Somatotropina bovina para vacas de leite em lactaçao. 1. produçao e composiçao do leite

The objective of this research was to evaluate the effect of recombinant bovine somatotropin (BST) on production and composition of milk and body condition score. Two experiments (1a and 1b) were conducted with 12 cows in each. In experiment la, the animals were semi-confined, fed chopped elephantgrass and concentrate during the day (1kg concentrate for each 2.5 kg of milk produced) and taken to pasture at night. In experiment lb, the animals were maintained in individual stalls and fed 55 percent corn silage and 45 percent concentrate on a dry matter basis. Milk yield was measured daily and milk composition analyzed weekly. Twelve cows (six in each experiment) were injected with 500 mg BST every 14 days, beginning 35 days postpartum. Each cow received ten doses of bST. Body condition scores were evaluated monthly. Milk yield was analyzed in a completely randomized design in a factorial scheme 2 x 175 days (two treatments and 175 days of lactation) with six replicates. For milk composition a completely randomized design in a factorial scheme 2 x 10 (two treatments and ten periods of 14 days) with six replicates was used. Milk yield increased 3.38 and 7.18 percent with bST treatment in experiments 1a and 1b, respectively. Milk composition was not affected by bST treatment and the average body condition scores were higher and lower, respectively, for bST treated cows in experiments 1a and 1b. The results indicated that BST increased the milk yield without affecting its composition. (RA)