A note on heritability for milk production in Holstein herds of Baja California

Data from 1979 to 1989 of 2 678 lactations of 1863 Holstein cows were analy zed through the Derivative-Free Restricted Maximum Likelihood procedure to determine the heritability of milk production in five herds located in the valley and coastal zones of Baja California State. The animal model include d the effects of zone, herd, services per conception, lactation number and calving year as fixed effects; the direct additive genetic effect of the an imals were also considered. All fixed effects were highly significant (P < 0.01). The average milk production was of 8 431 +/- 43.4 kg and the direct additive genetic variance for this same trait was 1 233 555 kg(2), with a h eritability of 0.31. These results suggest that the selection programmes co uld be of great usefulness for the Holstein herds of Baja California state.