Measuring sperm:egg interaction to assess breeding efficiency in chickens and turkeys

Systems used to measure fertility in poultry have themselves presented a major impediment to progress in maintaining or improving fertility. Generally, these systems have been time-consuming, quantitatively inadequate, or both. A simplistic illustration of the basis of the problem is that if six fertile eggs were laid by a turkey hen during 1 wk after insemination, then all we know is what happened to six sperm: they fertilized the eggs. If 100 million sperm were inseminated, then information on the other 999,999,994 is missing. A better approach for quantitating breeding efficiency is to estimate the numbers of sperm that interact with the egg in the infundibulum. These can be identified in laid eggs, as sperm in the outer perivitelline layer (OPVL sperm), or holes produced by sperm in the inner perivitelline layer (IPVL holes). Eggs can contain up to 250,000 OPVL sperm, so the scale improves on binary estimation of fertilization status. The number of spermatozoa interacting with the perivitelline layer is related to the artificial insemination (AI) dose, the number of oviducal sperm, and the probability of fertilization, not just for one egg, but for subsequent eggs laid by the same hen. Practical applications of sperm:egg interaction measurements include: replacement of fertility trials for evaluation of semen; general fertility evaluation; and monitoring breeding efficiency of commercial turkey and broiler breeders. Furthermore, studies of sperm transfer into eggs raise interesting questions about the efficiency of turkey hens' response to AI or mating frequency of broiler hens in commercial flocks.