Induced lactation in prepubertal Holstein heifers

Lactation was hormonally induced in six prepuberal Holstein heifers by seve n daily injections of estrogen and progesterone and three injections of dex amethasone on d 18, 19, and 20, followed by twice daily hand milking beginn ing on d 21. Heifers were about 6 mo old and weighed 162 kg at the beginnin g of the experiment. Secretions were obtained from five of six of heifers, and twice daily milking continued for 75 d in three of five heifers. The vo lume of milk obtained on d 7 ranged from 32 to 500 ml and averaged 4.7, 4.1 , and 3.7% lactose, protein, and fat, respectively. In the first natural la ctation, milk yield and composition were nearly identical for controls and induced heifers. Serum cr-lactalbumin was increased in induced heifers afte r treatment with dexamethasone and was highest on d 10 after onset of milki ng. Our data suggest that sufficient secretions for extensive biochemical t esting can be obtained following hormonal induction of lactation in a major ity of prepubertal heifers. Moreover, hormonal induction of lactation had n o apparent effect on reproduction or first natural lactation. While it is u nlikely that hormonal induction of lactation in prepubertal heifers is prac tical from a dairy production viewpoint, the advent of biotechnology for pr oduction of therapeutic recombinant proteins in the mammary gland of transg enic livestock has made early detection of these transgenic proteins very d esirable. We conclude that induction of lactation in prepubertal heifers is a viable technique for testing the expression of mammary-linked gene const ructs in transgenic cattle.