Bovine somatotropin and lactation: from basic science to commercial application

Bovine somatotropin (bST) results in increased milk yield and an unpreceden ted improvement in efficiency. Beginning in the 1930s to present day, inves tigations have examined animal-related factors such as nutrition, bioenerge tics, metabolism, health and well being and consumer-related factors such a s milk quality, manufacturing characteristics, and product safety. Overall, bST is a homeorhetic control involved in orchestrating many physiological processes. Direct effects involve adaptations in many tissues and the metab olism of all nutrient classes-carbohydrates, lipids, protein, and minerals. Mechanisms include alterations in key enzymes, intracellular signal transd uction systems, and tissue response to homeostatic signals. Indirect effect s involve the mammary gland and are thought to be mediated by the insulin-l ike growth factor (IGF) system. Specific changes include increased cellular rates of milk synthesis and enhanced maintenance of secretory cells. Indir ect effects are modulated by environment and management factors, especially nutritional status. This,modulation is a central component in allowing ST to play a key role in regulating nutrient utilization across a range of phy siological situations. U.S. commercial use began in 1994, and adoption has been extensive. From a consumer perspective, bST was unique, and special in terest groups loudly predicted dire consequences. However, introduction of bST had no impact on milk consumption, and milk labeled as recombinant bST- free occupies a minor niche market. From a producer perspective, commercial use verified scientific studies and enhanced net farm income. Overall, ST is a key homeorhetic control regulating nutrient partitioning, and the ST/I GF system plays a key role in animal performance and well being across a ra nge of physiological situations. (C) 1999 Elsevier Science Inc. All rights reserved.