Response of Brazilian Crossbred Cows to Varying Doses of Bovine Somatotropin

¹ Department of Animal Sciences, University of Arizona, Tucson 85721
² Monsanto Co., St. Louis, MO 63167
³ Escola Superior de Agricultura Luiz de Queiroz, Piracicaba, São Paulo 13.400, Brazil

The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 Bos indicus x Bos taurus and 18 B. indicus x B. taurus) in Brazil. Cows were randomly assigned to treatments within stage of lactation [stage 1 = 56 to 100 d in milk (DIM); stage 2 = 101 to 199 DIM] and breed groups ( vs. B. indicus blood). Treatments were 250 or 500 mg of bST administered every 14 d. Cows in the control group did not receive bST or a placebo. Treated cows received bST injected subcutaneously in the postscapular region, alternating between the left and right sides. The 26-wk experiment consisted of 2 wk of pretreatment and 24 wk of treatment. Cows were housed in an open lot with regulated access to pasture. Cows were milked twice daily and scored for body condition at 2-wk intervals. Compared with controls, milk yield increased equally (22%) for cows receiving 250 or 500 mg of bST. Milk yield response to bST was higher and persisted longer during stage 1 of lactation than during stage 2 of lactation. No difference in response to bST was noted between cows with or B. indicus blood. Cows treated with 500 mg of bST tended to have more mastitis, but no other adverse health effects were observed. The potential use of 250-mg doses of bST at 14-d intervals in crossbred cattle in Brazil and other subtropical regions throughout the world is suggested, particularly before about 220 DIM.

Key Words: bovine somatotropin • crossbred cows • Brazil

Submitted on November 25, 1996
Accepted on July 17, 1997