In lactating dairy cattle, bovine somatotropin (bST) is a naturally occurring species-specific protein hormone and major regulator of milk production. It is produced in the brain and coordinates metabolism to allow more nutrients for milk production. Recombinant bovine somatotropin (rbST) is a synthetic version of bST which is primarily injected into dairy cattle to increase their milk production. Since the 1970’s it has been synthesized in the lab and, in 1993, approved by the FDA as safe for use and for commercial sale. rbST works by increasing milk production in lactating cows and is administrated during week 9 – 10 of the natural lactation cycle (peak) and continued every two weeks until the end of lactation. rbST increases the efficiency of nutrient utilization by keeping milk producing cells alive and active longer, resulting in higher lactation persistency and therefore, a higher milk yield.

bST or rbST is metabolized in the liver, where Insulin-like Growth Factor-1 (IGF-1) is released and circulated to milk duct tissues. IGF-1 is a secondary hormone produced by mammals in response to levels of natural growth hormones (bST) and coordinates cellular growth and function. The addition of rbST stimulates more production of IGF-1, which circulates to milk duct tissues. The molecular structure of bovine IGF-1 and human IGF is identical and the amounts of IGF-1 in cows treated with rbST are within the normal range of that found in untreated cows. According to the FDA, rbST is orally inactive in humans and therefore should not have any physiological effect on the human body from consumption of milk.

There is no scientifically proven, FDA-approved test for cows’ milk to determine whether the cows have received rbST supplementation. The lack of a test is not surprising because there are no differences in the composition of the milk — neither the macro-components nor the micro-components. Consumer confidence in food tests is maintained knowing that FDA requires rigorous proof before certifying the validity of such tests.

Milk is a nutritious food, and its composition does not differ whether it is labelled as conventional, rbST free or organic. Milk and dairy products labelled as rbST-free or organic are niche products marketed by producers following a particular management system. There is no FDA-approved test that can differentiate between milk from rbST-supplemented and unsupplemented cows. If properly handled, all milk, regardless of the production system, is natural, pure, and safe.

Bovine somatotropin causes no changes in milk composition of any practical importance to consumers. The minor differences in milk composition shown between unsupplemented and bST-supplemented cows are well within normal biological variation in milk composition. All cows produce bST and all milk contains bST. The use of rbST has no significant effect on the micro and macro composition of the milk and the flavour of the milk is unaffected. Natural variations occur due to factors such as genetics, diet, cow breed, age, lactation stage, environment, season, and milking practices such as milking interval and frequency. However, these factors would have an equal effect in rbST supplemented and unsupplemented cows. The pH, macro- and micronutrient as well as somatic cell count of milk was unaffected by bST injections.

All food production has an environmental impact, but that of dairy production is reduced when milk yield per cow is increased. The use of rbST allows each cow to produce about 4.5kg of extra milk per day and the net effect of this is an 8-9% reduction in the carbon footprint per liter of milk. In simple terms, six cows injected with rbST is equal to 7 untreated cows. The use of rbST allows the milk supply to be produced with fewer total cows and feedstuffs. Therefore, an adequate milk supply can be achieved, requiring less land and water to raise crops, which in turn means a reduction in soil erosion and the use of herbicides and pesticides. Smaller herds also means less fossil fuel and electricity are required for operations, and the output of manure and animal waste is reduced. In summary, if we inject 50% of South Africa’s dairy herd (which is ± 275,000 cows), it equals the annual removal of 110,000 cars from the road or planting 82.5 million trees.

Voluntary feed intake increases in bST-supplemented dairy cows. This increase occurs after a few weeks of bST supplementation, persists throughout the interval of bST-use, and has been consistently observed across a wide range of diets. The magnitude of increase in feed intake is dependent on the response in milk yield and the energy density of the diet. Overall, cows supplemented with bST adjust their voluntary intake in a predictable manner related to the extra nutrients required for increased production of milk. If cows are given an inadequate amount of feed or are fed a diet without adequate nutrient balance, then the magnitude of response to bST will decrease according to the extent of the inadequacy. A rule of thumb is that for every additional liter of milk that is produced, a cow will need 300g of extra feed.

Several factors affect the profitability of cows supplemented with rbST. Some of these costs include feed, labor, product price, milk price and achieved milk production response. The use of rbST to improve productivity within the lactating cow herd allows for a reduction in resource use and environmental impact per unit of milk. The use of bST increases milk yield and production efficiency. When cows produce more efficiently, they become more profitable. rbST increases lactation milk yield by altering the lactation curve. Not only does milk yield increase immediately upon rbST administration, but milk yield is maintained at a higher persistency throughout the lactation cycle compared to unsupplemented cows. Once the milk yield is increased without any other rising costs, the maintenance costs get diluted and thus increasing the profitability.

Quality of management is a major factor determining milk yield response, as is the quantity and quality of feed provided. Management quality will be the major factor affecting the magnitude of milk response to rbST. Facets that constitute the quality of the overall management program include the herd health program, milking practices, nutrition program, and environmental conditions. Management factors have been identified as a major source of variation to the response to rbST. The factors that have been identified are the dosage of rbST, injection intervals, genetic potential, and environmental conditions. Better managed dairy cows have a greater response to rbST than poorly managed dairy cows. The factors that influence milk production have been identified in response to rbST research trials: herd management quality including the availability, quantity and quality of feed bST dosage age of the cow body condition of the cow prior to starting rbST-supplementation health of the cow before and during the treatment.

Milk contains trace levels of bST, less than one part per billion, but there is no difference in bST levels in milk from rbST-supplemented and unsupplemented cows. Protein hormones are broken down to amino acids in the digestive processes and are then absorbed by the gastrointestinal tract. Milk also contains trace levels of other hormones but their concentration range does not differ between milk from rbST-supplemented and unsupplemented cows. A cow’s blood levels of IGF-1 are elevated in rbST-supplemented cows even though milk concentrations do not differ from the IGF-1 range observed in milk from unsupplemented cows. Because the biological effects of IGF-1 are not species-specific, as they are for rbST, when bST is administered to dairy cows, the concentration of IGF-1 in blood increases about threefold and the levels of IGF-1 in milk can increase up to twofold. IGF-1 in milk does not pose a safety risk because it is a protein and is digested like all other dietary proteins.

A hormone can be described as a chemical transmitter substance secreted by humans, animals and plants that regulates physiological activities and maintains homeostasis. Hormones act as chemical messengers that travel throughout the body to organs, stimulating certain life processes and retarding others. Hormones are produced by various organs, glands, tissues, and cells endogenously throughout the lifecycle and can be an integral part of the structure of the human, animal or plant. Endocrine glands are specialized organs that secrete hormones into the endocrine-signaling system. Hormones can be steroids or proteins. Steroid hormones are active in the body when consumed orally. For example, birth control pills, vitamin D, testosterone. Protein hormones are broken down into amino acids by digestive processes which are then absorbed by the gastrointestinal tract. Therefore, ordinarily, protein hormones need to be injected into the body to have an effect. For example, insulin, oxytocin and bST.

Insuline-like growth factor-1 (IGF-1) is a secondary hormone produced by mammals in response to levels of natural growth hormones. IGF-1 circulates in the blood of mammals, coordinating cellular growth and function. Added synthetic growth hormone’s presence stimulates more production of IGF-1, which circulates to the milk duct tissues. Insuline-like growth factors are known to be important mediators of many biological processes, including growth, lactation, production and health. Numerous studies have demonstrated that an increase in blood bST levels upregulates the production of IGF-1, as measured in both blood and milk. This increase in IGF-1 levels is the primary driver that enhances milk production.

rbST has been claimed to cause various adverse health effects including ketosis, fatty liver, chronic wasting, lameness, milk fever, mastitis, infertility and heat intolerance. However, the US Office of Technology Assessment (OTA) maintains that if metabolic disorders occurred they would most likely appear during the first few days of rbST use and that none of the claimed health effects have been observed in long- or short-term studies since the first studies in 1937, including in acute or chronic toxicity studies. There have been claims that rbST reduces resistance to infectious and contagious diseases in cows but “none of the hundreds of bST studies report lower milk yield or decreased productive efficiency, both of which are associated with disease in cows”. Instead, it is suggested that rbST may help maintain immunity from disease. Cows that are stressed produce milk less efficiently and use more energy as heat. “Nothing illustrates the normalcy of bST-supplemented cows as effectively as the persistent gains in milk yield and productive efficiency throughout the treatment period.” Major factors affecting the incidence of mastitis include milking management, herd health programs and milk yield. It is difficult to detect and evaluate whether mastitis increases in rbST-supplemented cows result from bST-use independent of milk yield. One study reports a moderate increase in mastitis in rbST-treated cows, however it is 4-9 times less than the effects due to other variables such as season, lactation stage, number of lactations per animal and herd-to-herd variations. Some reviews indicate that rbST treatments result in decreased pregnancy rates but no change in conception rates, however, as decreased pregnancy rates are typically associated with increased milk production, it was concluded that “effects of high milk yield on reproductive performance are the same whether or not the high yield was due to rbST-use.” In addition, the calving interval for optimum economic return may be substantially increased when bST is used because bST improves persistency of lactation.

Administration of bST to lactating dairy cows increases the yield and efficiency of milk production. In response to injection of the bST, milk secretion increases within a day and is maximized within a week. The increased milk yield is maintained if treatment is continued, but quickly returns to control levels when bST is discontinued. The effects of rbST use on cow performance and health were an important factor in the FDA’s evaluation that led to the approval of rbST for commercial use in the United States. Studies have continued to examine effects on cow health and well-being including effects on culling, veterinary costs, lameness, reproduction, and mastitis. These follow-up studies found an increase in milk production when rbST supplements are used but there were no differences in cow health, culling or longevity.

No evidence exist of increased human risk from exposure to milk antibiotic residues due to rbST-supplementation. Milk residues occur when milk is saved before antibiotics have fully cleared. Withdrawal periods differ between products and is determined through research by pharmaceutical companies as well as government approval. Antibiotics and dumped milk cost the producer money, so producers do not use antibiotics unless they are necessary to help the animal overcome an illness. Antibiotic labels include warnings to inform producers how long milk must be dumped from a treated animal before the milk is clear to put into the bulk tank, known as the withdrawal period.

Some have expressed concern about human health effects due to the potential increases in milk antibiotic residues resulting from alleged higher levels of mastitis in rbST-treated cows. Antibiotic residues in milk can cause allergic reactions in humans and lead to antibiotic resistance. Major factors affecting the incidence of mastitis include milking management, herd health programs and milk yield. On a per-unit milk basis, the increase of 0.1 cases per cow per year is about 4-9 times less than from other variables such as season, lactation stage, number of lactations per animal and herd-to-herd variations. However, state and federal regulatory bodies monitor milk supplies for drug residues and demand disposal of milk with levels above standards. The dairy industry tests every tanker truck load for antibiotics before processing so that even if any increase in antibiotic-use occurred, the milk will be dumped before it enters the marketplace. Moreover, dairy producers who experience an increase in mastitis would likely re-evaluate their use of bST.

Some reviews indicate that rbST-treatments result in decreased pregnancy rates but no change in conception rates, however, as decreased pregnancy rates are typically associated with increased milk production, it was concluded that “effects of high milk yield on reproductive performance are the same whether or not the high yield was due to rbST-use.” In addition, the calving interval for optimum economic return may be substantially increased when bST is used because bST improves persistency of lactation.

Cows that are stressed produce milk less efficiently and use more energy as heat. “Nothing illustrates the normalcy of bST-supplemented cows as effectively as the persistent gains in milk yield and productive efficiency throughout the treatment period.” Heat stress occurs when cows generate and absorb more heat than they can easily get rid of by respiration, sweating and air circulation. Cows suffering from heat stress have decreased dry matter intake, milk production and pregnancy rates and an increase in lameness, disease incidence, days open and death rates. The effects of heat stress can also lead to late gestation, shorter gestation periods, calves with lower birth weights, reduced milk production and impaired immune function. Increasing milk production will lead to an increase in body temperature of a cow. Supplementation of rbST increases cows’ milk production so heat stress will have a greater effect on higher producing cows. All animals are affected by heat stress and thus leads to a decrease in milk production but rbST-supplemented cows recover faster that unsupplemented cows. rbST-supplemented and unsupplemented cows that are higher producing will try and maintain their body heat as well as try to stay in homeostasis.

IGF-1 is a secondary hormone produced by mammals in response to levels of natural growth hormones (bST) and coordinates cellular growth and function. The addition of rbST stimulates more production of IGF-1, which circulates to milk duct tissues. The molecular structure of bovine IGF-1 and human IGF is identical and the amounts of IGF-1 in cows treated with rbST are within the normal range of that found in untreated cows. According to the FDA, rbST is orally inactive in humans and therefore, if consumed from food products such as milk, should have no physiological effect on the human body. In fact, there is no significant difference in bST levels in milk from rbST-treated and untreated cows. Even if there was, the human digestive system would break down and inactivate bST in the human body. In addition, bST does not affect human growth hormone receptors as bST is species-specific.

rbST has been claimed to cause various adverse health effects including ketosis, fatty liver, chronic wasting, lameness, milk fever, mastitis, infertility, and heat intolerance. However, the US Office of Technology Assessment (OTA) maintains that if metabolic disorders occurred they would most likely appear during the first few days of rbST use and that none of the claimed health effects have been observed in long- or short-term studies since the first studies in 1937, including in acute or chronic toxicity studies. There have been claims that rbST reduces resistance to infectious and contagious diseases in cows but “none of the hundreds of bST studies report lower milk yield or decreased productive efficiency, both of which are associated with disease in cows”. Instead, it is suggested that rbST may help maintain immunity from disease. Cows that are stressed produce milk less efficiently and use more energy as heat. “Nothing illustrates the normalcy of bST-supplemented cows as effectively as the persistent gains in milk yield and productive efficiency throughout the treatment period.” Major factors affecting the incidence of mastitis include milking management, herd health programs and milk yield. It is difficult to detect and evaluate whether mastitis increases in rbST-supplemented cows result from bST-use independent of milk yield. One study reports a moderate increase in mastitis in rbST-treated cows, however it is 4-9 times less than the effects due to other variables such as season, lactation stage, number of lactations per animal and herd-to-herd variations. Some reviews indicate that rbST treatments result in decreased pregnancy rates but no change in conception rates, however, as decreased pregnancy rates are typically associated with increased milk production, it was concluded that “effects of high milk yield on reproductive performance are the same whether or not the high yield was due to rbST-use.” In addition, the calving interval for optimum economic return may be substantially increased when bST is used because bST improves persistency of lactation.