Seasonal rhythm of semen characteristics of a Brazilian breed (“Mangalarga”) stallion.

This study explores the seasonal variations of three semen characteristics – ejaculate volume, sperm motility, and sperm count – in a 21-year-old Mangalarga stallion from Brazil over a period of 36 months. The results showed that there were annual fluctuations in these parameters, with the highest semen volume noted in spring (October) and the highest sperm concentration and motility seen in autumn (May).

Research Objective

• The primary aim of this study was to determine the seasonal variations in the semen characteristics of a Brazilian horse breed, the Mangalarga stallion. The researchers endeavored to establish if there were cyclical changes in the ejaculate volume, sperm motility, and sperm count in this breed over a year. This investigation was conducted over a time span of three years, from January 1990 to December 1992.

Research Methodology

• The subject of study was a 21-year-old Mangalarga stallion housed under natural light and climate conditions on a farm in São José do Rio Pardo, São Paulo, Brazil. The horse was fed twice daily with nutritionally balanced feed and had ad libitum access to water and mineral supplements.
• The researchers collected almost daily semen samples using an artificial vagina. Subsequently, the ejaculate volume, sperm motility, and sperm count were measured for each sample.
• In terms of data analysis, the fast Fourier transform (FFT) and Cosinor techniques were employed, with the Cosinor study designed to detect annual rhythms (tau=365 days).

Research Findings

• The study highlighted statistically significant annual rhythms in the semen parameters evaluated. Specifically, the ejaculate volume peaked in the spring (October), whereas the sperm motility and concentration were at their highest levels during autumn (May).
• These results provide critical insights into the reproductive biology of the Mangalarga stallion, specifically the cyclical variations in seminal characteristics. This knowledge could potentially be used to optimize breeding programs for this horse breed in the Southern Hemisphere.