Does Evaluation of One or Two Ejaculates of Rooster Semen Provide a Valid Basis for Culling Inferior Males?

Despite the practice of spiking flocks with younger males, reproductive problems increasingly impact the capability of flock managers to produce needed chicks and increase the cost of chick production. The problem also impacts breeders and producers using artificial insemination (AI). Recognizing that the problem is partially caused by poor semen quality, flock managers might consider evaluation of young males and culling those whose semen is of low quality. This logically leads to two questions. What should be evaluated and how many ejaculates should be evaluated before deciding to cull a rooster or tom? Important semen attributes include volume and number of sperm per milliliter (concentration) plus attributes of sperm function such as motion, exclusion of vital dyes, capability to bind to the oviduct epithelium, or capability to bind to the perivitelline membrane of an ovum. Herein, we focus on general aspects of gathering valid information on semen rather than what to measure, although roosters producing few sperm should be culled. Such a focus is to provide flock supervisors a rational basis to make decisions based on limited data. To estimate predictive value, we used available data for three successive ejaculates from each of 114 broiler roosters in a pedigree flock. Data collected were number of sperm per milliliter of semen and capability of sperm to bind in an in vitro sperm-binding assay. The average for all three ejaculates was used to identify those roosters in the lowest 20% for each trait. For both tests, the odds of making the correct culling decision based on one ejaculate was less than 2:1 (erroneous conclusion was made >35% of time). For the binding assay, but not sperm concentration, evaluation of two successive ejaculates increased the odds of a correct decision to greater than 3:1. When assessing these traits, we recommend evaluation of three successive ejaculates to enable a flock supervisor to usually, with reasonable reliability, make correct decisions to cull or not cull a rooster.