Abstract
Data from 51 107 and 11 839 ejaculates collected on rams of the "Lacaune" and "Manech tête rousse" breeds, respectively, were analysed to determine environmental and genetic factors affecting semen production traits (ejaculate volume, semen concentration, number of spermatozoa and motility) in young (≤1 year) and adult (≥2 years) rams. Fixed effects and variance components were estimated using multiple trait animal models within each breed. For all traits, the main environmental effects identified were year, season, number of ejaculations, daily variation, interval from previous to current collection and age. Heritability estimates were moderate for volume, concentration and number of spermatozoa (0.12 to 0.33) and lower for motility (0.02 to 0.14). Genetic correlations between ages differed from 1 for all traits (0.14 to 0.90), indicating that semen characteristics corresponded to different traits in young and adult rams. Genetic and phenotypic correlations among traits within age category were globally similar for the different breeds and categories of animals.
Highlights
In the ovine species, more than 800 000 artificial inseminations (AI) are performed each year in France with fresh semen
A wide range of genetic parameter estimates of semen traits have been reported in the literature but limited data are available for sheep [7, 22]
The maximal variations due to the main fixed effects reaching significance for at least one trait are presented in Tables II and III for Manech tête rousse” (MTR) and LAC rams, respectively
Summary
More than 800 000 artificial inseminations (AI) are performed each year in France with fresh semen. For a given preservation technique, the number of doses produced per ejaculate depends on the volume, sperm concentration and sperm motility. These traits are affected by environmental, management, physiological status and genetic effects. The principal environmental effects reported in the literature are the age of the ram, season or photoperiodic treatment, nutrition, rhythm of collection, collector and daily period [2, 4, 6, 8, 12, 15, 17, 21,22,23]. A wide range of genetic parameter estimates of semen traits have been reported in the literature but limited data are available for sheep [7, 22]
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