Technological advances in animal agriculture have created a second-to-none food system that is phenomenally safe and produces the cheapest food in the world. From the advent of cross-breeding, artificial insemination (AI), bulk tanks, vaccines, antibiotics and growth promotants, the U.S. is the envy of all in its ability to efficiently produce high-quality food.

Yet, with every advance, there are those who question whether the new technology threatens food safety. This was true when AI became widely used by the dairy industry in the 1940s or beef growth promotants became common in the 1960s. Certainly there have been hiccups along the way when our understanding and or application of science did not get it right. Damage to animals, the environment or human health has occurred. However, I would argue that at least regarding food availability and safety, the good has outweighed the bad. Over the next two columns, I would like to address two oft-misunderstood technologies that have led to some impressive advances in beef production: antibiotics and growth-promoting hormones. This month, the focus is antibiotics.

Photo: CSA-Images/istock


We have not been using antibiotics for very long. In 1928, penicillin was discovered, followed by sulfas in 1935 and streptomycin in 1943. In the early 1940s the military began to ramp up production of antibiotics in preparation for World War II. In 1942 the first civilian was treated for a strep infection. She survived and lived until 1999. The benefit of antibiotics to human health is demonstrated by the fact that the leading causes of death in 1900 were infectious diseases – pneumonia, tuberculosis, diarrhea and enteritis. In 1997 the leading causes of death were noninfectious: heart disease and cancer.

In 1946, one of the first uses of antibiotics in animals was to treat mastitis in a dairy herd owned by the governor of New York, Thomas Dewey.

According to the FDA, antibiotics can be labeled for three uses:

  1. Therapeutic: Treatment of disease
  2. Subtherapeutic: Prevention and control of disease
  3. Production: Improved growth and feed efficiency

Why are antibiotics used in food-producing animals?

The vast majority of animals treated with antibiotics are done so to maintain animal health. Just as humans get sick and at times require antibiotics to fight infection, animals are no different. In fact, a 2007 study conducted by the Animal Health Institute showed that 87 percent of all antibiotics used in animals were used to treat disease. I think most people are OK with treating disease, but what about using antibiotics for production purposes only?

This issue will be resolved as of Jan. 1, 2017. On this date, with the exception of ionophores (trade names Rumensin and Bovatec), any antibiotics currently labeled for the sole purpose of improving growth and or feed efficiency will no longer be legal. Put simply, going forward, antibiotics will only be allowed for the treatment, control or prevention of disease.

Public concerns

Antibiotic residue. The journey from an idea to animal use is a long, arduous one. The steps include animal testing to determine the level of the drug that has no toxic effect on the animal. Next a safety factor is applied. This can be as high as 1,000, which results in a 1,000-fold reduction in the allowable level. Then this level is multiplied by the average weight of a human (132 pounds) to determine average daily intake of the drug with no adverse effect. The final step is a study where animals receive the drug and are then sacrificed at different time points to determine when the residue drops below the tolerance in the target tissue (edible organ that maintains drug residues the longest, usually the kidney or liver). This process reduces the risk that a given level of antibiotic in meat will be deleterious to human health.

Monitoring residues. The Food Safety and Inspection Service (FSIS) is responsible for assuring the safety of the beef supply. The regulations that they have instituted have resulted in extremely low levels of residues that exceed allowable levels. Inspection involves two steps. First, it’s important to know that every animal that is presented for harvest at a USDA facility is inspected antemortem (alive). If the inspector has any reason to suspect it may have a drug residue, it is tested. Post-mortem, carcasses are tested at random. This procedure has resulted in less than 0.5 percent of carcasses containing a violative residue in 2012.

“Eighty percent of antibiotics sold in the U.S. are used in animal agriculture.” This is a sound bite used by activists that, on its surface, is true, but upon closer investigation leads to a completely different conclusion. The table at right was borrowed mostly from Western Kentucky University’s Dr. Nevil Speer and appeared in “Feedstuffs” (April 29, 2013). To date, I’ve been unable to locate more recent data. In 2011, 30.3 million pounds of drugs were sold for animal use and 7.2 million pounds for human use. This is a ratio of 4:1.

A class of drugs needs to be removed as they are not used in human medicine, remain in the digestive system (that is, they do not end up in the animal tissue) and, with extensive use, have not developed resistance. This class of antimicrobials, called ionophores, when removed, result in a ratio of 3:1. Finally, it is important to understand that animals are dosed based on weight – a 1,000-pound steer will receive more antibiotics to treat disease than a 500-pound steer. This is not the case for humans upon reaching a certain weight or age. Considering this and accounting for the fact that there are 135 billion pounds of animals and only 46.5 billion pounds of humans, the final ratio is 1:1. Conclusion: on a per-pound basis, medically important antibiotics are used at the same level in humans as animals.

Antibiotic resistance

Mike Apley, DVM, Epidemiologist from Kansas State University, has said much about his understanding of this antibiotic resistance. One of my favorites is “…If you understand antimicrobial resistance, then it hasn’t been adequately explained to you.” To his point, this is a very complex issue and the science is evolving. As such, the best way for me to cover this topic is to present the following comments from the experts:

What we do know

Findings from Princeton Univeristy’s Ramanan Laxminarayan show that resistant bacteria and resistance genes are transmitted directly from farm animals to people in direct contact with them (farm and slaughterhouse workers). In addition, that bacteria is transferred through the consumption of contaminated animal products and possibly the environment.

Other experts like John Mass, DVM, of Veterinary Medicine Extension, School of Veterinary Medicine, University of California-Davis, warn of the misconception of decreasing the amount of antibiotics used in raising cattle leading to the decrease in antibiotic-resistant bacteria that causes disease in people. “There is no evidence that this cause-and-effect relationship exists,” he stated.

“There are no robust data on the relative effects of different types of antimicrobial exposures in selecting resistant organisms. Short-sighted attempts to merely ‘reduce use’ by the most rapid method may result in significant adverse effects on food animal health with little or no benefit to human health,” Apley stated.

According to a 2011 presentation from the “Antibiotic Use in Food Animals” Symposium, livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is a new and potential health concern for persons in the swine/livestock industries, but current evidence indicates it is not a concern for the broader community as it has not been shown to be a significant cause of the overall MRSA burden in humans. Since LA-MRSA is not a food-borne pathogen, it is not a food safety or public health concern.

What we don’t know

For all the knowns, there are also the unknowns. The relative contribution that dose and duration [of antibiotics] have on resistance selection is ill-defined. For example, the effect of duration of therapy on therapeutic outcome [resistance] is ill-defined in both human and veterinary medicine. This was presented at the “Antibiotic Use in Food Animals” Symposium, Oct. 26-27, 2011, Chicago, Illinois.

Laxminarayan stated that due to constant movement of bacteria between animals and humans, the origins and degree of resistant bacteria from animals to humans is still a mystery.

“Given that transmission through these routes is possible, the use of veterinary antibiotics and the growth of resistance in animals certainly impacts human health, but we are still finding out how much,” she stated.

In Part II: Dr. Baker will examine growth-promoting hormones and summarize in the July issue.


Paul D. Virkler, DVM. 2016. “History and how antibiotics function to improve Animal Health,” New York Beef Producer’s Association Winter Management Meeting, Syracuse, NY.

“Antibiotic Use in Food Animals,” National Institute for Animal Agriculture. Symposium White Paper, October 26-27, 2011, Chicago, IL.

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