Seasonality and freezability vs routine parameters in stallion semen

The fertilizing ability of stallion semen was analyzed using fresh and frozen samples, obtained before (June-July) or during (October-November) the breeding season. Thirty ejaculates obtained from 4 stallions were used. The analysis comprises routine seminogram; ATP concentration (Comhaire et al., 1983); subjective and objective motility and sperm velocity (Makler, 1980). Freezing was done following the technique of Martin et al. (1979). Sperm velocity, ATP content and objective motility in ejaculates of subjective motility >50% show values of 14.0 + or - 0.84 mu m s(-1); 4.8 + or - 2.7x10(-7)M and 54.0 + or - 7.4%, respectively. For ejaculates with subjective motility <50%, these values are 8.4 + or - 2.4; 0.74 + or - 0.36x10(-7)M and 27.0 + or - 0.8%. No significant changes in these characteristics were elicited by freezing, though ATP content dropped to 50% after thawing. These characteristics are highly associated between them (p<0.05) and with some conventional parameters of the routine seminogram such as sperm motility, count, total spermatozoal number and morphology. Additionally, sperm chromatin packing was analyzed by decondensing sperm nuclei using a thiol reducing agent. This parameter was not modified by freezing and it may depend on prolonged epididymal sperm storage during the non-breeding season. Epididymal maturation then results in an excessive disulphur bridging in sperm basic proteins, so that hypermaturation with faulty male pronuclear formation can follow.