Bovine somatotropin (bST) Bovine somatotropin (bST) is a metabolic protein hormone used to increase milk production in dairy cows. It was approved for commercial use in the U.S by the Food and Drug Administration (FDA) on November 5, 1993.
The following is a report on bST from the Biotechnology Information Series from Iowa State University. The Biotechnology Information Series may also be viewed in Acrobat PDF format by clicking here (
http://www.extension.iastate.edu/Pages/pubs/bi.htm).
BOVINE SOMATOTROPIN (bST)
December, 1993
Biotechnology Information Series (Bio-3)
North Central Regional Extension Publication
Iowa State University - University Extension
What is Bovine Somatotropin (bST)?
Bovine somatotropin is a growth hormone found in cattle. The word bovine refers to cattle, and the word somatotropin refers to the name of the hormone. Hormones are chemicals that are secreted by glands within the body. They are natural substances that affect the way the body operates. Bovine somatotropin, abbreviated as bST, is a protein hormone produced in cattle by the pituitary gland located at the base of the animals brain.
A hormone similar to bST is produced in all species of animals. This hormone is important for growth, development, and other bodily functions of all animals. In the 1930s, it was discovered that injecting bST into lactating (milk-producing) cows significantly increased milk production.
How Did Scientists Develop bST?
Until recently, the only source of bST was from the pituitary glands of slaughtered cattle. There were only small quantities of bST available, and it was very expensive.
Now, the new science of biotechnology makes it possible to work with DNA, the part of a cell that contains the genetic information for an animal or a plant. Scientists have determined which gene in cattle controls or codes for the production of bST. They have removed this gene from cattle and inserted it into a bacterium called Escherichia coli. This bacterium, which is found in the intestinal tract of humans and animals, acts like a tiny factory and produces large amounts of bST in controlled laboratory conditions. The bST produced by the bacteria is purified and then injected into cattle (figure 1)
http://www.biotech.iastate.edu/biotech_ ... _fig_1.jpg Figure 1. bST Production The movement of a gene from one organism to another, in this case from the pituitary gland of a cow to a bacterial organism, is called recombinant DNA technology. Several Food and Drug Administration (FDA) approved drugs, including insulin for the treatment of diabetes and tissue plasminogen activator (TPA) for the treatment of heart attacks in people, are produced in a similar way.
How Does bST Affect Milk Production?
To affect a cows milk production, bST must be injected into the animal on a regular basis, similar to the way insulin must be regularly injected into people who have certain types of diabetes. Feeding bST to cows will not work. Amino acids and peptides are the building blocks of proteins.
The hormone bST is a complex protein that is immediately broken down into small, inactive amino acids and peptides and rendered ineffective when it enters a cows digestive system. How often a cow must be injected with bST will depend on whether a bST product can be developed that releases the hormone gradually over a long period of time.
Milk yields are significantly increased when cows are injected with bST, although not as much as some reports in popular newspapers and magazines suggest. The exact details of how bST increases milk production are not known, but it is thought that blood flow to the cows mammary (milk-producing) gland is increased. The blood carries an increased amount of nutrients available for milk production. More nutrients are extracted from the blood by the mammary gland, which improves efficiency of milk production. Feed efficiency (pounds of milk produced per pound of feed consumed) is improved because more milk is produced and the proportion of feed used for body maintenance is decreased. The actual amount of feed consumed by bST-treated cows increases, helping the cow meet the increased nutrient demands.
Milk production in bST-treated cows increases from 4.8 to 11.2 pounds per day. Feed efficiency improves from 2.7 to 9.3 percent (Peel, et al.). Table 1 (
http://www.biotech.iastate.edu/biotech_ ... tml#Table1) summarizes the results of 32-week treatments of cows injected with bST in several states and foreign countries.
Misinformation provided by some groups gives the impression that there is controversy about the biology of somatotropin. However, 800 reports on 20,000 treated cows have yielded remarkably consistent results worldwide (Bauman).
Researchers have summarized several bST trials and found a milk production increase of 8.4 pounds per day (Bauman). They estimated that, depending on how the dairy operation is managed, average increased milk production is expected to range from 8.5 to 17.6 percent.
It is difficult to predict how individual cows will respond to bST. A higher response is seen when treatment is started after the cow has been producing milk for 101 days, rather than when treatment is started on days 57-100 after calving. The response o f cows treated in early lactation is less (Bauman). Cows that have had more than one calf show a greater increase in milk production than do first lactation heifers (Peel, et al.). Milk yield gradually increases for the first few days after bST treatment begins. A maximum increase is seen in about six days. To meet the needs for this increased milk production, treated cows consume from 10 to 20 percent more grain and forage.
Normally, cows reach their peak milk production 7-9 weeks after lactation begins. Milk quantity then slowly declines throughout the remainder of lactation. The ability of cows to maintain relatively high levels of milk production throughout lactation is called "persistency." The major response of cows treated with bST is a significant improvement in persistency. The normal decrease in milk yield as lactation progresses is markedly reduced. Quality of management, including health programs, milking pra ctices, nutrition, cow condition, and environmental conditions will be major factors in the response to bST.
What Are the Benefits and Risks of bST?
The commercial use of bST in dairy cattle is controversial and has stirred heated debate among the dairy industy, activist groups, and consumers.
Effects on cow health
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 or results will be disappointing. 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 (Ferguson and Skidmore). 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 (Ferguson and Skidmore). 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) (Ferguson and Skidmore). 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. The length of a cowUs 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.
Milk composition and safety
Consumer advocates and others have expressed concern about the safety of milk from bST-treated cows. All milk contains natural bST that is produced by the cow. Milk from bST-treated cows also contains the same amounts of injected bST and no differences can be measured compared to untreated cows. There are four forms of natural bST, and each has a chain of either 190 or 191 amino acids. The recombinant bST that is injected into cows has 191 amino acids. The biological activity of commercial bST is identical to naturally produced bST.
Studies indicate that both natural bST produced by the cow and bST produced by recombinant DNA techniques are immediately broken down into inactive amino acids and peptides in the digestive tract when they are consumed by humans. In contrast, steroid hormones such as estrogens, progesterones, and anabolic steroids are smaller, ring-like structures that are absorbed from the digestive tract and are biologically active in humans. This is not the case with bST in milk, whether it is produced naturally by the cow or by recombinant DNA technology (Barbano and Lynch).
Studies show that bovine somatotropin is inactive in humans. During the 1950s, natural bST produced by cows was injected into children with growth defects in an attempt to encourage growth. There was no effect, probably because the bovine somatotropin protein molecule differs from human somatotropin (human growth hormone) by about 30 percent of the amino acid sequences.
Milk composition from bST-treated cows has been thoroughly investigated (Barbano and Lynch). 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 aft er 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.
Economics
The potential economic effect of bST on the family dairy farm has generated heated debate. The Animal Health Institute, an organization of drug and vaccine manufacturers, maintains that the use of bST will be of equal value to any size farm (Milligan). They contend that use of the product will favor the good dairy manager, regardless of farm size.
Estimates of the effect of bST on dairy production have probably been exaggerated. The United States Department of Agriculture estimates that the use of bST could lead to a 2 to 5 percent increase in national milk production within five years, or about the increase seen yearly without the use of bST. This increase would be in addition to the normal milk production increase per cow.
In most dairy herds, bST will not be used in cows until they have been in lactation for about 100 days. It will not be used in cows with chronic health or fertility problems. It is expected that bST will be used less in heifers than in adult cows. If 50 percent of farmers adopt the use of bST, and it is used in 60 percent of the lactation days per user herd, milk production will increase about 3.5 percent (assuming an average per cow production increase of 15 percent). Many well-managed dairy herds increase per cow production more than this on an annual basis by using improved management and genetics. For most herds, a farmer who requests a thorough herd analysis by a competent nutritionist and veterinarian and then follows their recommendations will achieve a larger increase in milk production than by using bST alone.
Failure to adopt proven technology is a problem throughout the dairy industry. Almost 60 percent of cows are bred by mating to a bull, rather than by artificial insemination from proven sires with superior genetic performance. Only 50 percent of U.S. dairy producers use DHIA management information and records to improve production.
The government milk price support system tends to make prediction of the effect of bST on milk prices difficult. It is true, however, that efficient managers in areas of the country with higher milk prices benefit more from application of technology and increased production.
It is argued that large commercial dairy operations can begin using new technologies such as bST more easily, rapidly, and efficiently than smaller operations. Sophisticated record keeping and division of labor may make timely injection of cows with bST more feasible for these larger operations. Other demands on the time and management skills of typical Midwest dairy producers who have diversified farming operations may make new technology more difficult to implement.
Others argue that smaller producers with direct owner control of the herd can manage individual cows better and will see a greater production increase from the use of bST. It is not automatically true that larger herds are better managed and, therefore, will benefit more from bST.
There is no question that consumer loss of confidence in the quality of milk produced by using bST, whether the reasons are logical or not, would reduce milk consumption and have a negative economic impact on the dairy industry. This is a major concern of dairy producers. Relative to milk quality, bST appears to be neutral. It neither improves nor harms quality. Consumers would gain with bST technology since milk production costs may decline due to improved efficiency. The ultimate effect of use of bST on consumption is unknown.
How is bST Regulated?
The United States Food and Drug Administration (FDA) is responsible for regulating the use of bST since it is an animal drug and because milk and meat are food products. Several commercial companies have submitted data to the FDA, asking for approval to use bST in dairy cows to increase milk production.
Before approval of bST for use in dairy herds, the FDA allowed the consumption of milk and meat from animals that received bST as part of the experimental testing process. Such approval is often granted during the process of license approval of animal products. Milk from treated cows has been judged safe because bST is biologically inactive in humans and is a protein hormone that is digested and destroyed by gastric enzymes when it is consumed. Each company seeking approval for bST has to demonstrate that bST has zero biological activity in milk when it is consumed. The FDA has found no pertinent information indicating that food derived from bST-treated cows is unsafe. (Review). It is not required that producers withhold milk from the market for a certain period of time after test herd cows have been treated with bST.
Federal law prohibits the social and economic effects of a product from affecting the FDA's decision whether to approve its use or not. The FDA must determine if a product is safe, pure, potent, and effective. Producers can decide whether a product is economical or useful. Approval by the FDA does not mean that a product must be used, but only that it can be used, if desired.
Testing required by the FDA
Before any new product can be approved, companies must demonstrate its effectiveness under actual use conditions in several geographic locations. Fifty cows per herd are required for bST approval. Three dosages of bST were used for the studies submitted to the FDA. The quality control of bST used in the test herds was monitored and all procedures to be used were approved by the FDA before the testing began. The majority of the tests in the approval process were performed by independent scientists at university laboratories and farms or in commercial herds.
Cows were injected with bST at various times during the lactation period. The effectiveness of the drug and its safety for the first and later lactation periods were monitored. Milk yield was calculated on a 3.5 percent fat basis. Milk composition, including fat, crude protein, lactose, calcium, and phosphorus, were measured about once per week. Daily feed intake was measured in the test herds. Body condition and health were monitored throughout the studies. The effect of bST treatment on reproducti on was evaluated, including breeding cycles, conception rates, number of breedings per conception, length of time from calving to the next conception, abortions, incidence of twins, calving difficulties, and stillbirths. The weight, growth, and health of calves during the first four weeks of life were monitored. Monthly somatic cell counts, as a measure of mastitis, were required. The sites where bST was injected were monitored for any signs of adverse reactions.
To evaluate safety, companies had to use one, three, and five times the expected dosage level of bST for two consecutive lactations in one of their test herds. Heifers born to treated cows were raised through breeding age and monitored for abnormalities. Companies seeking approval for bST were also required to prove that its use was not harmful to the environment.
First bST product approval granted by FDA
On November 5, 1993, the FDA announced approval of a bST product, the animal drug sometribove, for increasing milk production in dairy cows. The Monsanto Company of St. Louis, Missouri, developed the drug. However, the drug could not be used immediately due to a 90-day moratorium imposed by Congress during the summer of 1993. The moratorium was designed to give the White House Office of Management and Budget time to study possible consumer reaction and the drug's impact on the dairy industry.
The FDA approval also carried with it some provisions to deal with antibiotic residue concerns. In September 1992, the General Accounting Office reported that the FDA had found evidence in submitted clinical trials that bST-treated cows have a slightly increased incidence of mastitis. This report raised concerns that antibiotic treatments for mastitis could lead to increased antibiotic residues in milk. States require milk to be tested for drug residues. Milk found to have unsafe levels of residues must be discarded.
Although an FDA advisory committee concluded in March 1993 that adequate safeguards exist to prevent unsafe levels of antibiotic residues from entering the milk supply, additional steps were taken to ensure that any unsafe residues in the milk of bST-treated cows are detected before the milk or its products are marketed.
According to a news release issued by the U.S. Department of Health and Human Services (HHS News), Monsanto agreed to a post-approval monitoring program that includes:
A two-year tracking system of milk production and drug residues in 21 top dairy states that will periodically compare the amount of milk discarded after bST is marketed to the amount discarded prior to approval.
A 12-month comparison of the proportion of milk discarded due to positive drug tests between bST-treated and untreated herds.
A reporting system to monitor all bST use and follow up on all complaints.
The use of sometribove in 24 commercial dairy herds will be specifically monitored for mastitis, animal drug use, and the resulting loss of milk.
The FDA has concluded that it has no legal basis to require special labeling of food products derived from bST-treated cows. Food companies may voluntarily label their products, provided the information is truthful and not misleading to consumers.
What are the Controversies Concerning the Use of bST?
The most intense controversy surrounding approval of bST for use in dairy cows has occurred in major dairy producing states in the Great Lakes and New England areas. Representatives of the dairy industry are concerned about the ultimate economic effect on producers.
Consumer and environmental advocacy groups have expressed opposition based on concerns about milk quality and the use of biotechnology in general.
Dairy producers
Some producers are afraid that they will not be able to keep up with new technologies and they will suffer economically as a result. Others feel that a product such as bST will work to the disadvantage of producers in the Great Lakes States and the Northeast. Natural resistance to new technology adoption and a fear of genetic engineering techniques cause some producers to resist the approval and use of bST.
Special interest groups
Activist groups with a variety of agendas and motives have addressed the bST issue. Some have stated that milk from treated cows may not be safe after all, and more testing is needed. Others see this as a scare tactic to delay or block the use of bST and undermine consumer confidence in milk from bST-treated cows. Some animal rights groups see the use of animals for food, under any circumstances, as inhumane or a violation of those animals' "rights".S Others have stated that cows have a right not to be injected with bST.
Others
Other opposing arguments state that the FDA does no independent testing of its own, but only monitors the studies of the companies seeking approval. The persistent oversupply of milk and dairy products has also been cited as a reason to block the use of bST. Some dairy farmers oppose the use of bST but feel they would have no choice but to use the product in their own herd in order to stay competitive if bST came into general use (McDermott).
Table 2 (
http://www.biotech.iastate.edu/biotech_ ... tml#Table2) summarizes arguments for and against the use of bST in the categories of food safety and its effect on the number and size of farms.
What Lies Ahead?
Use of bST will have a significant effect on the research and development investment in agricultural biotechnology by commercial firms. Universities will be expected to provide unbiased scientific information.
Patience, tolerance, and understanding will be required by educators, extension workers, and other professionals in agriculture who work with groups that either support or oppose implementation of technology such as bST.
Table 1. Increases in milk production and feed efficiency of bST-treated cows (Peel, et al.)
Location
Increase in Milk Yield (%)
Increase in Feed Efficiency (%)
Arizona
8.3
2.7
Cornell University
11.5
5.3
Missouri/Monsanto
21.8
8.2
Utah/Utah State U.
14.6
5.3
France
17.8
9.3
Germany
16.6
4.9
Netherlands
18.5
7.1
United Kingdom
19.2
5.4
Table 2. Arguments for and against the use of bST (Stanton and Novalovic)
Food Safety
Arguments for use of bST:
Arguments against use:
1. Safety is not an issue; bST is naturally present in milk and would be broken down in the digestive process.
1. Can we really be sure that milk from bST-treated cows is safe? Do we really know we need to know?
2. The FDA approval process can be trusted.
2. The FDA is understaffed and over-worked. Their credibility is not high.
3. Consumers will be reassured when they get the complete story of safety of milk from treated cows.
3. We won't see lower milk prices. Retail food prices increase even when farm prices decline.
4. Improved efficiency of production will reduce prices to consumers.
4. Dairy product consumption at best will be unaffected, and more likely will be hurt by approval of bST.
5. Milk consumption will increase when prices decline.
5. Scientists donUt really know what sells dairy products.
6. Decreased prices will be an advantage for low income families.
6. Organizations will work hard to convince consumers that bST is bad.
7. Some consumers will prefer RorganicS (non-bST-treated) milk. Marketers could sell such an RorganicS product.
7. Moratoria imposed by some states will make consumers more wary.
8. Consumers wonUt believe the chemical companies and FDA when they refute negative campaigns.
9. The dairy industry canUt afford to stake everything on what some people say is scientific truth.
Effects on Number and Size of Farms
Arguments for use:
Arguments against use:
1. bST is size neutral.
1. Economies of scale work against the small producer.
2. Careful management may give an advantage to small farms.
2. Increased feed and forage for bST-treated cows is more difficult to produce on smaller farms.
3. Those who implement bST effectively soon after approval will have an advantage.
3. Small farms will be pushed out faster. Farm buildings and other assets will be worth less as more producers are forced out of dairy production.
4. Small farms can handle this technology.
4. There will be a period of oversupply of milk.
5. Farm size has been increasing and number of dairy farms has been decreasing for years. This will occur with or without approval of bST.
5. In the Northeast and Midwest, fewer farms will result in decreased service and supplier support for remaining farms.
6. bST will give smaller farms a chance to improve performance.
6. bST is one more thing to buy, one more risk to take.
7. Increased manure production will slow bST use on large farms.
7. Uncertainty increases risk. This works to the disadvantage of small farms.
8. bST will assist farmers who are low cost producers, regardless of farm or herd size.
8. The financial spread between small and large farms will get wider.
9. There is an adverse effect on the environment and quality of life when large farms are favored.
For More Information
Dairy News and Information Center, 2233 Wisconsin Avenue, N.W., Suite 500, Washington, D. C. 20007. Tel. toll-free 1-800-343-2479.
Nolan R. Hartwig, D.V.M. Extension Veterinarian, 2270E Veterinary Medicine Complex, Iowa State University, Ames, Iowa 50011. Tel. (515) 294-8790.
Agricultural Biotechnology: Issues and Choices. Copyright 1991 by Purdue Research Foundation. Available from Agricultural Communication Service, Media Distribution Center, Purdue University, West Lafayette, Indiana 47907.
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References
Barbano, David M. and Joanna M. Lynch. "Milk from bST Treated Cows: Composition and Manufacturing Properties." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, 1989.
Bauman, Dale E. "Biology of Bovine Somatotropin." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, 1989. p. 1-8.
Ferguson, James D., and Andrew Skidmore. "Bovine Somatotropin -Reproduction and Health." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, 1989. p. 57-66.
HHS News. U.S. Department of Health and Human Services. Nov. 5, 1993.
McDermott, Keyron. Editorial, The Des Moines Register, Des Moines, Iowa, May 3, 1990.
Milligan, Robert A. "Profitability of bST Technology." Advanced Technologies Facing the Dairy Industry: bST. Cornell University. Nov. 10-11, 1989. p. 36-48.
Peel, C. J.; D. L. Hurd; K. S. Madsen; and G. de Kerchove. Monsanto Agricultural Company. In Proceedings, Monsanto Technical Symposium, Oct. 24, 1989. The Monsanto Company, St. Louis, Missouri.
Review of Bovine Somatotropin. FDA Veterinarian. March/April 1990, Vol. V, No. II.
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.
Written by Nolan R. Hartwig, D.V.M. Iowa State University Extension Veterinarian, and Gjlenda D. Webber, Office of Biotechnology, Iowa State University.
