Fertility aspects in yearling beef bulls grazing endophyte-infected tall fescue pastures

Abstract

During a 2-year study, yearling beef bulls were used to determine the effects of grazing on endophyte-infected 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 (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.

Influence of toxic endophyte-infected fescue on sperm characteristics and endocrine factors of yearling Brahman-influenced bulls1,2

“…Changes in sperm quality between bulls grazing toxic EI or NE fescue pastures were detected only after ambient temperatures increased in July and August. Differences between Schuenemann et al (2005a) and the current study also may be attributed to laboratory methodologies; Schuenemann et al (2005a) used subjective procedures, whereas an IVOS analysis was used in the current experiment. Sperm motility of Holstein bulls ranged from 62 to 69% with subjective procedures, whereas the range was 52 to 82% for computer-assisted sperm analysis; repeatability was 0.99 for computer-assisted sperm analysis (Farrell et Major defects = malformed, abnormal acrosome, proximal droplet, folded tail, midpiece defect, cratered head, pyriform head, or small/giant head.…”

“…In the current experiment, percentage of rapid progressive sperm was decreased in EI compared with NE bulls in July and August. Schuenemann et al (2005a) reported that although sperm motility and morphology did not differ between bulls grazing toxic EI or NE fescue pastures from November to June, potential of sperm to fertilize oocytes was reduced from bulls grazing toxic EI fescue. Similarly, we did not detect differences in sperm motility in May and June.…”

Identification of bovine prolactin in seminal fluid, and expression and localization of the prolactin receptor and prolactin-inducible protein in the testis and epididymis of bulls exposed to ergot alkaloids

“…The toxins produced by many cultivars of tall fescue containing mutualistic endophytes are ergot alkaloids and are potent dopaminergic agonists. Consumption of ergot alkaloids clearly suppresses serum PRL concentrations in bulls [30,31,40,46]. Prolactin is known to be present in the human seminal fluid [13,14], so we evaluated its presence and determined if the levels of PRL in seminal fluid were impacted by the consumption of ergot alkaloids.…”

Physiological Basis of Fescue Toxicosis

“…Reproductive effects have been noted in several species consuming E+ tall fescue, including mice, rabbits, horses, sheep, and cattle (Daniels et al, 1984;Boling, 1985;Zavos et al, 1987;Bond et al, 1988;Monroe et al, 1988;Porter and Thompson, 1992;Jones et al, 2003;Schuenemann et al, 2005). Ruminants typically have reduced conception rates and, thus, reduced reproductive efficiency.…”