This chapter describes the studies of bovine somatotropin (BST) and dairy cattle which addressed animal health and safety. In addition to the efficacy of BST and its ability to increase milk production in dairy cattle, concerns about animal health as a consequence of its use have been raised. Several of the milk production studies have noted the presence or absence of health effects of dairy cows treated with BST. In the BST trials which examined changes in insulin, insulin was found to be higher in BST-treated animals than in controls in some studies, while in other studies, blood insulin levels were similar between treatments. BST treatment has increased gut absorption of calcium, increased accumulation of calcium into bone and also disappearance or resorption of calcium from bone. If BST puts undue stresses on cows, one might assume that cows treated with BST would have a higher incidence of infectious diseases or depressed immune responses.