Effect of the knobbed acrosome defect in bovine sperm on IVF and embryo production

An IVF and culture system was used to determine the effect of the knobbed a crosome defect in bovine spermatozoa on fertilization and early embryonic d evelopment. Three bulls affected with knobbed acrosomes were identified as K+ (flattened acrosome), K2+ (indented acrosome) or K3+ (deep indentation o f the acrosome) based on the predominant type of acrosomal aberration prese nt in sperm of the respective bulls. After swim-up, all semen traits, excep t for acrosome morphology, were similar between bulls with varying degrees of the knobbed acrosome defect and a control bull, C. The mean number of sp ermatozoa bound to the zona pellucida was lower (P < 0.05) for the bulls wi th the knobbed acrosome defects (40.3 +/- 2.3, 29.5 +/- 1.6, 14.6 +/- 1.3, respectively, for Bulls K+, K2+ and K3+) than for Bull C (52.3 +/- 2.3). Th e percentages of zonae pellucidae penetrated by spermatozoa from Bulls K+ ( 51.2%), K2+ (49.5%) and K3+ (37.1%) were lower than that of Bull C (84.5%). No sperm with knobbed acrosome defects were found to have penetrated the z ona pellucida. Fertilization rates for bulls with the knobbed acrosome defe ct, K+ (63.0%), K2+ (62.7%) and K3+ (22.6%), were significantly lower than that of the control bull (82.8%). Percentages of cleaved embryos, morulae a nd blastocysts produced were also lower for the bulls with knobbed acrosome s than that of the control bull. Results indicate that sperm with the knobb ed acrosome defect had a reduced ability to bind to the zona pellucida, dep ending upon the severity of the defect, and that these aberrant spermatozoa did not penetrate the zona pellucida. The apparently normal spermatozoa co existing in the inseminate of bulls with a high percentage of knobbed sperm atozoa were also functionally deficient; oocytes penetrated by these sperma tozoa had a reduced potential for fertilization, and resulting zygotes had a reduced ability for cleavage and embryonic development to the blastocyst stage. The results of the present study do not support the hypotheses that the knobbed acrosome defect is compensable. (C) 2000 by Elsevier Science in c.