Seasonal variations in stallion sperm features and their relationship with fertility of the breeding stock

Abstract

Seasonal influence upon spermatozoal concentration, progressive motility and percentage of morphologic abnormalities in the semen of horses was studied, and the fertility of the breeding stock during the corresponding breeding season was assessed. The semen of 7 stallions was collected monthly during 12 months for microscopic examination, and the matings were made by natural service. The highest spermatozoal concentration was recorded during autumn and the lowest, during spring. Along the months, the highest records were those in July and the lowest, in June, but no significant statistical differences were found for the seasonal and monthly variations. The highest rate of progressive motility was observed during summer and the lowest, during spring. Among the months, July presented the highest rate and April the lowest. Differences were significative between months (p < 0,05) and between seasons (p < 0,10). The highest rate of sperm morphologic abnormalities was recorded in summer (p < 0,05). January presented the highest rates of abnormal cells and March the lowest, but the differences among months were not statistically significant. During the breeding season, the fertility of the stock measured by pregnancy rate per cycle increased in a linear manner from 29% in October to 95% in February, not showing any apparent relationship with the seminal characteristics studied.