PS9-13. Dietary Ergovaline Concentrations Did Not Alter Responses to Haemonchus contortus Infections in Hair Sheep.

Abstract

Gastrointestinal nematodes are a major challenge for small ruminant producers, especially in the southeastern U.S. Immune responses to the barber’s pole worm (Haemonchus contortus) may be compromised by exposure to ergovaline, a toxin encountered in tall fescue (Lolium arundinaceum) infected with wild-type endophyte (Epichloë coenophiala). The objective of this work was to evaluate the effects of dietary ergovaline concentrations on dry matter intake (DMI), average daily gain (ADG), fecal egg counting (FEC), hematocrit (HCT) and rectal temperature (RT) in artificially parasited and nonparasited hair sheep. Fifty-six predominantly Katahdin ewe lambs were randomly assigned (14 animals per treatment) to one of four diets containing increasing concentrations of ergovaline (0, 400, 800 and 1,200 ppb/kg DM). Half of the lambs (7 per treatment, 28 in total) were artificially infected with 10,000 H. contortus infective larvae (L3). The animals, housed in a concrete-floor feedlot (3.8 m2/animal), were group-fed according to their diet treatments using SmartFeed Pro C-LOCK feeders, which record feed intake for individual animals. Upon arrival at the site from a single farm, the ewe lambs (5 months old, 24 kg BW) were dewormed using a triple-class deworming protocol for sheep — benzimidazoles, macrocyclic lactones, and imidazothiazoles, and received a single dose of copper oxide wire particles (2 g). Following a 14-day adaptation period on an ergovaline-free diet, the lambs were offered experimental diets, which varied by the proportion of endophyte-free and Kentucky-31 tall fescue seed, for 56 days. Fecal and blood samples were collected weekly for FEC and HCT analysis. The RT was measured biweekly using a digital veterinarian thermometer. The ADG was calculated biweekly using BW data. Data were analyzed using mixed models with repeated measures. The FEC were log10(FEC + 1) transformed, and results are presented as back-transformed least-squares means. Tukey-adjusted comparisons and polynomial contrasts were used to assess parasite effects and ergovaline dose responses, respectively. The FEC was affected by the parasite × time interaction (P < 0.001). After 3 weeks of infection, parasitized animals presented greater FEC than nonparasitized animals, as expected (490 vs 85 egp, respectively). Ergovaline x time affected DMI, ADG, HCT, and RT. The ADG linearly decreased (P ≤ 0.05) as dietary ergovaline concentration increased during the first 14 days, with no effect thereafter (P > 0.05). Increasing ergovaline concentrations increased HCT quadratically (P = 0.02) on d21 of the study, but decreased it linearly (P = 0.02) on d42. The RT increased linearly with ergovaline concentration (P < 0.04) on d14 and d28 and tended to increase (P = 0.07) on d42. No linear or quadratic effect of ergovaline was observed for DMI (P > 0.05). In conclusion, dietary ergovaline concentrations did not alter responses to H. contortus infections in hair sheep.