Antibiotics, hormones, and feed additives

Making feed better

Animals' biological systems know when they are lacking a nutrient and will naturally seek it out. Many of the mammoth fossil are found near mineral deposits, often referred to as 'salt or mineral licks'. These are places where high concentrations of salt and other minerals exist on the ground. The animals lick the ground to acquire minerals like sodium, iron, calcium, phosphorus, and zinc that they need but can't acquire from their normal food sources. Most all wild herbivores find the need to visit salt licks periodically. If they unable to find the minerals they need these animals will often engage in unusual eating behaviors, like the Red Deer at the Island of Rhum in Scotland who eat baby birds. This island is particularly low in calcium and phosphorus, so the deer acquire it by consuming the bones in the baby birds. Carnivores have less of a need for salt licks because these minerals are already present in the meat they consume. Understanding herbivores' need for minerals, farmers have provided them to their livestock since ancient times, as keeping them confined in fences prevents them from finding these minerals on their own.

Livestock farmers have long recognized their animals need a number of nutrients that are not always available in the grasses and grains fed to them. One reason farmers used to raise different types of livestock on the same farm was that it was necessary. Hogs would be be fed cooked bones, guts, meat, even the stomach contents of slaughtered beef. Both hogs and chickens were encouraged to consume hog manure, both to utilize what the cows did not digest and to acquire other nutrients not present in the grains they were fed. In particular, it was known that chickens and swine (or any single-stomach animal) benefitted greatly from the consumption of proteins found in other animals. Poultry would die if they were raised entirely indoors; there was some nutrient they acquired elsewhere that was not adequetely present in the grain they were fed.

Our understanding of animal nutrition improved dramatically when vitamins were discovered in the early twentieth century. Scientists soon discovered animals needed a variety of vitamins and trace minerals for good health, and so they started producing them and adding them to feed. Once Vitamin D was added to chicken feed farmers could now raised them entirely indoors. It was also discovered that animals were healthier and grew faster if given supplements of Vitamin B12.

During World War II there was a push to improve the feed efficiency of livestock. The benefits of supplementing Vitamin B12 were known but there were no cheap sources of the vitamins. Antibiotics had recently been discovered, and one company developed a way of making antibiotics in large tanks. They realized the waste from these tanks contained high levels of Vitamin B12. So they added this 'waste' as a supplement to animal feed and discovered it produced an enormous increase in animal weight gain. And it wasn't due to the vitamins alone, as the animals grew 50% faster on this supplement than they did more expensive forms of Vitamin B12. They eventually realized it was the antibiotics in the waste that caused the additional increase in growth rates. Thus began the use of regularly adding small amounts of antibiotics—amounts so small it would not help fight infection— to animal feeds to increase feed conversion and growth rates.

Adding antibiotics to feed improved growth rates of single-stomach animals (e.g., pigs, chickens) considerably, but not remarkable improvements for ruminants like cattle. The cattle industry thus sough some type of feed additive that would give them a productivity boost, so in 1954 they experimented with the hormone diethylstilbestrol (DES). This is a synthetic version of estrogen that was given to women to reduce miscarriages and could be produced cheaply from coal tar. Animal scientists discovered that adding DES to cattle feed improved growth rates considerably and became a standard cattle feed additive. However, once scientists discovered that the hormone was causing cancer in women who took it they banned its use in livestock. By then, however, scientists had discovered safer growth hormones to use.

Figure 1—The dosage, not the chemical, makes the poison

Does the adding of hormones and antibiotics to feed concern you? There are certainly reasons for concern. Used appropriately it can cause harm. Early experiments giving synthetic estrogen to roosters caused them to grow female feathers, and when those chicken heads were fed to minks the minks would become barren. Not using these feed additives simply because they could cause harm is unwise though, as everything is a poison if one consumes too much of it, and nothing is a poison if consumed at very low levels. The question is: can we add hormones, antibiotics, and other additives to livestock feed to produce food more efficiently without threatening human health? The answer is an unequivocable: yes.

Growth hormones

Fears of growth hormones

I once toured an unusual chicken farm in Tulsa, OK. They raised chickens outside in pastures and they raised goats and cattle without administering any growth hormones. Their niche was selling 'natural' meat to urban consumers, where 'natural' here means the animals lived outside and were given feed that did not contain any antibiotics or growth hormones.

We were chatting about the market for natural meats, and the owner was explaining why consumers are fearful of the conventional meat sold in most grocery stores. He said that human females are going into puberty at an earlier age than they used to, and this is because of the extra growth hormones in the beef people eat. Beef used to be safe, he asserted, but now that farmers administer extra growth hormones to cattle the meat is packed with hormones that alter the human body. I laughed because I thought he was joking, but quickly realized he was not. So I apologized and let him explain.

He was correct about girls going into puberty at an earlier age than before. In 1860 girls went into puberty at about 16.6 years of age, but by 2010 it had dropped to 10.5 years of age. However, and this is why I laughed, it is definitely not due to growth hormones in meat. First, onset of puberty declined from 16.6 years in 1860 to 14.6 years in 1920, before farmers ever administered growth hormones to cattle. Second, there isn't hardly any more hormones in the meat from animals adiminstered growth hormones. Third, there is a much better explanation for the earlier onset of puberty: rising weights in children. Children who weigh more tend to go into puberty at an earier age. This is well known in Mauritania, where young girls are forced to consume large amounts of calories so that they can gain weight and begin puberty at an earlier age.

Video 1—Force feeding children in Mauritania to induce puberty

In this article I will argue that there are no dangers posed by the use of growth hormones in livestock production, so long as they are used according to government regulations. However, for many people the idea of is scary and they will oppose it no matter what the science says. Sometimes this is an irrational choice, sometimes it is because they believe the science is manipulated by unethical corporations and an ineffective regulatory system, in which case the fear can be rational. Imagine that the government started installing nuclear power stations across the US as a way to maintain energy production while lowering carbon emissions. Most all the major scientists and scientific organizations contend the new nuclear power stations are perfectly safe. Even if you are a strong supporter of science, is this enough for you to feel comfortable having a nuclear reactor down the road from your house? For many the answer is 'no', and some people feel the same way about growth hormones in livestock.

Use of growth hormones in beef production

All animals have growth hormones, as that is one mechanism by which the body determines whether to grow and how fast to grow. Most of the productivity improvements in agriculture has come from better genetic selection and improved feeds. When you select for animals that grow faster or produce more milk you are inherently selecting for animals that naturally produce more 'growth hormones', regardless of whether those hormones call for faster growth or more milk production.

Well, what if we, instead of selecting for genetics that produce more growth hormones, we simply give animals more growth hormones? Indeed, we regularly do such a thing in livestock production. Some of these hormones are the identical to the hormones the animal naturally produces, like estrogen, progesterone, and testosterone. Other times they are synthetic versions of the natural hormones. This means they are produced by humans, perhaps by genetically modifying a yeast to create the hormone. The synthetic growth hormones are either similar or identical to natural growth hormones produced by the animal. In the figure below you see that this hormone implant is designed specifically for heifers that will not be slaughtered until they are much older, and it contains both estrogen and testosterone.

Figure 2—Example of growth hormones used in beef cattle

Cattle may receive implants while they are nursing, as they enter the stocker phase, and/or as they enter the feedlot. They can increase growth in all three phases, but it is in the feedlot stage where hormone implants are used almost universally (unless the beef is to be marketed as hormone-free), at it is here it has the greatest impact. Is this a safe practice? All evidence says yes. There are strict regulations on how implants can be administered, and so long as these regulations are followed there is zero impact on food safety. To illustrate, consider the figure below. Yes, beef from cattle administered hormones will have higher levels of hormones than from cattle not given the hormones. However, that increase in hormone levels is miniscule compared to the overall levels found in normal foods. Simply put, hormone use in livestock agriculture is perfectly safe.

Figure 3—Hormone levels in beef from cattle given growth hormones

The FDA is not going to allow livestock producers to use hormones in a way that would jeopardize food safety. It will establish regulations such that the dosages adminstered to animals and the 'withdrawal time' (number of days between the time the hormones are administered and the animal is slaughtered) is such that no health harms are ever expected. Of course, if producers do not follow these regulations then food safety can be threatened, but this is true for many technologies in agriculture, like pesticide use.

Subtherapeutic antibiotic use

When animals develop a bacterial infection we obviously want to give them antibiotics at a level (referred to as a therapeutic level) that stops the infection and allows the animal to recover its health. However, as mentioned in the introduction, scientists have learned that all livestock grow faster and stay healthier if they are administered smaller dosages of antibiotics—referred to subtherapeutic levels—every day in the animals' feed or water. This lowers the cost, resource use, and carbon footprint of pork production. For this reason it is used in most all livestock industries, especially the beef, pork, and broiler industry. (Broilers are chickens raised for meat, as opposed to layers which are chickens raised for egg production. Antibiotics are rarely used in the egg industry.)

As you might expect, though, subtherapeutic antibiotic use does pose dangers, some of which are more real than others. If residues of the antibiotics remain in the meat and are consumed by someone allergic to them it could cause an allergic reaction. Of course, we know this, and so regulations require a proper withdrawal time to ensure there are zero traces of antibiotic residues in meat. So this is not a real problem.

Figure 4—Virtually all meat is free of antibiotic residues

The danger is that we feed so much antibiotics to livestock at such a low level that it encourages the development of antibiotic-resistant bacteria. Constantly exposing dangerous bacteria to small amounts of the antibiotics makes it easier for the bacteria to develop resistance—it's like target practice for the bacteria. Around 80% of all the antibiotics used in the US are added to animal feed. If such antibiotic-resistant bacteria develop, and if those bacteria infect humans, then we may not be able to cure those infections with antibiotics. How serious of a threat is this? That is a question of much debate.

  • There are logical reasons to believe subtherapeutic antibiotic use in livestock does not threaten human health. Roughly 75% of all antibiotics used on farms are used only infrequently or not at all by humans, so for human health to be threatened a bacteria has to (a) randomly develop resistance through mutation (b) it has to be resistant to one of the antibiotics that humans use (c) it has to be a bacteria species that infects humans (d) it has to somehow leave the farm and then has to infect humans. The probability of this happening is, to some, very low. Make no mistake, this absolutely can happen and probably already has. The question is how often it occurs.
  • Others believe it does threaten human health. This is because bacteria have a penchant for sharing genes with one another, even across different bacteria species. Most of the bacteria that develop antiobiotic resistance do not infect humans, but they can easily pass along this antibiotic resistance to genes that do. How likely is this? It is difficult to say, so why would we risk the emergence of incurable bacterial infections just so livestock can grow a little faster?, some contend.

Other growth promotents

Growth hormones are not used in pork, chicken meat, or chicken egg production. This is partially due to their ineffectiveness and partially due to the fact these animals are slaughtered at an earlier age.

A variety of non-hormone growth promotents are sometimes used though. Consider beta-agonists, which are compounds that bind on fat receptors of cattle, causing the animal to reduce its production of fat and redirect these nutrients to the production of muscle. One beta-agonomist sold as Zilmax in the beef industry worked great and was quite popular. However, it was eventually understood that it also caused lameness in cattle. Recognizing this the company selling Zilmax removed it from the market. So while growth promotents may be perfectly safe for humans we need to pay heed to their impact on animals as well.

A similar beta-agonist used in pork production is named ractopamine. As with beta-agononists in the beef industry, their use is regulated such that any amounts of the compound in meat consumed by humans will be very low and not threatening to health, but still their use is hotly debated. While it helps pigs grow muscle it creates stress for the pigs, and a number of countries that import our pork have banned its use. Currently, 160 countries have banned its use while 27 (including the US) have deemed it safe.

Some producers will add probiotics to animal feed. These are live bacteria that promote growth, and adding it to animal feed differs little from the human consumption of unpasteurized yogurt. There are also prebiotic additives, which encourage the growth of beneficial bacteria in the animals' gut. Adding acids like citric acid can alter the pH of the stomach, which also benefits helpful bacteria and stymies the growth of bad bacteria like E. coli and salmonella.

Figure 5—Feed additives other than antibiotics and hormones in swine production

A variety of other additives can be useful, like sweeteners that encourage animals to eat more, antioxidants, and natural oils.

Knowns and unknowns

Based on the science that we know, the hormones and non-antibiotic growth promotents are almost certainly safe—so long as they are applied according to regulations (a qualification that must always be added). The dangers posed by antibiotics are less clear.

Why, then is the use of hormones so controversial? At higher-end grocery stores you often see meat labeled as 'no hormones added', a label that usually allows the store to charge high premiums. Moreover, the European Union has banned the use of such hormones, and have long erected import restrictions on US beef because the US beef industry does used them. If the science is so clear on hormones, why all the disagreement and fear?

I don't have all the answers, but I will point you to one thing. This article has told you that 'the science' is perfectly clear that hormone use in the beef industry is safe. Well, we used to feed rendered sheep carcasses to cattle as well, and in the early 1980s I would have said 'the science' says this is perfectly safe as well, because at the time that seemed to be the case—but the science was wrong. What we didn't know was that this can cause Bovine spongiform encephalopathy (BSE) in both cattle and in humans who eat beef from teh cattle. This disease can incubate for 2-8 years, and when symptoms show there is nothing that can be done. The nervous system of person or animal affected deteriotes, and the brain deteriotates, looking like a sponge.

BSE, also called Mad Cow disease for how the infected animal behaves, is thought to be caused when protein from sheep infected with a scrapie disease is are fed to animals. This disease was first detected in 1986 in Great Britain and has since infected over 190,000 people. Once detected it was quickly brought under control by the mass slaughter of over 4 million possibly infected cattle, and strict regulations on how rendered animal carcasses can be used in animal feed. This is probably why some meat companies boast on their package labels that the animals were only fed a vegetarian diet.

Figure 6—When 'irrational' fears are wise

It is thus not unreasonable for someone to look at the failure of science to predict Mad Cow disease and question if we truly know enough to properly regulate hormone use, antibiotic use, and the use of other feed additives in livestock production. Given that Mad Cow disease had much larger impact in Europe than the US, it is also understandable why Europeans are more wary of hormones, antibiotics, and feed additives than Americans.

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