In vitro aging of frozen bull semen

Area of Science:

• Veterinary Science
• Reproductive Biology
• Animal Science

Background:

• Bull semen fertility is crucial for artificial insemination (AI) programs.
• Understanding the impact of long-term cryopreservation on semen viability is essential for optimizing breeding strategies.

Purpose of the Study:

• To examine the change in bull semen fertility over extended storage periods at -196°C.
• To determine the optimal storage duration for maintaining high nonreturn rates in bull semen.

Main Methods:

• Analysis of 97,586 first inseminations from the Michigan Animal Breeders Cooperative over 5 years.
• Grouping semen storage intervals by 10, 30, 180 days, and 4-5 years.
• Calculation of nonreturn rates at 50-, 60-, 90-, and 180-day intervals post-breeding.

Main Results:

• Nonreturn rates increased with storage time, reaching a plateau around 115 days.
• Semen viability remained consistent through the 4 and 5-year storage groups.
• Differences in nonreturn rates between storage intervals were approximately 4%, with maximum variations at lower rates.

Conclusions:

• Cryopreserved bull semen maintains fertility for up to 5 years at -196°C.
• Storage duration beyond 115 days shows minimal negative impact on nonreturn rates.
• Long-term semen storage is a viable strategy for maintaining genetic diversity and improving AI efficiency.