|Rosenkrans jr, C|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/29/2008
Publication Date: 2/18/2009
Citation: Looper, M.L., Rorie, R.W., Person, C.N., Lester, T.D., Hallford, D.M., Aiken, G.E., Rosenkrans Jr, C.F. 2009. Influence of toxic endophyte-infected fescue on sperm characteristics and endocrine factors of yearling Brahman-influenced bulls. Journal of Animal Science. 87:1184-1191. Interpretive Summary: Minimal research exists for the negative effects of toxic tall fescue on bull reproductive performance. In natural breeding, reduction in performance of one bull could decrease the pregnancy rate of 20 to 25 cows. Scientists from ARS in Booneville, AR, the University of Arkansas, and New Mexico State University investigated the influence of fescue type on sperm characteristics in bulls. Bulls grazed either toxic or nontoxic fescue, and semen and scrotal circumference were measured monthly. Semen from bulls grazing toxic fescue had reduced motility compared with bulls grazing nontoxic fescue pastures. Effects of toxic fescue on semen quality were intensified by increased maximum daily temperatures that occur during summer. Beef producers should minimize the use of toxic fescue during the breeding season especially during warmer times of the year. Use of nontoxic forage diets or grain supplementation during the breeding season will alleviate the detrimental effects of toxic fescue on bull performance. This information is important to livestock producers and extension personnel.
Technical Abstract: Sixteen (mean age = 1.1 +/- 0.1 yr; mean BW = 478 +/- 34 kg) Brahman-influenced bulls were used to determine the influence of fescue type on sperm characteristics and serum concentrations of prolactin, cortisol, and testosterone. Bulls were blocked by BW, scrotal circumference (SC), and pregrazing sperm characteristics and randomly assigned to graze either toxic endophyte-infected (EI; 4 bulls/pasture; 2 pastures) or novel endophyte-infected (NE; 4 bulls/pasture; 2 pastures) tall fescue for 121 d. Semen was collected by electroejaculation, and SC was measured and blood samples collected monthly. Sperm were evaluated for motility and morphology with an integrated visual optical system. Overall mean concentration of prolactin was decreased more (P < 0.01) in EI bulls than NE bulls from May to August. Scrotal circumference was not affected by fescue type (P = 0.58). There were no differences (P > 0.10) between fescue types for sperm characteristics prior to July and August. Bulls grazing NE fescue had more (P < 0.06) motile sperm than EI bulls. Percentages of progressive (57 vs 38%, NE and EI, respectively; P < 0.06) and rapid (67 vs 46%, NE and EI, respectively; P = 0.04) sperm were greater from bulls grazing NE than EI bulls. Average velocity of the smoothed sperm path and progressive velocity in a straight line from the beginning to the end of the sperm track were slower (P < 0.09) in EI bulls than NE bulls and were slower (P = 0.04) in August compared to July. Mean width of head oscillation as the sperm swims was less (P < 0.06) in August than July. Concentrations of cortisol and testosterone were not (P > 0.10) influenced by fescue type. Semen from bulls grazing EI had reduced motility and morphology than bulls grazing NE. Detrimental effects of toxic fescue may not be mediated by cortisol and (or) testosterone. Effects of EI on semen quality were exacerbated by increased maximum ambient temperatures.