Growth Hormones June 25, 2008 9:08 pm
Posted by Bret in Uncategorized.Tags: beef, cow, growth hormone, milk
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In response to Janelle’s question: “Have there been any significant changes to farm animals’ biology and behavior in the last few decades due to the increased use of growth hormones? Could our interference actually change or speed up their evolution as a species?”
Hormonal therapy has become an integral part of large animal veterinary medicine and livestock production. We use reproductive hormones to manipulate the estrus cycle of females to increase breeding efficiency, give hormones to animals to alter growth and development (largely for economic benefit) and remove naturally occurring hormones from animal to alter behavior and reproductive potential (spaying and neutering animals). So first some background information on growth hormones used in the animal industry:
Growth hormones have one basic principle, to increase production of an economically desirable commodity. Usually this is in the form of meat or milk. We’ll talk about these separately. First, to increase carcass yield from meat animals you must begin with an animal that has the potential to grow to your desired specifications, basically the genetic capability to grow, gain weight and convert feed to muscle mass. Hormonal additives are typically in the form of ear implants composed of estrogens, progesterones, synthetic anabolic steroids or a combination thereof. Estrogen and progesterone stimulate a natural release of growth hormone (GH) in higher levels than would naturally occur. This engages a cascade of metabolic processes that lower overall catabolism and increase the retention of amino acids by the animal’s body, thus leading to a significant gain in muscle mass over the animals life. Anabolic steroids are typically only used just prior to slaughter (if at all) for a short period of time as they create rapid growth but can sacrifice the quality of the meat if overused. So, growth hormone itself is not given, but rather other naturally occurring hormones are used to stimulate to animals body to produce its own GH.
When it comes to using hormonal therapy in increasing milk production the concept is similar. Recombinant bovine somatotropic hormone (rbST) has been widely publicized recently, especially in California where the dairy industry is huge. It is given to cows when they achieve peak lactation, typically about 10-12 weeks post-calving. It is a naturally occurring growth hormone that re-directs the use of absorbed nutrients to increase the milk yield over the course of an entire lactation. The cow does not produce more milk that she would naturally produce in a day at her peak lactation, but rather maintains that peak lactation for a longer period of time, thus increasing yield over the course of a lactation period (about 10 months). The cow isn’t over-milked or worn out as is often perceived, and no studies to this point have shown an increase in mastitis (udder infection) or other health issues.
These hormone supplements are perfectly safe for use and have all been approved by the FDA. When it comes to meat animal “enhancement” the animals receiving the treatment are not going to be used for breeding (and are usually steers or spayed heifers) and thus the effects are terminal and not propagated in the species. If these hormones are given to breeding animals they will usually have deleterious effects on reproductive capability and thus prevent any changes from entering the future gene pool. This is similar to men using anabolic steroids and having reduced testicular capacity due to negative feedback on hormonal regulation. rbST in dairy cows also does not alter the genetics of the cow or her offspring but may make it more difficult for that particular cow to be re-bred with the efficiency desired on large dairies (studies vary on conception rates in cows using rbST). They still breed back, it can just take longer under normal management practices.
Our interference with these additives is not altering the evolution of these species, but our breeding selections and genetic manipulations are certainly placing pressure on all species to change. This is nothing new and has been ongoing since humans first domesticated animals and sought out desired characteristics. I am not aware of any effects these additives have on behavior but I will look into it. I’m sure Dave will have something to say about the biotechnology and genetic modification of animals lately…
imemerson
tungtide
Bret
Interesting. Well, I’m glad to know that increasing milk yield is not adversely affecting cows and that additives are not altering the evolution.
I’m concerned about the consequences of selective breeding as our past experiments have been less than successful in my eyes. On one hand we have sterile mules and ligers, and seedless fruits. While perhaps useful, beautiful and convenient respectively, our interference seems incompatible with nature in that these species can only exist through human interference and not reproduce in their own right. On the other hand we have Persian cats with breathing problems, Bloodhounds with eye problems, and Dachshunds with spinal problems. Selective breeding has created new and/or specialized breeds of dogs, but is causing chronic health problems for the animals.
Oh and as a side note on “carcass yield”… YUCK!
Very interesting. Although I am sure that there have been studies that show these things are not harmful to the humans consuming the milk and meat of these treated animals, I have to wonder at how repeated long-term exposure will affect us.
Americans are growing larger (including me!), and everyone is attributing that to our lifestyle, but could the hormonal tampering with our food supply be contributing to that?
I wouldn’t think that animal hormones would have much of an effect on human growth for a few reasons:
1. Most hormones are proteins (rBST is a good example) and will not survive the digestive process intact.
2. Any hormones that do survive that process would still need to be absorbed in the intestines and pass through metabolism in the liver which would further break down the compounds. Non-protein hormones would also be subject to breakdown in the liver.
3. Hormones function by either binding to cell receptors or to Response Elements (REs) on DNA. Human receptors and REs will be structurally different than those in cows or any other animals. While there is some structural similarity, it is unlikely that exogenous (from outside the body) hormones will have an effect.
4. Even if the hormones have an effect on humans, the concentrations obtained from eating the meat would be low. Even accounting for increased levels due to rBST treatment I don’t imagine that there is enough present to have a physiological effect on human development.
SOG knives…
Interesting ideas… I wonder how the Hollywood media would portray this?…
I agree with Dave, in the fact that any supplemental hormone that may be ingested would not pose a threat to the human as it would be broken down into amino acids and metabolized. There is some on-going research I’ve been looking through that addresses this, though all of the following scenarios are THEORY ONLY and have not been scientifically proven. They are worth mentioning in this forum, though, because they are based on scientific principles.
FACT: While the growth hormone rBST (used to prolong the lactation curve in dairy cattle and thus increase total lactation milk yield) itself is not secreted into the milk (there are no known growth hormone receptors in the bovine udder), the hormone does slightly alter the milk’s composition. There is an increased level of casein in rBST-treated cows milk, and consequently more long-chain fatty acids. This makes the same volume of milk more calorie-dense (albeit not by much).
UNDECIDED: There is an argument that consuming this milk has lead to human girls entering puberty and cycling earlier than other girls. It has not been proven, but is possible due to a slightly faster growth rate and deposition of muscle and fatty tissue (due to increased nutrient content, the same way in which obese girls have been observed enter puberty at an earlier age). Increases in fatty tissue can lead to increased leptin secretion, a hormone that stimulates GNRH (Gonadotropin Releasing Hormone) and thus initiates the menstrual cycle. These girls are not obese, and milk does not cause obesity, but a similar prinicple applies. Again, this is merely a THEORY at this time.
FACT: Other research is exploring the effects of IGF-1 (insulin-like growth factor 1, a polypeptide hormone with effects on growth and development) on changes in tibia growth and reproduction in mice. UNDECIDED: There is no firm evidence as it pertains to humans as of yet, but rBST-treated cows may secrete more IGF-1 than non-treated cows. This will be something to monitor as more research is published.
This is all theory at this time with no hard evidence yet, but something to consider. The hormone itself is not posing a risk, however the indirect effects may. I still drink the milk, but it is a very controversial issue.