Sperm fitness assessment in poultry: Brief review of in vitro methods

In the poultry industry, every chick or poult produced has high economic value; therefore, selection of male breeders capable of transmitting desirable traits to their offspring has an important role in fertility and hatching success. Following either natural mating or artificial insemination, sperm must go through a sequence of steps to fertilize the egg: 1. Go from the site of deposition (vagina) to the Sperm Storage Tubules (SST); 2. Enter and stay inside the SST; 3. Reacquire motility; and 4. Bind to and penetrate the egg. To perform these tasks successfully, sperm must be alive, motile, and have structural integrity (membrane, glycocalyx, acrosome, and DNA). To evaluate sperm fitness, several in vitro tests can be performed; however, it is often necessary to combine several assays to have a more reliable fertility estimation, as each procedure evaluates specific and distinct sperm features. In this article, we briefly review in vitro tests that can be used to evaluate poultry sperm, associating them with each step for fertilization. The sperm-egg interaction assay using the inner perivitelline layer of chicken eggs is highlighted, since it is a single test that evaluates multiple sperm characteristics and is highly correlated with fertility.