Double artificial insemination in sheep: a comprehensive review

Area of Science:

• Reproductive biotechnology in livestock.
• Animal science and veterinary medicine.

Background:

• Artificial insemination (AI) in sheep yields variable results, particularly during anestrus with estrus induction.
• Improving AI efficiency without increasing costs is crucial for sheep production systems.
• Double AI is a potential strategy to enhance reproductive outcomes.

Purpose of the Study:

• To review existing literature on double-cervical AI in sheep.
• To identify knowledge gaps regarding double AI techniques.
• To assess the efficacy of double AI compared to single AI.

Main Methods:

• Literature review of studies on double-cervical AI in sheep.
• Analysis of pregnancy rates (PR) from studies comparing single and double AI.
• Evaluation of results based on semen type (frozen-thawed, fresh, chilled) and AI timing (estrus detection vs. fixed-time).

Main Results:

• Double cervical superficial AI with frozen-thawed semen after estrus detection significantly increased PR in most studies (6/8), by 7 to 34.2 percentage points.
• Double fixed-time AI (FTAI) using fresh or chilled semen did not show positive effects in most cases (8/9).
• Many studies did not utilize current estrous synchronization protocols or insemination doses.

Conclusions:

• Double cervical AI timed with estrus detection is effective for improving sheep pregnancy rates.
• Double FTAI requires further investigation, particularly with frozen-thawed semen and optimized hormonal protocols.
• Future research should focus on aligning FTAI methods with current best practices in sheep reproduction.