Although only one sperm is needed to fertilize an egg, the likelihood of getting fertile eggs increases when more sperm penetrate the yolk. In most cases many sperm penetrate the membrane surrounding the yolk. The perivitelline sperm hole assay is used to assess female fertility by counting the number of holes made by sperm attempting to fertilize an egg. A high number of sperm holes indicate high female fertility. Maintaining fertility in older hens is important because as age increases, fertility and hatchability decrease.
Older hens have less ability to effectively store sperm.
Past research has looked at improving fertility by adding selenium to male diets, but little work has been done using selenium to improve female fertility and egg quality. Recent research at the University of Alberta examined the effects of increasing the normal amount of selenium in layer diets by adding additional organic or inorganic selenium. This should improve fertility in older laying hens by increasing the length of time sperm can be stored. One group was fed a standard diet with selenium-supplementation from a normal premix. These diets were fed for 3 wk.