Effect of somatotropin on changes in milk production and composition during coliform mastitis in periparturient cows.
The potential protective and therapeutic effects of bST during coliform mastitis in periparturient cows were evaluated. In a first study, 19 cows, classified as moderate or severe responders based on the respiratory burst activity of blood neutrophils, were treated with recombinant bST or vehicle 48 h after intramammary inoculation of Escherichia coli. Clinical status and changes in milk production and composition were compared in the four groups. In a second study, 8 cows received bST or vehicle 7 d before bacterial challenge. During mastitis, losses in milk production and compositional changes were most pronounced in infected glands and in severe responders. Milk production of bST cows recovered better than that of placebo cows. Recovery of milk components was accelerated in severe responders treated with bST, but not in moderate responders. Pretreatment of severe responders with bST enhanced milk production before infection, protected the mammary glands from excessive loss of milk during the subsequently induced coliform mastitis, and accelerated normalization of milk composition. In conclusion, the beneficial effects of bST upon normalization of milk production and composition in periparturient cows suffering from coliform mastitis seem to be restricted to the severe responders. In severe responders that had been treated with bST, changes observed during mastitis resembled those in moderate responders treated with the placebo.