Fertility of stallion semen frozen in 0.5-ml straws.

The research evaluates the fertility rates of frozen stallion semen used to inseminate mares. It concludes that simpler freezing techniques with a post-thaw progressive motility of 30% can yield satisfactory pregnancy rates if at least 220 million progressively motile spermatozoa are used for every second-day insemination until ovulation is confirmed.

Methodology

• The study used the semen of two pony stallions, which was frozen using two different methods in 0.5 ml PVC straws.
• The frozen semen was then thawed and used to inseminate 60 mares during 69 oestrous cycles to evaluate its fertility.

Results

• An overall single cycle pregnancy rate of 55% was achieved using these methods.
• The study established that the method of freezing, the stallion from which the semen was collected, and the timing of insemination (during steroid-synchronized oestrus or only every second day during oestrus) did not have a significant impact on pregnancy rates.

Significant Findings

• The pregnancy rates improved significantly, from an average of 44% to 73%, when the average number of progressively motile spermatozoa used for insemination increased from 175 million to 249 million.
• The study concluded that simpler freezing techniques can yield satisfactory pregnancy rates. The prerequisite, however, is that the semen demonstrates a post-thaw progressive motility (the ability to move in a forward or linear direction) of 30% and is used for artificial insemination (AI).

Recommended Protocol

• For optimum results, mares should be inseminated every second day, starting when ovulation is expected to occur within the next 48 hours. This insemination schedule should continue until ovulation is confirmed.
• A minimum of 220 million progressively motile spermatozoa should be used for each insemination session.

This research implies that by carefully managing freezing methods and insemination protocols, equine breeders can attain satisfactory pregnancy rates even when using frozen stallion semen. It underlines the importance of having an adequate number of progressively motile spermatozoa during insemination to improve pregnancy outcomes.