French field results (1985-2005) on factors affecting fertility of frozen stallion semen.

This research paper provides insight into the factors affecting the fertility of stallion semen after freezing and its application in insemination programs, based on French field data collected over a period of two decades (1985-2005). The report also highlights the need for uniform guidelines regarding frozen semen use within the European Community.

Research Parameters and Procedures

• The study observed the system implemented in the French National Stud, which encompassed specific procedures for freezing semen, selection of ejaculates, and insemination protocols.
• The freezing protocol involved dilution in milk, centrifugation, and the addition of a freezing extender at a specific temperature, followed by cooling and freezing at defined rates.
• The study involved only the ejaculates that showed a high (>35%) post-thaw motility, i.e., the capability of sperm to move efficiently after being thawed from a frozen state.
• The insemination protocol consisted of examining mares once daily and performing artificial insemination (AI) twice, 24 hours apart, before ovulation.

Key Findings and Results

• The research applied to over 110 stallions per year with an average of 50% post-thaw motility detected in ejaculates prior to selection.
• The fertility or “freezability” of the semen was analyzed as the ratio of selected ejaculates to the total number of ejaculates frozen. Various levels of freezability were observed across the stallions.
• The per-cycle pregnancy rate with AI was found to be 45-48% compared to a 57-59% rate when mares were hand-mated to stallions.
• The foaling rate (i.e., the rate at which mares gave birth to live foals) was consistent at around 64% regardless of the insemination method.

Improving Fertility with Frozen Semen

• The results show that using low glycerol concentration, a suitable base extender for freezing, maintaining high post-thaw motility, and providing a sufficient number of spermatozoa per mare for the breeding season can improve the fertility success rate.
• Providing lower numbers of spermatozoa per cycle may result in a lower per-cycle pregnancy rate and higher costs in mare management.

Recommendations

• This study highlights a need for uniform regulations on the quality and quantity of frozen equine semen within the European Community to ensure optimized use and fertility results.
• The researchers suggest a codification based on crucial parameters like the number of spermatozoa available per mare per season, the post-thaw motility, and the final glycerol concentration.