RESPONSES OF DAIRY-COWS SUPPLEMENTED WITH SOMATOTROPIN DURING WEEK-5 THROUGH WEEK-43 OF LACTATION

Beginning at wk 5 of lactation, 136 cows (34 per treatment) were suppl emented daily for 38 wk with 0, 10.3, 20.6, or 41.2 mg of recombinantl y derived bST monomer. Cows were obtained from University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio Sta te University. Nine cows(4 at 0 mg/d, 1 at 10.3 mg/d, 1 at 20.6 mg/d, and 3 at 41.2 mg/d) did not complete the experiment because of health problems. Data from these cows were included in the reproduction and h ealth databases but not in the production database. Cows supplemented with bST produced more milk, consumed more feed, had lower rates of BW gain, and had improved efficiencies of milk production (conversion of feed and NE(L) to milk). Additional increases in productivity were mo dest at 20.6 and 41.2 mg/d versus productivity at 10.3 mg/d of bST. Co ncentrations of fat, protein, and TS in milk were unaffected. At 10.3 mg/d, bST did not adversely affect reproduction or health.