Is selection on semen characteristics needed ?

A.I. studs and selection programs are interested in the broad distribution of sires of high genetic merit. This is at least partly conditioned by the semen characteristics (sperm quality and volume of the ejaculates) of the bulls. However, when most bulls have a satisfactory production or when management can be optimized to ensure maximum output, selection on semen characteristics can be considered too costly. In the last two decades, 10 to 15% of young Normande bulls have been culled each year due to their poor sperm quality. This selection had virtually no impact on their semen production. Nevertheless, it was found that selection was practiced correctly and that the traits selected are heritable. These contradictory results can be explained by the unfavorable influence in the breed of some heavily used sires of bulls with a poor genetic merit on sperm production traits. If the objective is to avoid a significant degradation of semen quality, one may conclude that a careful monitoring of the bull population is required. A proper genetic evaluation using all the information available (BLUP-animal model) must be implemented routinely. Then, efficient selection can be practiced if needed, at least within the families with the most unfavorable genetic characteristics.