Production performance of dairy cattle administered recombinantly derived bovine somatotropin (USAN, Somavubove) daily: a dose range study.

Herds (n = 9) were used on which cattle (n = 598) received 0, 4.3, 8.6, 12.9 or 17.2 mg of recombinant bovine somatotropin (rbST; USAN, Somavubove) daily from about 75 d postpartum until lactation end. Minimum effective dose to increase (3.5% fat corrected milk) FCM of cows (multiparous) compared with controls is 2.0 mg rbST/d and maximum is 16.6 mg/d. Minimum effective dose to increase FCM of heifers (primiparous) is 5.0 mg rbST/d while the maximum is 16.7 mg/d. Dosing of 4.3 to 13.2 mg rbST/d enhances efficiency of FCM production in cows. Milk fat, protein, calcium and phosphorus were not effected by rbST except for instances of transient changes. Lactose was greatest in heifers given 12.9 mg rbST/d. Days of lost milk, incidents of mastitis, and somatic cell counts were not affected by rbST. Cows given 12.9 or 17.2 mg of rbST had reduced pregnancy and conception rates, whereas heifers did not. Total services, first service conception rate, services per conception, days open and days to first AI (artificial insemination) were not affected by rbST. Days between AI were greater in cows given 17.2 mg rbST/d. Restoration of body weight and condition occurred at slower rates in rbST-dosed cows. Heifers given 8.6 or 12.9 mg rbST/d gained more weight than controls. Net energy and protein balance was reduced (less so in heifers) near start of rbST but recovered as intakes increased. Cattle given rbST produce more milk than controls and should be managed accordingly.