Genetic and environmental factors affecting milk production from dairy goats

The objectives of this study were to evaluate the influence of environmental factors on milk production from dairy goats raised in the Brazilian Southeast and to estimate genetic parameters for this trait through least squares. The data originated from seven farms and three breeds (Alpine Brown, Saanen and Toggenburg). Milk yields obtained from 1,336 lactations were initially fitted to a diphasic function, whereby total milk production (TMP) was estimated. The overall mean and standard error for TMP were 635.31 +/- 39.75 kg. A significant year x kidding season interaction was observed. In all three kidding seasons a quadratic yearly trend of PLT was observed: it increased from 1986 until mid-1990, decreasing thereafter. Age of maximum PLT was estimated as 46.65 months. Alpine Brown was superior to Saanen in some farms, the opposite occurring in others, but both showed higher PLT values than Toggenburg. Estimated heritability and repeatability coefficients were 0.296 +/- 0.079 and 0.227 +/- 0.033, respectively. These results show low reliability due to the small number of observations or to inconsistent PLT estimates obtained through the biphasic function. Since PLT is a sex-limited trait, it is suggested the use of progeny tests as the most efficient selection method for bucks and artificial insemination for spreading the selected genetic material.