Bovine Somatotropin

About[]

Bovine somatotropin, also known as bovine growth hormone, is a hormone in cows, produced in small quantities by the pituitary gland. It is a peptide hormone, meaning it targets the endocrine section, specifically the metabolic process. In short, it regulates, growth, development, and more. In this case it most importantly monitors milk production. A recombinant form of bovine somatotropin is primarily injected into dairy cattle in order to increase milk production. This is because at around day 70 of lactation, milk

production begins to decrease. This is mostly due to a decrease in milk-producing cells in the udder that do not regenerate until the following lactation period. Bovine somatotropin aids to counteract this decrease. If administered carefully, this protein halts the decrease of mammary cells and increases the number of nutrients directed toward them. This results in a prolonged peak of a lactation period. These effects are controlled by the insulin-like growth factor system, which is also mediated in response to bovine somatotropin administration in healthy cows (1).

Method

Choosing an expression system for producing large amounts of this recombinant protein depends on many

different factors including expression levels, cell growth characteristics, post-translational changes, and more (2). Therefore, bovine growth hormone, a single, non-glycosylated polypeptide chain containing 191 amino acids, is most commonly recombinantly expressed in Escherichia coli cells since they are quick reproducers, however it has also been been successfully expressed in other bacteria and yeast cells. The primers, derived from bovine blood samples through lysis of pituitary cells, code for the bovine somatotropin gene and are constructed based on its sequence, being DQ184480. Strains of E. Coli are used to carry the sequence, inserted through restriction enzyme sites NdeI and BamHI (3). Purification then takes place in order to make the protein injectable. This happens through isolation from inclusion bodies. The inclusion bodies are dissolved, refolded, and oxidized in urea, thus releasing the protein and rendering it "safe" for injection.

Controversy

While injection of recombinant bovine growth hormone is allowed in some countries such as the United States, Russia, and Brazil, many have banned the protein, including Canada, Australia, Japan, and more. This is for many different reasons. A European report on recombinant bovine somatotropin claims that usage of the protein can cause "severe and unnecessary pain, suffering, and distress" in cows, as well as mastitis, foot disorders, and various reproductive problems (1). The FDA claims that milk treated with this hormone is harmless, being nearly identical to untreated milk. However, slightly elevated levels of bovine somatotropin and Insulin-like growth factor 1 have many people weary of the effects. One study suggests that slightly raised levels of bovine somatotropin and Insulin-like growth factor 1 in rats caused them to develop thyroid cysts and infiltration of cells into the prostate. Another recent study shows a correlation between elevated amounts Insulin-like growth factor 1 in the blood and prostate cancer. These are only a few reasons why many people choose to boycott the synthetic protein (4).