title: Response of Brazilian crossbred cows to varying doses of bovine somatotropin.
abstract: The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 1/2 Bos indicus x 1/2 Bos taurus and 18 1/4 B. indicus x 3/4 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 (1/2 vs. 1/4 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 1/2 or 1/4 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.
authors.affiliation: Department of Animal Sciences, University of Arizona, Tucson 85721, USA.
authors.forename: C
authors.initials: C
authors.lastname: Fontes Júnior
authors.forename: V K
authors.initials: VK
authors.lastname: Meserole
authors.forename: W
authors.initials: W
authors.lastname: Mattos
authors.forename: R P
authors.initials: RP
authors.lastname: Barros
authors.forename: Z
authors.initials: Z
authors.lastname: Wu
authors.forename: J T
authors.initials: JT
authors.lastname: Huber
mesh_terms: D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000502:physiology*; D004734:Energy Metabolism; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage* / Q000494:pharmacology; D007774:Lactation / Q000187:drug effects*; D008414:Mastitis, Bovine / Q000453:epidemiology
chemical_list: D013006:Growth Hormone