The effect of fescue toxicosis on semen quality and fertility of young growing beef bulls

The objective of this study was to evaluate semen quality and fertility in young growing beef bulls grazing the ergot alkaloid (EA) producing tall fescue cultivar Kentucky 31 (KY31) compared to a novel endopyhte cultivar lacking EA (NE). Angus bulls (n = 54 over 2 yr, 12 - 16 mo of age) were stratified by BW, BCS and scrotal circumference (SC) then allotted to graze either KY31 or NE for 56 d. Bulls were subjected to venipuncture and electro-ejaculation at the start of treatment (TRT; d 0) and every 28 d to the end of the study. Semen was evaluated for quality and blood samples harvested for use in prolactin (PRL) RIA. Bull BW, BCS and SC were measured on d 0, 28 and 56. On d 56, semen from bulls (n = 4 per treatment) with similar and acceptable quality was extended, kept at 19^o C, and used for artificial insemination within 30 h of collection. Angus and Angus crossbred females were stratified by age, calving date, BCS and BW and allotted to be timed inseminated (TAI) with KY31 (n = 78) or NE (n = 73) semen. Pregnancy was evaluated 30 d post-timed insemination via transrectal ultrasound to determine TAI pregnancy rates. Bull BW, BCS, serum PRL concentration, and all semen quality parameters were subjected to analysis using JMP (SAS Institute, Cary NC) with the LS Means procedure to test for effects of TRT, day, and TRT x day interactions. Serum PRL concentrations showed a TRT x day effect (P = 0.001) with values for bulls grazing KY31 decreased at 28 and 56 d of grazing compared to NE. Bull BW and BCS were affected by d (P = 0.001). Neither the ejaculate volume, sperm concentration, or sperm velocity differed due to TRT. Both percent motile sperm (P = 0.03) and progressively motile sperm (P = 0.04) were lower in the KY31 at d 0 compared to the other TRT x day combinations; however, no difference was observed in the percentage of bulls passing a breeding soundness exam due to TRT. Timed AI pregnancy rates were 46 and 43% for KY31 and NE, respectively (P = 0.655). Grazing KY31 negatively impacts serum PRL concentrations and supports previous observations; however, consuming KY31 had no effect on growth, semen quality or fertility of young growing beef bulls.