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Factors affecting spermatozoa morphology in beef bulls

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The objective of this study was to evaluate factors affecting sperm morphology of bulls (n=908) collected at 320 days of age. Bulls were a composite breed (50% Red Angus, 25% Charolais, and 25% Tarentaise) born from 2002 to 2008 to dams fed levels of feed during mid and late gestation that were expected to provide marginal or adequate nutrition while grazing dormant winter forage. After weaning, bulls were fed to appetite (CON) or restricted (REST) to 80% of that consumed by CON on BW basis. Semen samples were collected using an electroejaculator and evaluated using standard BSE procedures. Spermatozoa morphology was evaluated by classifying 100 spermatozoa per bull at 400 X magnification into the following categories: normal spermatozoa, knobbed acrosome, head defects, distal midpiece reflex, dag defect, bowed midpiece, proximal droplet, distal droplet, coiled principle piece, and bent principle piece. Each morphological trait, along with scrotal circumference (SC), gross motility, and percent progressive motility was analyzed using MTDFREML and pedigree information from 8163 relatives born from 1974 to 2008 to provide heritability estimates. Heritability estimates for these traits were: SC (h2 = 0.67), normal sperm (h2 = 0.18), dag defect (h2 = 50), bowed midpiece (h2 = 0.19), proximal droplets (h2 = 0.37), bent principle piece (h2 = 0.18), gross motility (h2 = 0.20), and progressive motility (h2 = 0.20). The moderate heritability of percent normal sperm and several of the other sperm defects suggest that selection for improved sperm morphology is possible. Further analysis with MTDFREML determined genetic correlations between the above traits and pre-weaning gain direct, pre-weaning gain maternal, post-weaning gain, and scrotal circumference. Maternal pre-weaning gain was highly correlated with scrotal circumference (r = 0.70 ± 0.24) but pre-weaning gain direct (r = 0.29 ± 0.20) and post-weaning gain (r = 0.01 ± 0.17) were not. Scrotal circumference and post-weaning gain were not highly correlated with morphology and therefore are not good indicators of spermatozoa morphology. Neither in utero nor postweaning diet affected any of the traits measured.
Roberts, C.A. , Geary, T.W. , MacNeil, M.D. , Waterman, R.C. , Roberts, A.J. , Alexander, L.J.
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Proceedings / Western Section, American Society of Animal Science 2010, v. 61
Journal Articles, USDA Authors, Peer-Reviewed
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