Concerning the use of rBST (also known as rBGH) in cows to stimulate milk production:
1) The European Commission has issued statements and reports opposing the use of this synthetic hormone in cows based on health effects in cows as well as potential hazards for humans consuming the resulting milk. One such report is the “Report on Public Health Aspects of the Use of Bovine Somatotropin,” issued March 15-16, 1999, is available from The European Commission—Food Safety, at http://ec.europa.eu/food/fs/sc/scv/out19_en.html. Summary findings in that report include the following concerns:
• rBGH is known to increase the level of circulating insulin growth factor-1 (IGF-1) in the target animal followed by increased excretion of IGF-1 in milk. This report found that application of rBGH increases the amount of excreted IGF-1 in milk by 25-70 percent in individual animals. Bovine milk may also contain truncated IGF-1, which was found to be even more potent than IGF-1 in the anabolic response when given subcutaneously to rats. IGF-1 has an effect on endocrine, paracrine and autocrine mechanisms. There have been some links associated between circulating IGF-1 levels and risk of breast and prostate cancer. The report noted a need to further evaluate the effects of IGF-1 and related proteins present in milk from rBGH treated cows to gut pathophysiology, particularly of infants, and to gut-associated cancers.
• Secondary risks associated with the use of rBGH in dairy cows are: potential changes in milk protein composition which might be linked to allergic reactions, and increased use of antimicrobial substances in the treatment of rBGH-related mastitis, which could lead to increased risk of residue formation in milk and to antibiotic-resistant bacteria.
2) Several scientific studies concerning IGF-1 and cancer risks:
• “Dietary Correlates of Plasma Insulin-Like Growth Factor 1…” by M.D. Holmes et al., Cancer Epid. Biomarkers Prev., 9/11/02.
• “Insulin-like Growth Factors and Breast Cancer Risk in Chinese Women,” by H.Yu et al., Cancer Epid. Biomarkers Prev., 8/1/02.
• “Plasma Insulin-like Growth Factor-1 and Prostate Cancer Risk…”, by June M. Chan, Science, 1/23/98.
• A large long-term study of more than 1,000 nurses concluded that the more conventional milk drunk, the greater the women’s levels of IGF-1.
3) Canada prohibits the use of rBGH in commercial milk production. See http://www.hc-sc.gc.ca/ahc-asc/media/nr-cp/1999/1999_03_e.html. On Jan. 14, 1999, Health Canada announced that it would not approve the bovine growth hormone rBST for sale in Canada, a decision based on more than nine years of comprehensive review of its effects on animal and human safety. Veterinary experts cited an increased risk of mastitis up to 25 percent, infertility by 18 percent, and lameness by up to 50 percent. Such risks lead to a 20-25 percent increased risk of such animals being culled from the herd.
A meta-analysis published in The Canadian Journal of Veterinary Research in 2003 reported a nearly 25% increase in the risk of clinical mastitis in cows treated with rBST due to increased milk production, a 40% reduction in fertility, and 55% increased risk of development lameness. Mastitis can be treated with antibiotics, which can impact the sale of milk.