Bovine somatotropin

Bovine somatotropin (bST), or bovine growth hormone (BGH), is a specific type of growth hormone that is primarily released by the anterior pituitary gland of cattle. In addition to regulating somatic growth, BGH also influences the amount of milk produced by a dairy cow. Recombinant bovine growth hormone (rBGH), also known as rBST is a synthetic version of BGH that is injected into a cow to artificially maintain her milk production.
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Bovine growth hormone n. A naturally occurring hormone of cattle that regulates growth and milk production. [more]Bovine somatotropin - Community and Resources

A growth hormone found in cattle and having variations in all mammals. Injecting bST into lactating cows can greatly increase their milk production.

Also called bovine growth hormone, bST is a naturally occurring protein that has been genetically engineered as a synthetic compound (now manufactured in large quantities and commercially available to farmers) that causes cows to increase the efficiency of milk production per unit of feed consumed. Its use has caused public controversy, and some states require retail dairy product labels to identify the use of synthetic bST.