Genetic variability in milking speed of dairy goats

The present investigation deals with the genetic variability of milking spe ed, measured as the volume of milk collected during the first minute of mil king (MD1), and its association with dairy traits. Data originated from 258 9 lactations of 1421 Alpine goats, sired by 93 bucks, measured between 1985 and 1997 at the Moissac Goat Experimental Station (Lozere, France). Two ge netic analyses were carried out. Firstly, a polygenic model was used to est imate genetic and phenotypic parameters among milking speed and dairy trait s using a multiple-trait animal model. Secondly, segregation analysis was u sed to test the hypothesis of mixed model inheritance (polygenes + major ge ne) for MF1. Heritability and repeatability of MF1 under the polygenic mode l were high (0.65 and 0.82, respectively). Estimated genetic and phenotypic correlations between milking speed and dairy traits were low, positive for yields and negative for contents. Segregation analysis yielded a highly si gnificant likelihood ratio, confirming the segregation of a major gene with two alleles with partial dominance. The difference between the mean values of the two homozygotes was around 2.3 phenotypic standard deviation units of the trait. The major gene explained more than 60 % of the estimated tota l genetic variance. The estimate of the 'residual' heritability, after taki ng into account the effect of the major locus, was 0.30.