Factors affecting milk yield of Holstein cows hormonally induced to lactation

Abstract

Induction to lactation in cows subjected to growth hormone treatment in intensive conditions has not been studied. The aim of this study was to determine the environmental factors that affect the milk production variables of Holstein cows hormonally induced to lactation and treated with bovine somatotropin (bST) through lactation. To induce lactation 1,500 Holstein dairy cows (nulliparous and pluriparous) of a high milk potential were intensively managed. The cows were induced to lactation with daily subcutaneous administration of 50 mg d-1 of progesterone, and 2 d-1 mg of estradiol cypionate (days 1-7), from day 8 to 14, the cows received a daily injection of estradiol cypionate (2 mg d-1). From day 18 to 20 they were administered a daily injection of 0.5 mg flumethasone. 500 mg bST were applied on days 1, 6, 16 and 21, and milking started on day 21. After 60 days of lactation, all cows received somatotropin every 14 days throughout lactation. Milk production at 305 days during the winter was similar to the fall, but significantly higher (p<0.01) than the ones obtained in cows that began lactation in the spring and the summer. The range of lactation was from 200 to 1400 days of lactation. It was concluded that with the hormonally induced lactation and use of somatropin, it is possible to reach lactation of more than 1,000 days and that the continuation of lactation is plastic and can be modified (improved) through better nutrition after peak lactation and the increasing of the milking frequency, achieving lactations longer than two years, with milk yields over 20,000 kg of milk in most of the cows in this study.