During a 2- year study, yearling beef bulls were used to determine the effects of grazing on endophyteinfected tall fescue on endocrine profiles, semen quality and fertilisation potential. Bulls were allotted to graze tall fescue pastures infected with Neotyphodium coenophialum ( E+; n= 20 per year) or Jesup/ MaxQ (TM) ( Pennington Seed, Atlanta, GA, USA; NTE; n= 10 per year). Bulls were grouped by scrotal circumference ( SC), bodyweight ( BW), breed composites and age to graze tall fescue pastures from mid- November until the end of June ( within each year). Blood samples, BW, SC and rectal temperatures ( RT) were collected every 14 days. Semen was collected from bulls every 60 days by electroejaculation and evaluated for motility and morphology. The developmental competence of oocytes fertilised in vitro with semen from respective treatments was determined. Bulls grazing E+ pastures had decreased BW gain ( P < 0.01), increased overall RT ( P < 0.01) and decreased prolactin ( P < 0.01) compared with animals grazing NTE pastures. Neither percentage of normal sperm morphology nor motility differed between bulls grazed on the two pasture types. Semen from E+ bulls demonstrated decreased cleavage rates ( P = 0.02) compared with semen from NTE bulls. However, development of cleaved embryos to the eight- cell and blastocyst stages did not differ between the two groups. In conclusion, semen from bulls grazing E+ tall fescue resulted in decreased cleavage rates in vitro, which may lower reproductive performance owing to reduced fertilisation ability.
