update on semen cryopreservation in sheep and goats: a review

Despite the long history of artificial insemination, its widespread use in many species, including the poultry, sheep, and goat, has been faced with many challenges especially when frozen semen is used. the freezingthawing process results in physical and chemical insults on the sperm which subsequently decrease the fertility of the sperm. the decrease in fertility is much greater in most species compared with the species such as cattle. many factors affect the fertility of the frozenthawed sperm, and different procedures, including the use of various extenders, have been investigated to improve the quality of frozenthawed sperm. glycerol and egg yolk are traditionally used as the protective components in many extenders. despite the positive effects of the egg yolk (mainly as a result of its lowdensity lipoproteins), there have been concerns with the use of animal products in semen extenders. therefore, attempts have been made to substitute the egg yolk with other sources such as lecithin. there are reports that several additives such as disaccharides, antioxidants, and essential oils may have beneficial effects on the fertility of frozenthawed sperm. variable success rates were reported, and a small number of publications contained fertility data. in this paper, i shall review the most recent research findings on frozenthawed sperm in sheep and goats, supplemented with data on other mammals when appropriate.