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

摘要

Sixteen (mean age = 1.1 ± 0.1 yr; mean BW = 478 ± 34 kg) Brahrnan-influenced bulls were used to determine the influence of fescue type on sperm characteristics and serum concentrations of pro-lactin, cortisol, and testosterone. Bulls were blocked by BW, scrotal circumference (SC), and pregrazing sperm characteristics and randomly assigned to graze toxic endophyte-infected (El; 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 El bulls than NE bulls from May to August. Scrotal circumference was not affected by fescue type (P 0.58); overall SC averaged 36.7 + 2.3 cm. Percentage of live sperm was not different (P = 0.24) between NE bulls (80%) than El bulls (67%) in July and August. Bulls grazing NE fescue had more (P < 0.06) motile sperm than El bulls in July and August. Percentages of progressive (57 vs. 38%, NE and El, respectively; P < 0.06) and rapid (67 vs. 46%, NE and El, respectively; P = 0.04) sperm were greater from bulls grazing NE than El bulls in July and August. 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 El bulls than NE bulls and were slower (P = 0.04) in August compared with July. Mean width of head oscillation as the sperm swims was less (P 0.10) influenced by fescue type. Semen from bulls grazing El had reduced motility and morphology than bulls grazing NE. Detrimental effects of toxic fescue may not be mediated by cortisol, testosterone, or both. Semen quality of bulls grazing toxic El tall fescue was decreased with increased maximum ambient temperatures. [PUBLICATION ABSTRACT]