Variations in structural and functional changes of stallion spermatozoa in response to calcium ionophore A23187

Three experiments were conducted to assess the structural and functional changes of stallion spermatozoa in response to the calcium ionophore A23187, and to determine individual variation between stallions. In Experiment 1, changes in the acrosome of spermatozoa exposed to 7.14 microM A23187 for fixed times between 0 and 120 min were examined. There was a steady increase with time in the number of spermatozoa undergoing the acrosome reaction although the rate of increase differed between stallions. Sperm motility decreased sharply when incubation was extended beyond 30 min. In Experiment 2, the ability of ionophore-treated spermatozoa to penetrate zona-free hamster eggs was tested. Percent penetration rates were 75, 50, 28, 27 and 15 for the 5 stallions although the number of swollen sperm heads per penetrated egg (1.7-2.5) did not differ significantly between the stallions. In Experiment 3, the ability of stallion spermatozoa to fertilize zona-intact follicular horse eggs matured in vitro was tested. Semen samples from the 2 stallions that provided the highest and lowest percent acrosome-reacted spermatozoa in Experiment 1, and the highest and lowest penetration rates in Experiment 2, were separated from seminal plasma and treated with 5 microM A23187 for 10 min. The spermatozoa were then washed once and co-incubated with the eggs at 38.5 degrees C for 12-16 h. Swollen sperm heads with associated tails from 1 stallion were found in 8 of 46 eggs fixed after 12-16 h incubation, whereas the corresponding figure for the other stallion was 0/30. It was concluded that considerable individual variation occurs between stallions in the morphological and functional changes exhibited by their spermatozoa in response to treatment with ionophore A23187.