Characteristics and fertility of stallion semen.

This research focuses on understanding the connection between seminal characteristics and fertility in stallions, across seven breeds, using data gathered over four breeding seasons in Eastern Australia. The study identifies certain semen characteristics that are significantly associated with fertility.

Study Setting and Data

• The study was conducted in Eastern Australia on commercial studs over the course of four breeding seasons from 1974-1978.
• Data was extracted from 47 stallions, aged between 2-26 years, representing seven different breeds. This amounted to a total of 1664 mares across 66 breeding seasons.

Fertility Determination

• The researchers used the percentage of pregnancies per service to gauge the stallion’s fertility. This measure was found to be the most sensitive for determining fertility in stallions on commercial studs.

Factors Affecting Fertility

• The age and breed of the stallion, the breeding season, and the stallion’s referral status (either ‘suspect’ or ‘normal’) were variables significantly affecting the stallion’s fertility.
• These factors were found to have a significant difference on fertility levels (P<0.01).

Seminal Characteristics Linked to Fertility

• Notably, certain semen characteristics showed a clear association with the number of pregnancies per service.
• These characteristics include: the total volume of semen, the gel-free volume, the sperm concentration, the total number of spermatozoa (male reproductive cells), and the total number of live spermatozoa.

Potential Diagnostic Implications

• The researchers present approximations for threshold levels of these characteristics, with the intention of providing a diagnostic foundation for the classification of stallions as either suitable or doubtful for breeding purposes.