Cryoprotectants used in buck semen preservation: A review

Goat production is gradually changing from low input extensive system to agri-business model under semi-intensive and intensive systems on commercial production. Accordingly, semen freezing and artificial insemination (AI) is gaining demand among stakeholders in goat husbandry. The composition of buck semen diluent and freezing protocol have been standardized over the years and the research results revealed wide variation in post-thaw seminal traits. This review discusses in detail about various cryoprotective agents (CPAs), their classification, their level, various combinations used in buck semen freezing and also recent advances in cryoprotectants for improving post-thaw recovery of buck sperm. Among different cryoprotectants, 6% glycerol as permeable and 10% egg yolk as non-permeable CPAs yielded satisfactory post-thaw sperm motility (> 40%) with functional quality for successful fertility. The alternative CPAs viz., dimethyl sulfoxide (DMSO), ethylene glycol and dimethyl formamide yielded 13.80 to 21.78%, 12.86 to 31.79% and 13.40 to 18.10% post-thaw motility, respectively. However, the combination of glycerol + DMSO and glycerol + propylene glycol yielded 26.2 to 60.0% post-thaw motility. The use of universally accepted glycerol (6%) and egg yolk (10%) in buck semen preservation is sufficient in liquid and frozen buck semen for AI. However, it is necessary to standardise the levels and temperature of commonly used CPAs breed-wise for higher post-thaw recovery and fertility.