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.
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. Cows that have had more than one calf show a greater increase in milk production than do first lactation heifers. 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.
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. Records show that higher milk-producing herds have lower conception rates than lower producing herds. 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.
ReplyDeleteSeveral research studies have shown that bST is not associated with increased mammary infections (mastitis). 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.
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.
ReplyDeleteStudies 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.
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