal arteries in bulls exposed to ergot alkaloids from tall fescue1

Color Doppler ultrasonography was used to evaluate vasoconstrictive responses of the testicular artery in yearling bulls to ergot alkaloids (Neotyphodium coenophialum) produced by a fungal endophyte that infects tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. Alkaloid-induced constriction of the testicular artery could disrupt thermoregulation. Luminal areas of the testicular artery were monitored and analyzed for 2 experiments that were designed to evaluate fertility responses of bulls to toxic endophyte-infected tall fescue. Experiment 1 (pen experiment) compared diets containing toxic endophyte-infected or endophyte-free tall fescue seed, and Exp. 2 (grazing experiment) compared grazing diets consisting of toxic endophyte-infected and nontoxic endophyte-infected tall-fescue pasture. In Exp. 1 ultrasound images were acquired on 3 dates during the 126-d of feeding and in Exp. 2 on 4 dates during the 155-d of grazing. Luminal area of the caudal artery also was monitored as an indicator of alkaloid-induced vasoconstriction. Caudal and testicular arteries for the toxic treatment responded similarly between experiments. Across imaging dates for Exp. 1, caudal artery lumens for the toxic diet averaged 42% less (P < 0.01) area than the nontoxic diet, and testicular arteries for the toxic diet averaged 40% less (P < 0.05) area than the nontoxic diet. For Exp. 2, there were interactions (P < 0.05) between treatment and imaging date on luminal areas of both arteries. Differences between treatments were not detected until the last 2 image dates, with luminal areas of caudal and testicular arteries on the last date for the toxic tall fescue being 46 and 41%, respectively, less than the nontoxic counterpart. Results indicated that ergot alkaloids can induce constriction of blood flow to the testes that may adversely affect bull fertility.