Bulls grazing Kentucky 31 tall fescue exhibit impaired growth, semen quality, and decreased semen freezing potential

Authors: PRATT, S - Clemson University; STOWE, H - Clemson University; WHITLOCK, B - University Of Tennessee; STRICKLAND, L - University Of Tennessee; MILLER, M - Clemson University; CALCATERA, S - Clemson University; DIMMICK, M - Clemson University; Aiken, Glen; SCHRICK, F - University Of Tennessee; LONG, N - Clemson University; DUCKETT, S - Clemson University; ANDRAE, J - Clemson University

Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 2/1/2015
Citation: Pratt, S.L., Stowe, H.M., Whitlock, B.K., Strickland, L., Miller, M., Calcatera, S.M., Dimmick, M.D., Aiken, G.E., Schrick, F.N., Long, N.M., Duckett, S.K., Andrae, J.G. 2015. Bulls grazing Kentucky 31 tall fescue exhibit impaired growth, semen quality, and decreased semen freezing potential. Theriogenology. 83:408-414.

Interpretive Summary: Tall fescue is the predominant forage used for grazing in the transition zone between the temperate northeastern and subtropical southeastern regions of the USA. Cow-calf production is substantial in the region, which is problematic because ergot alkaloids produced by a fungal endophyte that infects most plants of tall fescue are toxic and cause a toxicosis in cattle. Of particular economic concern is the negative impact that ergot alkaloids have on conception and calving rates of cow herds. Poor reproductive performance has been linked to declines in body condition and unstable hormone profiles that occur when cows graze toxic tall fescue. There has been little research on the effects of ergot alkaloids on bull fertility, but research conducted by Clemson University and USDA-ARS Forage Animal Production Research Unit found strong evidence that ergot alkaloids reduce sperm quality. Spermatozoa characteristics associated with ergot alkaloids were found to be altered in bulls that were fed alkaloids for 155 days. Sperm in these bulls were in lower concentration and less mobile than those in bulls fed non-toxic diets. This research provides evidence that poor reproduction on toxic tall fescue is because of adverse effects of ergot alkaloids on both the cow and bull, which will be of interest to all cow-calf producers that rely on tall fescue to meet the nutritional needs of their herds.

Technical Abstract: Serum prolactin (PRL) and testosterone concentrations, body weight, body composition, semen quality, and semen freezing potential for bulls grazing the toxic tall fescue (Lolium arundinaceum [Schreb.] Darbysh. ¼ Schedonorous arundinaceum [Schreb.] Dumort.) cultivar Kentucky 31 (E+) compared with a novel endophyte cultivar lacking ergot alkaloids (E-) were evaluated. Angus bulls were allotted to treatment (Day 0) and grazed E+ or E- for 155 days. Treatment-by-day interaction was significant (P < 0.05) for serum PRL concentrations with E+ treated bulls exhibiting reduced PRL values compared with E control bulls, but no differences were observed for serum testosterone concentrations (P > 0.05). Further, bulls on the E+ treatment exhibited decreased total gain, average daily gain, and body weight by Day 140 (P< 0.05) and intramuscular fat in the E- bulls compared with the E+ group was higher by Day 155 (P < 0.05). Analysis of ejaculates showed significant treatment day effects for sperm concentration with lower values observed for bulls on the E+ treatment (P < 0.05). The percent normal morphology was reduced in ejaculates from E+ bulls compared with E- bulls (P < 0.05), and the difference was due to an increase in abnormal sperm present in the E+ ejaculates from Day 84 to 140 (P < 0.05). In addition, spermatozoa motility and progressive motility were decreased on thawing in semen samples from E+ bulls compared with E- bulls (P < 0.05).