We read and hear terms like “raised without antibiotics,” “antibiotic free,” in the news, on the television and on social media. The fact is reducing antibiotic use can have severe ramifications from an animal welfare perspective. If used properly, antibiotics are effective and safe.
The livestock industry has established withdrawal periods, by law, so there are no antibiotic or other drug residues from products such as Nonsteroidal anti-inflammatory drugs (NSAIDs) or vaccines in our meat or milk. The established withdrawal times are set for each product use for livestock.
Antibiotics are used in animal agriculture in four major ways: disease treatment, disease control, disease prevention, and growth promotion.
Briefly, disease treatment refers to the use of the antibiotic in an ill animal. Disease control refers to the use of the antibiotic in a population of animals during a time of illness. Not all of the animals receiving the antibiotic are necessarily ill at the time of antibiotic administration; this antibiotic use stops the disease from spreading. Disease prevention refers to the use of the antibiotic in an animal or in a population of animals at a time when it is known that the animals are susceptible to disease.
Finally, growth promotion refers to the use of the antibiotic in a low-dose fashion to improve the weight gain and feed efficiency of the animal. All four of these uses result in an improved health of the animal receiving the antibiotic, and all of these uses can be administered via the feed or the water because the only realistic way to give antibiotic to populations of animals, such as a flock of chickens, is through the feed or the water.
Even though all four of these uses can improve the health of the animal, there has still been confusion about them. One area of confusion is related to the amount of antibiotic that is administered.
Because disease control, disease prevention and growth promotion can use smaller amounts of the antibiotic than is given to the sick animal during disease treatment, these uses have sometimes been labeled as “subtherapeutic” or “nontherapeutic”.
These terms imply that the low-dose uses do not have an effect on the health of the animal. As was seen in Denmark and other countries that have limited these low-dose uses, animals receiving an antibiotic at low doses are often healthier than if they had not received the antibiotic, and thus these terms are misnomers.
When an antibiotic is fed to animals for growth promotion or disease prevention, each individual animal is fed relatively small amounts of the antibiotic. Reports that attempt to quantify the total amount of antibiotic fed to animals are often misleading, because it is the concentration of antibiotic to which an individual animal is exposed that affects the development of resistance and not the total amount of antibiotic used in a country during a year.
In Denmark, the total amount of antibiotic administered to animals appeared to decrease following the ban of growth promotion antibiotics. However, when measured as the number of doses administered to animals, there was an increase in antibiotic consumption following the ban.
This is because the treatment of sick animals necessitates a much higher dose per animal than the low amounts given to animals on a per capita basis for growth promotion and disease prevention purposes. The question then becomes which of these uses (low-dose for growth promotion / disease prevention versus high-dose for disease treatment) presents less risk for bacteria becoming antibiotic resistant.
To address this question we must first ask, “What exactly is antibiotic resistance?” A simple explanation is; when antibiotics are used, bacteria that are responsive to the drug are killed, and bacteria that are not responsive (are resistant) survive and reproduce.
Many studies have shown that high doses of antibiotics used for the treatment of disease result in the potential for the development and spread of antibiotic resistance.
Results like these are not easily found for low-dose applications of antibiotics in animal feed. Furthermore, the antibiotics that are used in high doses for disease treatment are often in the same class as those used in human hospitals. Antibiotics used in small doses for growth promotion and disease prevention are often older antibiotics with much less importance to human health. Consequently, does the feeding of antibiotics to animals at low doses increase levels of resistant bacteria that can be transferred to humans via food?
One way to approach this question is through a scientifically rigorous process known as risk assessment. An analysis was conducted to assess the risk that the agricultural use of a family of antibiotics known as macrolide antibiotics poses to human health.
The concern is that agricultural use of macrolide antibiotics, which are also used in human medicine, could compromise the efficacy of these antibiotics in human medicine and potentially increase the number of macrolide-resistant bacterial infections in people.
In this model, all macrolide antibiotic uses in animal agriculture in the U.S. posed a very low risk to human health. Findings such as these have been corroborated by other risk assessments.
How difficult is it to get a resistant infection? For a person to get an antibiotic resistant infection from eating meat, a number of unlikely things must happen: first, the animal must become sick and be treated with an antibiotic.
Then antibiotic resistant bacteria must develop in the animal. Then the bacteria must survive multiple food safety controls during processing.
Also, the bacteria need to survive proper cooking temperatures. Next, the bacteria need to cause an illness in person that is severe enough to warrant medical attention, and finally, the doctor prescribes an antibiotic and the illness fails to respond to treatment because bacteria is resistant to prescribed antibiotic.
So, how difficult is it to get a resistant infection? If meat is cooked properly, the antibiotic resistant bacteria die – breaking the chain of unlikely events. The probability of human illness in the U.S. due to drug resistant food poisoning (campylobacteriosis) is about one in 236 million. Being killed by an asteroid is 1000 times more likely.
Remember, responsible antibiotic usage is about using the right drug for the right bug and for the right length of time. Many times, painkillers, supplements, vitamins or minerals rather than antimicrobials may be the therapy of choice.
Prevention of the disease through vaccination, low-stress weaning and reduced commingling of livestock can also greatly reduce the usage of antimicrobials.
In specific instances, we may be able to actually lower drug costs and have better outcomes while at the same time not contributing to any resistance.
