Sheep Artificial Insemination: History, Current Practices, Limitations, and Methodological Challenges

Artificial insemination (AI) is a key reproductive biotechnology for genetic improvement in sheep. However, its efficiency remains lower and more variable than in most other livestock species. This review critically synthesizes the historical foundations of sheep AI, including methodological principles established by the Soviet school, and evaluates how these concepts have been further developed and adapted to contemporary reproductive biology. Particular emphasis is placed on estrous synchronization protocols, semen processing and cryopreservation, and insemination techniques. We highlight how anatomical constraints of the ovine cervix, seasonal reproductive physiology, and species-specific characteristics of ram sperm collectively limit fertility outcomes, especially when frozen–thawed semen is used. Comparative analysis of cervical, transcervical, and laparoscopic insemination methods indicates that laparoscopic AI remains the most reliable approach, although recent advances in catheter design and semen handling have improved the feasibility of less invasive techniques. This review further discusses emerging approaches, including sperm sex-sorting, alternative recovery methods, and early-stage spermatogonial stem cell–based technologies, emphasizing both their potential applications and current limitations. Overall, the available evidence suggests that future progress in sheep AI will depend on the integrated optimization of hormonal synchronization, semen preservation, and insemination strategies, rather than on isolated technical innovations.