Relationship between acrosome integrity changes and in vitro fertilising ability of bovine spermatozoa

This study was designed to investigate the characteristics of acrosomal changes during capacitation of bovine spermatozoa in relationship to in vitro fertility of individual bulls. Motile spermatozoa were separated from frozen-thawed semen by a swim-up procedure and capacitated in IVF-TALP medium with or without heparin. The spermatozoa were evaluated in terms of acrosomal changes at 0, 3, 4, 5, 6 and 8 h of capacitation. Proportions of acrosome-reacted spermatozoa at 5 h and 0 h of capacitation were used for calculation of the heparin response index. Variations in the heparin response index were found among individual bulls. Based on the mean response index value of all bulls, they fell into three categories: bulls with greater, intermediate and no response to heparin (GRH, IRH and NRH, respectively). Differences in the heparin response index between the bull categories were significant (P < 0.05). Higher D7 and D8 embryo development rates were found in the IRH vs. NRH bulls (P < 0.05). In conclusion, this study shows that the spermatozoa of bulls with a greater or intermediate response to heparin appear to be most suitable for in vitro embryo production compared with spermatozoa of bulls with no response to heparin.