Variation in the milk yield, endocrine and metabolic responses following bovine somatotropin administration to dairy cows

Extract

It is well established that the subcutaneous administration of bovine somatotropin (bst) to dairy cows results in an increased level of milk production. This effect occurs irrespective of the method of application, the duration of the treatment or the time after calving after which it commences. However, the reported extent of this galactopoietic effect in the published literature has been highly variable, with one long term study reporting an increase of over 11.5 kg/day (Bauman et al. 1985), whilst other long term studies have reported relatively small increases or no significant increase at all (Hof et al. 1991, Morbeck et al. 1991). As yet it is unknown what factors control the milk yield response to bst, though there is a clear effect of dose of the hormone and possibly of energy and protein balance. There are also confusing reports on the effect of the previous milk yield and genetic potential of the animal on the observed increase.