Photorefractoriness is a condition that was exhibited in all fowl before modern selection programmes were implemented. Expressed in its absolute biological form, it ensures that birds cannot hatch and then breed in the same season. This paper reviews the literature regarding the exhibition of photorefractoriness, within populations and between genders, in avian species. Photorefractoriness has been eliminated in commercial laying hens, and the possibility of selecting against this in broiler breeders is investigated, as it would result in increased egg output and fertility, especially in operations in which it is not possible to rear these birds on short (<10 h) days.
