The Impact of Bovine Somatotropin (BST)
Stefl, Carrie Glibbery
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For decades, dairy farmers and dairy breeders have sought to improve the production efficiency (milk produced/dollar of cost) of the U.S. dairy industry. They have primarily achieved this by selecting superior animals as parents to generate offspring capable of producing milk more efficiently. The program of genetic selection of parents has been a major contributor to the substantial advance in milk production efficiency over the past thirty years. In 1954, the U.S. average production per cow was 5,600 pounds of milk. In 1984, the average had risen to 12,000 pounds of milk per cow. (1) This dramatic improvement in efficiency, predominantly through genetic selection, has helped the U.S. dairy industry to remain vigorous and competitive within world markets. According to the EEC Dairy Facts and Figures, the EEC average in 1984, after the milk quota system emerged, was 9,000 pounds of milk per cow. Researchers studying the physiology of dairy cows noted a positive correlation between the production efficiency of cows of various types and in various stages of lactation with the blood level of bovine somatotropin produced naturally by the cow. They discovered that during the early stages of lactation, when milk production is high and most efficient, dairy cows have higher levels of bovine somatotropin ( BST) in their blood than the same cows during late stages of lactation, when milk production is low and least efficient. It was also noted that beef cows and low milk producing dairy cows have lower levels of naturally occurring BST in their blood. This direct correlation between the high natural levels of BST and high milk production efficiency provide the scientific basis for the improvements realized through selective breeding of superior dairy stock. The idea of using additional bovine somatotropin to supplement the natural level in dairy cows, therefore, is a logical extension of the process that the dairy industry has practiced for decades. Yet, the introduction of an artificial bovine somatotropin, manufactured by biotechnology, has been the center of a heated controversy for the past decade.