EFFECT OF BOVINE SOMATOTROPIN ADMINISTERED TO PERIPARTURIENT DAIRY-COWS ON THE INCIDENCE OF METABOLIC DISEASE

Thirty-eight dry, pregnant Jersey cows were assigned to diet and bST t reatment in a 2 x 2 factorial design. During the dry period, half of t he cows were fed a normal TMR (0.4% Ca; 0.3 to 0.4% P), and half of th e cows were fed a high Ca TMR (1.5 to 1.6% Ca; 0.4 to 0.7% P). The hig h Ca diets were designed to induce milk fever and were relatively cati onic (194 to 293 meq/kg) compared with the normal diets (-131 to 30 me q/kg). A standard dairy diet was fed to all cows postcalving. Cows rec eived subcutaneous injections of either an oil-based excipient or 500 mg of bST in an oil-based excipient every 14 d from 28 d before expect ed calving until approximately 14 d postcalving. Peripartal bST treatm ent decreased the incidence of clinical mastitis, did not affect incid ence of milk fever, and increased the duration, but not the incidence, of ketosis in mature Jersey cows. Blood data confirmed the clinical r esponses and indicated that treated cows mobilized more bone Ca than d id controls, as was evidenced by increased hydroxyproline concentratio ns. Treatment with bST did not affect blood concentrations of 1,25-dih ydroxyvitamin D, Ca, or Mg. High Ca diets increased the incidence of m ilk fever and downer cow syndrome compared with normal diets. The effe ct of bST on mastitis and milk production must be considered as prelim inary given the small size of the study. Although bST treatment increa sed Ca mobilization, the effect was insufficient to prevent milk fever in this model.