PARENT SESSION

(W690) SUSCEPTIBILITY OF BOVINE SPERM TO THE IN VITRO INDUCED ACROSOME REACTION.

Birck, Anders¹, Moeller Petersen, Morten¹, Christensen, Preben¹, ¹ The Royal Veterinary and Agricultural University, Frederiksberg, Copenhagen, Denmark

ABSTRACT- The susceptibility of bovine sperm to the in vitro induced acrosome reaction was investigated. Post-thaw sperm from 4 bulls (A-D) were assessed for their ability to acrosome react in response to calcium-ionophore (A23187 1 M). After thawing sperm were washed and incubated for 45 min at 38.5°C, 5% CO₂ in a capacitating medium containing heparin, hypotaurine, epinephrine, and calcium-ionophore or in a non-capacitating medium containing calcium ionophore only. Viability and acrosome status were assessed by flow cytometry using the triple fluorochrome combination of SYBR14, propidium iodide, and phycoerythrin-conjugated peanut agglutinin. Acrosome inducibility after incubation was defined as the percentage of live acrosome reacted sperm versus all live sperm. For each bull acrosome inducibility in capacitating and non-capacitating medium was compared. As control, incubation was done in both media without calcium-ionophore. However, for all bulls spontaneous acrosome reactions in the live population were low (<3%). All experiments were done in triplicates. Acrosome inducibility in capacitating medium containing calcium-ionophore: A 59%±3.6, B 46%±2.9, C 61%±8.0, D 67%±3.8. Acrosome inducibility in non-capacitating medium containing calcium-ionophore: A 57%±9.6, B 29%±7.8, C 38%±5.5, D 35%±9.8. Sperm from bull B, C, and D incubated under capacitating condition with calcium-ionophore had significantly enhanced acrosome inducibility when compared to the non-capacitating conditions (P<0.05, paired t-test). Maximum level of acrosome inducibility was not equal. Under capacitating conditions maximum for bull B was significant lower (P<0.05, one-way ANOVA). Under non-capacitating conditions the acrosome inducibility of bull A was significant higher than for bull B and D (P<0.05, one-way ANOVA). Interestingly, acrosome inducibility of bull A did not differ between the incubating conditions. This experiment indicates that differences in capacitating conditions to enhance the induced acrosome response may exist between bulls. These individual differences in the dynamics of the induced acrosome reaction could contribute to variation of fertility. However, the importance of the in vitro induced acrosome reaction as a predictor of fertility needs further examination.

KEY WORDS: sperm, acrosome reaction, capacitation, flow cytometry