Effect of timing of insemination, numbers of spermatozoa and extender components on the pregnancy rate in mares inseminated with frozen stallion semen.

The research article examines the factors impacting the pregnancy rate in mares when inseminated with frozen stallion semen. The findings suggest that the timing of insemination, sperm count, and specific semen extender components play a crucial role in enhancing the fertilization and foaling rates.

Effect of Insemination Timing and Sperm Count

• The study shows that the pregnancy rate was highest in mares when inseminated using frozen semen within 12 hours of ovulation. This suggests that precise timing of insemination relative to ovulation is a significant factor for successful fertilization.
• With regard to sperm count, the research revealed that foaling rate improved by increasing the quantity of motile (active) spermatozoa from 40 X 10(6) to 80 X 10(6). However, further increase of the count to 160 X 10(6) or increasing the frequency of insemination from once to twice daily did not bring any additional improvement.

Role of Extender Components

• Extenders are additives used to preserve sperm viability in the freezing process. The research found that the effectiveness of spermatozoa frozen in certain hydrogen ion extenders was influenced by relative osmotic pressure and freezing method.
• Adjustments to the glycerol concentration, specifically reducing it from 7% to 2%, improved the fertilizing capacity of the spermatozoa. Addition of glycerol 15 minutes before freezing and freezing 2 hours after extension also boosted sperm fertility.

Comparison between Extended and Unextended Semen

• Interestingly, the study found that mares inseminated with unextended semen had higher pregnancy rates (75%) than those inseminated with extended semen that either contained no glycerol (50%) or 7% glycerol (35%).
• In all cases, the pregnancy rate was lower when the semen was extended or extended and frozen, when compared to stallions’ natural fertility rates. These findings emphasize the effect of the extension process on the fertilizing capacity of spermatozoa.

Conclusions

• The researchers concluded that hydrogen ion extenders reduce the fertilizing capacity of stallion spermatozoa immediately after extension, hence demonstrating low potential as effective semen extenders for both short- or long-term storage of stallion semen.

The study’s results suggest that further optimization of the preserving and freezing process is necessary to maximize the chances of successful insemination with frozen stallion semen.