Abstract

Recombinant bovine somatotropin(rbST) administration to dairy cows increases milk production and improves the efficiency of milk synthesis, though management factors have been identified as major source of variation in dairy cows responses. Milk nutrient density is unaffected by rbST supplementation and no significant differences in milk composition between cows treated and not treated. The magnitude of reproductive responses of dairy cows to rbST is variable where there exists an increase in days to first estrus and twinning rates, increases days-open and services per conception. The use of rBST may have significant welfare consequences since unnaturally high milk yield production exist. This is reflected in different forms, among these, challenge of maintaining body condition of cows treated with rBST at the end of lactation, relative risk of mastitis due to increased milk yield and an increased incidence of lameness in cows. Reproductive problems in dairy cows have become very common as consequence of using rBST's, resulting with large numbers of cows being culled. rBST is biologically inactive in humans and its residues in food products have no physiological effect, but its injection to cow results in an increase in quantities of IGF-I and becomes one of the leading suspects involved in the development and spread of cancers. There is also suspect of increased human risk for development of anti microbial resistance in exposure to milk antibiotic residues from the use of rbST caused mastitis. This could be managed by practices in use by the dairy industry. The use of rbST reduces the resource used and environmental impact per unit of milk production. That is why increased animal performance is suggested as one of the most effective mitigation strategies to decrease greenhouse gas (GHG) and ammonia (NH3) emissions from livestock production per unit of product produced.