Hormones in Milk: Facts and Information
Dr.Hamid Ragab Hamid
Meat Inspection Unit, ADFCA
It is not quite uncommon to read and see arising debates about the food we consume: is it safe or does it endanger our lives? These debates are frequently given attention to and propagated without any scientific or medical base. Recently in the United Arab Emirates arised a voice that calls for a ban against dairy products originating from U.S.A.(6) due to the use of POSILAC® ,a synthetic growth hormone used to increase milk yield in dairy cows. Hereunder the scientific facts about some of the milk-excreted hormones with a special emphasis on bovine somatotropin (bST) are reviewed.
Hormones in the milk
A normal cow’s milk contains naturally a number of hormones of both protein and steroid nature. These hormones are present in very low concentrations (5, 13, 14, 16, 19). The first (protein) hormones include prolactin (50µg/L of cow's milk) and gonadotropin release hormone (1-5 µg/L) (16) whereas the steroid hormones include estradiol (175 µg/L), estrone (30 µg/L), progesterone (10-30µg/L) and the glucocorticoids cortisone and corticosterone (0.2-0.6µg/L) (16).
In 1990, many scientists (7) concluded that the concentrations of hormones in cow’s milk are very low compared to the levels of normal human hormones. The authors reported that a serving of 8 ounce of milk contains about 29 ng of estrogen whereas the adult nonpregnant female produces 48x104ng of estrogen/day. Therefore the serving of 16 ounce of milk/day will provide only 0.012% of the quantity of estrogen normally produced by the nonpregnant female.
Bovine Somatotropin (bST)
Somatotropin is a protein hormone that is excreted by the pituitary gland of all mammals. It is a major regulator of growth and milk production in lactating dairy cows (18).The mechanism whereby it increases milk production is not yet known however there are many hypotheses which include:
- Increases the blood flow to the mammary gland thence the milk precursors.
- Increases the insulin –like growth factors, namely IGF-I which plays a role in increasing the number of mammary cells and/or the synthetic activity of the existing cells.
- Reduces lypogensis in the body tissues therefore more free fatty acids (FFA) will be available for either oxidation in most tissues or milk fat production by the mammary gland cells
- Nitrogen conservation hence lowered plasma urea and nitrogen.
Trace amounts of bST are normally present in milk of untreated cows. A concentration of 1-10ng/ml was reported(4,8,9,17,29,30).The concentration of the hormone in the milk of cows treated with synthetic bST was not more than that of untreated animals(4,8,9,17,29,30).Collier et al (1991) measured the IGF-I in the milk of cows treated with the synthetic bovine somatotropin POSILAC and in the milk of untreated cows. They found no significant difference between the two groups in the measured hormone (14) .Other workers (4,8,17) found that the concentrations of IGF-I in the milk of cows treated by rbST were lower than the levels reported in human milk.
Synthetic Bovine Somatotropin (rbST)
During the 1920th it was observed that administration of bST to lactating cows significantly increased their milk production. Commercially the process was not significant as it required the purification of the pituitaries of 25 cows to get enough bST for a day supplementation of a single cow (32) .In 1979 an American company coordinated a research using the recombinant DNA technology to develop synthetic bovine somsatotropin.The gene code of bST was identified and spliced into the genetic sequence of the bacterium E.coli K-12.The hormone ,bST was produced within the bacterium during its genetic multiplication under the controlled laboratory conditions .
Recombinant Bovine Somatotropine and the Cow
The physiological effects of bST treatment are the same as those seen in any high-producing cow. Nutrition, health programs, environment, and milking technique must be appropriate for the use of bST. On many farms, the management changes instituted by producers as they are preparing to use bST will probably cause a greater increase in milk production, efficiency, and profitability than actual use of bST. In the initial stages of use, producers will be encouraged to use bST on cows that have been in lactation for at least 100 days, are in good physical condition, pregnant, and are free from health problems such as mastitis or infertility.
Concern has been expressed regarding the effect of bST on reproduction. The optimum calving interval of 12-13 months may lengthen because bST can extend the time that cows efficiently produce milk. Dairy Herd Improvement Association (DHIA) records show that higher milk-producing herds have lower conception rates than lower producing herds (11). This negative effect on reproduction is seen in cows treated with bST and is associated with increased milk production. However, some people believe that a longer calving interval could benefit the health of bST- treated cows, since many health problems of dairy cows are associated with calving and rebreeding. The ability of a cow to reproduce is affected by her physical condition, nutrition, health, and level of milk production.
Few research studies have investigated the physiological effects of bST on the functioning of the ovaries and pituitary gland. Cows receiving dosages of bST far beyond what will be used in practice have shown an adverse effect on estrous activity (the time when an animal is capable of being bred). This effect is not seen when cows receive low to average dosages of bST. High dosages of bST are reported to increase the death rate of calf embryos, so starting a cow on bST during early pregnancy should probably be avoided (11). This effect is not seen at recommended dosages. The effect of bST on reproduction will have to be monitored closely in individual herds.
Several research studies have shown that bST is not associated with increased mammary infections (mastitis) (11). Other studies have shown an increase in mammary gland infections when bST is used, but the increase is what would be expected with increased production. Critics of bST purport that bST increases a cow’s risk of mastitis, thereby exposing milk drinkers to additional animal antibiotics used in treatment. However, an FDA advisory committee concluded that other factors (e.g., season, age of the cows) are more likely than bST to be associated with mastitis (27). Moreover, FDA has established safeguards to prevent unsafe levels of antibiotic residues from entering the milk supply (27). The length of a cow's gestation (pregnancy), calf birth weight, calf survival rate, and calf growth are not influenced by using the product. Some early reports indicated an increased incidence of twins, but later reports failed to confirm this.
Recombinant Bovine Somatotropine and Milk Composition
Milk composition from bST-treated cows has been thoroughly investigated (2). The characteristics of milk from bST-treated cows are within the normal range of variation of milk from untreated cows. During the first 28 days of treatment, milk fat increases and milk protein decreases slightly. After longer treatment, cows adjust their nutrient intake and the normal balance is re-established. An increase in non-protein nitrogen and whey protein and a decrease in casein have been observed after long-term bST administration. This difference is not always significant, and the effect on cheese yield would probably be minor, if any. One study showed a slight increase in unsaturated compared to saturated fat. The difference was small, but suggested a healthier product from bST treatment. No differences in free fatty acids have been observed. Cholesterol levels are in the range of normal milk composition. Insulin-like growth factor I increases by up to two-fold in milk from treated cows, but it is still well within the range for both bovine and human milk. No differences in flavor have been found.
The National Institute of Health has concluded that milk from bST-treated cows is essentially the same as from untreated cows, and there is no difference in safety of the products.
Recombinant Bovine Somatotropine and the Health of Humans
bST has been proven safe for human health. The FDA (in a critical review of more than 120 studies) (17), scientists from Washington University School of Medicine in St. Louis and Cornell University in Ithaca, NY (8), a National Institutes of Health Technology Assessment Panel (29), the Office of Technology Assessment (30), the American Council on Science and Health (1) , and a commentary in the journal, Pediatrics (20), along with regulatory agencies worldwide, have independently concluded that dairy foods from bST-treated cows are safe for human consumption.
There are several reasons why bST residues in milk, present either naturally or as a result of bST administration to cows, do not have any physiological effect on humans ingesting the milk (4, 8, 9, 17, 29, 30). bST is species-specific, which means that bST is biologically inactive in humans, even if injected (8, 9, 17, 20). Also, pasteurization destroys 90% of bST in milk (17, 29). Furthermore, any trace amounts of bST ingested in milk are broken down into inactive fragments (i.e., constituent amino acids) by enzymes in the gastrointestinal tract, just like any other protein (8, 17, 29).
FDA, FAO, WHO and bST
FDA is not authorized to require special labeling for milk from bST-treated cows. However, food companies that do not use milk from cows supplemented with bST can voluntarily label their products with this information. To help ensure that consumers are not misled, FDA issued interim guidelines on February 8, 1994, for the voluntary labeling of milk from cows that have not been treated with BST (12). According to these guidelines, labels for dairy foods can state that the foods come from "cows not treated with" the hormone. However, the label would also have to carry an accompanying statement such as "No significant difference has been shown between milk derived from rbst-treated and non-rbst treated cows" (12).
The FDA has reaffirmed its 1993 position that milk from cows treated with BST is safe for human consumption (26). Likewise, the Joint FAO/WHO Expert Committee on Food Additives reconfirmed its 1992 position on the safety of bST (23).
The fore review clearly guides us to the conclusion that dairy products resemble no risk to the humans with respect to bST concentrations. It demands no legal certification that all dairy products from the U.S.A. are rbST-free.
References and Literature Cited
1. American Council of Science and Health. (1990). BST=A Safe, More Plentiful Milk Supply. September 1990.
2. Barbano, David M. and Joanna M. Lynch (1989). "Milk from bST Treated Cows: Composition and Manufacturing Properties." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11,
3. Bauman, Dale E. (1989)."Biology of Bovine Somatotropin." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, p. 1-8.
4. Blayney, D. P. (1994). Milk and biotechnology: maintaining safe, adequate milk supplies. Food Rev. 17(2):27-31.
5. Campana, W. M., and C. R. Baumrucker (1995). Hormones and growth factors in bovine milk. In: Handbook of Milk Composition. R.G. Jensen (Ed.). New York: Academic Press, pp. 476-494.
6. Cattle Drug Prompts Call for U.S.Dairy Import Ban. A news report,Gulftoday Newspaper, 05/07/2006, Abu Dhabi, U.A.E.
7. Collins, S. S., K. E. Belk, H. R. Cross, and G. C. Smith (1989). The EEC ban against growth-promoting hormones. Nutr. Rev. 47: 238-246
8. Doughaday, W. H., and D. M. Barbano (1990). Bovine somatotropin supplementation of dairy cows. Is the milk safe? JAMA 264: 1003-1005
9. Etherton, T. D., P. M. Kris-Etherton, and E. W. Mills. (1993). Recombinant bovine and porcine somatotropin: safety and benefits of these biotechnologies. J. Am. Diet. Assoc. 93: 177-180
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11. Ferguson, James D., and Andrew Skidmore.(1989). "Bovine Somatotropin - Reproduction and Health." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, p. 57-66.
12. Food and Drug Administration. (1994). Interim guidance on the voluntary labeling of milk and milk products from cows that have not been treated with recombinant bovine somatotropin. Fed. Regist. 59(Feb 10): 6279-6280
13. Gyawu, P., and G. S. Pope (1983). Estrogens in milk. J. Steroid Biochem. 19: 877-882
14. Hagemeister, H., H. Sick, and C. A. Barth (1990). Nitrogen balance in the human and effects of milk constituents. In: Role of Milk Protein in Human Nutrition. Bull. Int. Dairy Federation 253: 3-18
15. HHS News. U.S. Department of Health and Human Services. Nov. 5, 1993.
16. Jenness, R. (1988). Composition of milk. In: Fundamentals of Dairy Chemistry. 3rd ed. N. P. Wong, R. Jenness, M. Kenney, and E.H. Marth (Eds.). New York: Van Nostrand Reinhold Co., p.19.
17. Juskevich, J. C., and C. G. Guyer (1990). Bovine growth hormone: human food safety evaluation. Science 249: 875- 884.
18. Kenney, J., and D. Fallert. Livestock hormones in the United States (1989). Nat. Food Rev. 12: 21-24
19. Koldovsky, O., and W. Thornburg (1987). Hormones in milk. J. Pediatr. Gastroenterol. Nutr. 6: 172-196
20. Kretchmer, N. (1991) .Why not have more milk? Pediatrics .88: 1056-1057.
21. McDermott, Keyron. Editorial, The Des Moines Register, Des Moines, Iowa, May 3, 1990.
22. Milligan, Robert A. (1989). "Profitability of bST Technology." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, p. 36-48.
23. Murphy, J. (1998).JECFA approves safety of bST; report forwarded to Codex. Food Chemical News 40(4): March 16, 1998.
24. Peel, C. J.; D. L. Hurd; K. S. Madsen; and G. de Kerchove. (1989).Monsanto Agricultural Company. In Proceedings, Monsanto Technical Symposium, Oct. 24, 1989. The Monsanto Company, St. Louis, Missouri.
25. Review of Bovine Somatotropin. FDA Veterinarian. March/April 1990, Vol. V, No. II.
26. Report on the Food and Drug Administration’s Review of the Safety of Recombinant Bovine Somatotropin (1998). www.fda.gov/cvm/fda/infores/other/RBRPTFNL.htm.
27. Ropp, K. L. (1994).New animal drug increases milk production. FDA Consumer , 28(4): 24-27,
28. Stanton, B. jF. and A. M. Novalovic. "The Impact of bST Technologies: The Pros and Cons." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, 1989. p. 142-148.
29. Technology Assessment Panel. NIH Technology Assessment Conference statement on bovine somatotropin. JAMA 265: 1423-1425, 1991. (Nutr. Rev. 49: 227-232, 1991).
30. U.S. Congress, Office of Technology Assessment, U.S. Dairy Industry at a Crossroad: Biotechnology and Policy Choices: Special Report. OTA-F-470. Washington, DC: Superintendent of Documents, U.S.Government Printing Office, May 1991.
31. Written by Nolan R. Hartwig, D.V.M. Iowa State University Extension Veterinarian, and Gjlenda D. Webber, Office of Biotechnology, Iowa State University
32. Young, F.G (1947).Experimental stimulation of (galactopoiesis) of lactation.Br.Med.Bull; 5:155.