GENETIC-CHARACTERISTICS AND EVOLUTION OF SEMEN PRODUCTION OF YOUNG NORMANDE BULLS

Genetic parameters on average volume of the ejaculate, spermatozoa concentration, motility score and percentage of motile spermatozoa after thawing were estimated by restricted maximum likelihood applied to an animal model and using records collected from 1957 young Normande bulls. The heritability of the average volume of the ejaculate is very high (h2 = 0.65 +/- 0.09). Sperm quality traits are moderately heritable (h2 = 0.23 +/- 0.08 for motility score to 0.37 +/- 0.09 for concentration) and strongly correlated. Total percentage of abnormal spermatozoa estimated from a selected subset seems less heritable (h2 = 0.19 +/- 0.07). A Best Linear Unbiased Prediction was then carried out on the records from 2387 bulls using these estimates. No clear genetic trend could be detected in the population, although the phenotypic selection performed should be efficient. This apparent contradiction results from the increasing influence in the breed of one family of heavily used bull sires with a poor genetic merit on sperm production traits.