Recent development in freezing strategies of pig semen-A review

Of late studies on frozen thawed boar semen have dramatically improved boar semen cryopreservation technique, albeit the commercial application of cryopreserved boar semen has not yet been popular. Some studies claimed successful fertility/ fertilization with frozen boar semen. Multiple researches are being carried out to evolve a suitable freezing protocol for cryopreservation of boar semen. In general, freezing protocol adopts freezing rates of either 20°, 40° or 60°C/min in lactose egg yolk extender with 2–3% glycerol using medium straw (0.5 ml) for freezing of boar semen. The supplementation of vitamin E or its analogues Trolox, butylated hydroxytoluene, reduced glutathione, catalase, superoxide dismutase, ascorbic acid, and alpha-lipoic acid to the freezing media of boar semen increase the cryosurvival of frozen-thawed boar spermatozoa. Treating sperm with cholesterol-loaded methyl-β-cyclodextrin increases sperm cryosurvival rates and sperm quality after thawing by partly decreasing membrane damage induced during phase transition from fluid to the crystalline-gel state. High fertility rates with cooled, frozen-thawed or sex-sorted boar semen are feasible to achieve by using appropriate insemination procedures. Post-cervical intra-uterine insemination allowed a three-fold reduction of spermatozoa to be inseminated, whereas deep uterine insemination allowed a substantial reduction in the number of cooled (5–20 folds) or frozen-thawed (6-folds) spermatozoa. With combination of different approaches, acceptable fertility with cryopreserved boar semen can be achieved facilitating its use in routine and commercial application. This review depicts best ways possible to adopt suitable freezing strategies for cryopreservation of boar semen.