Maturity, a heritable trait in Saanen French dairy goat
Résumé
Maturity can be defined as the ratio of first parity milk yield on third parity milk yield and can be, according to the literature, associated with poor longevity. As longevity has been declining for several years in French dairy goats, maturity seems to be interesting to investigate. The objective of this work was to estimate the phenotypic and genetic coefficient of variation of maturity, its heritability, and genetic correlations with milk yield at first, second and third parity in dairy goat, in order to evaluate the feasibility of a future selection on this trait. The data set consisted of 32,807 first parities, 19,215 second parities, 9,386 third parities, and 9,386 maturity phenotypes of Saanen dairy goats. 66,300 animals were in the pedigree. The model developed was a multi-trait model with four traits: maturity, milk yields at first, second and third parities. The heritability of maturity was moderate and equal to 0.12±0.02, suggesting that this trait could be selected. The genetic correlations with production were equal to 0.30±0.07, -0.17±0.08 and -0.40±0.07 for first, second and third parities respectively. The genetic correlations of milk yield between parities were close to those estimated in a previous study: 0.87±0.02 between first and second parity, 0.75±0.03 between first and third parity, and 0.95±0.02 for the correlation between second and third parity. These correlations show that the production capacity of the first and third parity is not the same and that there is variability captured by the maturity trait. The phenotypic coefficient of variation was higher for maturity than for milk yield: 0.26 for maturity, 0.19 for the first parity, 0.21 for the second parity and 0.23 for the third parity. The genetic coefficients of variation were close whatever the trait: 0.09 for maturity, 0.11 for first parity, 0.11 for second parity and 0.12 for third parity. The correlation between maturity EBVs and longevity EBVs of AI bucks with at least 15 offspring was equal to 0.4. This correlation makes this trait interesting for use as a predictor of longevity. A future study will implement different predictors of longevity to improve the accuracy of longevity.