Document Type : Invited Review
Department of Animal Science, College of Agriculture, Shiraz University, Shiraz, Iran.
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 freezing-thawing 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 frozen-thawed sperm, and different procedures, including the use of various extenders, have been investigated to improve the quality of frozen-thawed 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 low-density 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 frozen-thawed 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 frozen-thawed sperm in sheep and goats, supplemented with data on other mammals when appropriate.