Bovine somatotropin: review of an emerging animal technology

One of the first potential biotechnology products for animal production is bST. Research in the technology of bST has involved scientists and support from federal agencies, universities, and private industry. As a consequence of this extensive cooperation, more than 1000 bST studies have been conducted, which involved over 20,000 dairy cows, and results have been confirmed by scientists throughout the world. This quantity of published research is unprecedented for a new technology and greater than most dairy technologies in use. In contrast to steroids, bST is a protein hormone. Milk yield and persistency responses to bST have been observed for all dairy breeds examined. Quality of management is the major factor affecting magnitude of milk response to bST. The mechanism of action of bST involves a series of orchestrated changes in the metabolism of body tissues so that more nutrients can be used for milk synthesis. It is these coordinated changes that allow the animal to achieve an increased milk yield while remaining normal and healthy. Bioenergetic studies demonstrated that bST-supplemented animals are not stressed. Similarly, there are no adverse health effects from bST even under poor management conditions. Composition of milk (fat, protein, lactose, cholesterol, minerals, and vitamins) is not substantially altered when bST is used and does not differ in manufacturing characteristics. Public perception is of paramount importance if bST or any new technology is to be effectively implemented. New technology must be understood and perceived as safe and beneficial both by farmers, who would utilize it, and consumers, who would purchase the dairy products. With bST use, a unit of milk is produced with less feed and protein supplement and with a reduction in animal excreta (manure, urine, and methane). Nationally, the use of bST simply reinforces, but does not fundamentally change, dairy industry trends of increased milk yield per cow, reduced number of cows, and declining dairy farm numbers. For individual farms, bST technology is size-neutral. However, poorly managed farms where animals are stressed, underfed, or sick are at an economic disadvantage because they will achieve negligible milk response to bST.