Performance and Fertility of Yearling Beef Bulls Grazing Endophyte-Infected Tall Fescue Pastures

During a two-year study, 80 bulls and 80 steers were utilized to determine the effects of grazing endophyte-infected tall fescue on growth performance, semen parameters, endocrine profiles, and IVF. Bulls and steers were allotted to graze Kentucky 31 tall fescue (Festuca arundinacea Schreb.) infected with Neotyphodium coenophialum, an ergot alkaloid-producing fungal endophyte new stand (E+New; n = 20/yr), old stand (E+Old; n = 20/yr), E+Old plus ladino (Trifolium repens) and red (T. pratense) clovers (E+Cl; n = 20/yr), or Jesup tall fescue with the non-ergot alkaloid-producing endophyte MaxQ (MaxQ; n = 20/yr). Bulls and steers were grouped by body weight (303 ± 13.5 and 290 ± 10.5 kg, respectively), breed composition, hip height, scrotal circumference (SC; 28 ± 1.6 cm), and age (296 ± 20.2 d) to graze assigned pastures from mid-November to the end of June (224 d) each year. Blood samples, ADG, SC and rectal temperatures (RT) were collected every 14 d. Hair coat score (HC) was measured at the end of the experimental period (June). Semen was collected every 60 d (January, March, May, and June). Scrotal temperatures (ST) were obtained by thermography before semen collection in May and June. Semen was evaluated for gross motility, morphology, and ability to fertilize oocytes in vitro (IVF). After motility and morphology examinations, semen was diluted with Bioxcell extender and maintained at 4C until fertilization of oocytes (26 h after semen collection). Oocytes (~850 / treatment) were matured for 22.5 h and fertilized with the identical number of motile percoll-prepared sperm for each treatment. Numbers of putative zygotes that cleaved and developed to blastocyst iv stage (including nuclei number) were evaluated on d 3 and 8 post-fertilization, respectively. The whole experiment was divided into three different analyses for optimal evaluation of treatment differences. Analysis I evaluated performance of bulls (40 / yr) and steers (40 / yr) among all treatments pastures. Analysis II evaluated performance and fertility parameters of bulls (40 / yr) among all treatment pastures. Analysis III examined the ability of sperm from bulls (6 / yr) grazing E+ and MaxQ tall fescue pastures to fertilize oocytes in vitro. Data were arranged in a CRD split-plot repeated measures and analyzed using mixed model procedure that included treatment, season, year, pasture (treatment), and all interactions as fixed effect. These procedures were used to compare differences among treatment for Analysis I and II. Time was a repeated measures factor and animal (treatment x pasture) was included as a random effect. Differences in individual least squares means were evaluated using LSD. Analysis I: Bulls and steers grazing E+New, E+Cl, and E+Old pastures had increased overall RT (P < 0.0001), increased HC (P < 0.0001), and decreased prolactin (P < 0.0001) compared to animals grazing tall fescue MaxQ pastures. Steers grazing E+Cl, E+New, and E+Old pastures had decreased ADG (P < 0.0001) compared to steers grazing MaxQ tall fescue pastures. Moreover, bulls grazing E+New and E+Old had decreased ADG (P < 0.0001) compared to bulls grazing MaxQ and E+Cl pastures. Analysis II: Bull performance on assigned pastures were reported previously in Analysis I. In addition, bulls grazing E+Old had lower ST (32.5 ± 0.4 vs 33.5 ± 0.4 C, P < 0.0001) compared to bulls grazing