469 Veterinarni Medicina, 60, 2015 (9): 469–475 Original Paper doi: 10.17221/8437-VETMED Relationship between acrosome integrity changes and in vitro fertilising ability of bovine spermatozoa Z. Reckova 1 , M. Machatkova 2 , L. Machal 1 , M. Jeseta 2 1 Mendel University, Brno, Czech Republic 2 Veterinary Research Institute, Brno, Czech Republic ABSTRACT: 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. Keywords: bull; spermatozoa; acrosome; embryos; IVF Supported by the Ministry of Education, Youth and Sport of the Czech Republic (Projects No. FA MENDELU IGA TP 5/2014 and No. LD14104 COST-CZ). A necessary prerequisite for efficient in vitro em- bryo production is a sufficient number of motile acrosome-intact sperm capable of fertilising the oocyte. Different separation methods are used for the preparation of a population of motile spermatozoa from frozen-thawed bull semen, with swim-up be- ing one of the most commonly used techniques for sperm isolation. This process enables the selection of a population of viable spermatozoa with intact acrosomes (Alomar et al. 2006). At the same time, a high proportion of motile spermatozoa must be able to undergo the acro- somal reaction at the appropriate time to ensure efficient fertilisation of the oocyte. In order to in- duce the acrosome reaction, culture media for in vitro fertilisation are supplemented with different capacitating agents, preferentially with heparin, which has a capacitating effect on bovine sperma- tozoa (Van Soom and de Kruif 1996; Pereira et al. 2000; Mendes et al. 2003). Sumantri et al. (1996) demonstrated that under uniform capacitation conditions, the proportion of sperm capacitated at the same time is highly variable depending on the bull breed. A number of studies have focused on the evalu- ation of acrosome status (Kitiyanant et al. 2002; Puente et al. 2011; Almadaly 2012), sperm capaci- tation and variations among different bull breeds (Demyda-Peyras et al. 2012). There are also nu- merous studies concerned with the high variability in embryo production under in vitro conditions, using spermatozoa from different bulls, but only a few studies have investigated a potential relation- ship between the in vitro-induced acrosome reac- tion and in vivo fertility of bulls (Whitfield and