Evaluation of fertility: biological basis and practical application

Fertility in poultry is generally measured as the "percentage fertile eggs" laid by hens during a period of time following artificial insemination or natural mating. This parameter has presented some problems for the statisti cal analysis of fertility and its main limitations derive from the binary c lassification of an egg as fertile or infertile. An alternative measurement of breeding efficiency is the number of spermatozoa that associate with eg gs at fertilisation. These can be estimated in laid eggs and present a robu st and fundamental measurement of the efficiency of sperm transfer into hen s. In several applications they have revealed differences in the efficiency of mating or artificial insemination that were not discernible by traditio nal estimations of fertility.