Genetic and environmental trends of milk production in a closed flock of Beetal goats.

Genetic and environmental trends in first lactation milk yield, first lactation length, milk yield per day of lactation, and milk yield per day of kidding interval were determined from records on 1101 nannies, progeny of 86 sires, and spread over 37 yr. Genetic progress was computed from the regression of production on time with adjustment for deviation from random mating according to age, breeding value of dam, culling, and maternal effects. Genetic trends were positive for milk yield and yield per day of lactation and were 1.05 and 1.02% of their respective flock averages. Genetic trends were negative for lactation length and yield per day of kidding interval and were 1.19 and .43% of their respective flock means.