by: Stephen B. Blezinger

Part 2

In Part 1 of this series we began a discussion on the use of antibiotics in livestock and the debate this practice has incited for years. In particular the use of antibiotics that are fed to livestock and poultry are of particular concern because many individuals feel that it leads to an increased resistance to therapeutic antibiotics by bacteria that affect humans. Most recently the FDA, by judicial order, has reopened the examination of this issue and is moving forward in making significant changes to its rules and guidelines. Subsequently, drug manufacturers, livestock industry members and producers in particular will encounter regulatory changes that will affect the use of these well established management tools.

In Part 2 of this series we will review the use of antibiotics in cattle, both therapeutic (injected and fed) and non-therapeutic (fed used to address sickness or to improve animal performance), applications. The following section, in a question and answer format, was adapted from a particularly useful website,, from South Dakota State University, Department of Veterinary and Biomedical Sciences.

The Basics of

Antibiotic Use in Cattle

What are antibiotics?

Antibiotics are medicines that are given to people and animals to treat or prevent certain illnesses caused by bacteria. Antibiotics either kill or deter the growth of harmful bacteria in animals and people.

Why are antibiotics given to cattle?

Antibiotics are given to animals that are sick, in order to help relieve the pain and distress due to the illness, help the animal feel better, and recover. For the exact same reasons they are given to people. Antibiotics may also be given to animals that are in danger of becoming sick in order to prevent the illness or infection from happening in the first place. As with humans, however, antibiotics do not have any effect on diseases of animals that are caused by viruses or parasites, or other germs besides bacteria. Some antibiotics, for reasons that aren't totally understood, help cattle grow faster and get more out of the feed they eat. These medicines are used at lower concentrations than when they are used to treat illness, and typically are included in the feed that cattle eat. The decision whether to use such products for this, or any other application rests with the individual cattle raiser. Not all producers use antibiotics in this manner. In turn, not all cattle are fed antibiotics.

How are antibiotics given to cattle?

Antibiotics can be given to animals with injections under their skin or in a muscle, orally with boluses (large pills), by mixing in drinking water, or by mixing in feed. Injectable antibiotics are normally used in cattle only when they are sick, or are at high risk for getting sick. Using injectable antibiotics means that the animal has to be held or restrained still enough that the injection can be given in a manner that is safe for the animal and the person giving the injection. This can be an additional stress on an animal, and more work for the producer, so its use is reserved for those animals that really need it. Many products require a prescription from a veterinarian who is familiar with the animals. People who raise cattle develop relationships with veterinarians and consult with them to determine the best options for disease prevention and treatment. Based on these guidelines, cattle raisers can give the antibiotics to cattle themselves at the farm or ranch. The approval of and directions for the use of these products are dictated by the Food and Drug Administration to guarantee the proper use of these products for animal health and to maintain a safe supply of beef. This includes minimum withdrawal periods that ensure no antibiotic residue remains in the beef we eat.

What are some specific examples of the use of injectable antibiotics in cattle?

Injecting antibiotics, compared with offering them in animals' feed, results in a higher concentration in the body for a relatively short period of time. Young calves may need to be treated with antibiotics if they get a case of pneumonia or bacterial diarrhea. Calves that have been recently weaned may need to be treated with antibiotics if they get sick with pneumonia. At any stage of life, calves, cows, and bulls can encounter bacterial infections such as pinkeye, foot rot or infected wounds that require treatment with antibiotics. Examples of commonly used antibiotics for these conditions include penicillin, tetracycline, ceftiofur, florfenicol, tilmicosin, enrofloxacin, and tulathromycin. These treatments are necessary in some cases for the survival of the animal, but also to reduce pain and suffering that these illnesses bring with them.

What are some specific examples of the use of antibiotics in cattle feed?

Not all cattle being raised for beef receive antibiotics in their feed. Cattle feeders may choose to mix these medicines in their animals' feed for several reasons. The period around weaning, or when calves are separated from their mothers, is a time in which antibiotics are used more commonly than other times. The stress of separation, sometimes along with very variable weather conditions (cold, heat, rain, snow) can make calves more vulnerable to pneumonia. For that reason, antibiotics may be included in the feed around that time, in order to prevent pneumonia or help mildly ill cattle recover. Since this illness, if it occurs, occurs in the first two to three weeks after the stress, these uses of antibiotics are short-term, focused around that time period, and fed in higher concentrations. Common antibiotics for this use include tetracycline and some sulfas: related medicines are used in people as well.

Another use of feed antibiotics may occur when calves are growing rapidly and approaching their final weight. Calves can develop abscesses (pockets of infection) in their livers when a high percentage of their diet consists of grain. In some cases these abscesses can cause illness in the calf. They result in the liver not being fit for food. To prevent this condition, antibiotics such as tylosin are fed to cattle late in the feeding period. Tylosin is not used in humans.

As with injected products, the medicines can be used in animal feed is strictly regulated by the Food and Drug Administration.

Is it better for the animal to get antibiotics in the feed, or by another method?

If calves are very sick, they will not eat as much, and would not get enough antibiotic through their feed. In these cases animals need to be treated individually with injections or other methods. Research has long shown that one of the first symptoms shown by a sick animal is reduced feed intake or going off feed altogether. If calves are still eating well, the use of medications in the feed or drinking water is a way a cattle feeder can give medicine to a lot of animals at the same time with no distress to the animal.

Are antibiotics given to cattle the same antibiotics used in people?

Regarding forms of antibiotics available for use in cattle feed, the list of human antibiotics in the table of "Commonly Prescribed Antibiotics" in the Merck Manual for Healthcare Professionals shows that two of the 74, neomycin and tetracycline, are available to be used in cattle feed.

Tetracycline - or rather its relatives, oxytetracycline and chlortetracycline - are used to prevent and treat pneumonia in calves. They are also approved in lower concentrations to help calves grow faster and improve their feed efficiency. Neomycin is a component in a few formulations of cattle antibiotics for growth promotion, but it is rarely used in cattle diets.

Several other common human antibiotics on the list, procaine penicillin, benzathine penicillin, ampicillin, amoxicillin and spectinomycin, are approved for use in cattle are available for use in injectable form. They are not allowed to be mixed in feed. The other antibiotics used for cattle are not on the human list, but some of them are members of drug "families" that include some important human antibiotics. For example, enrofloxacin, an injectable cattle antibiotic, is not used in people, but is closely related to drugs like ciprofloxacin, that is important for people.

Do all cattle need antibiotics in order to stay alive in our current systems of raising cattle?

No. For example, some consumers choose to purchase beef from animals that have never been administered antibiotics in any form, fed or injected. Some ranchers and feedlots raise cattle in a manner that targets this market, which is often referred to as the "natural" beef market.

In most herds, at least a few of the animals have needed an antibiotic treatment at some point in their life, or have needed feed grade antibiotics to prevent a case of illness. Responsible ranchers and feeders, even those producing beef for a "natural" market, give sick animals antibiotics when it's necessary for the animal's well-being (these treated animals are then removed from the group of animals that are marketed as "natural"). Vaccine programs, which prevent diseases and management steps like keeping a closed herd (not buying new animals from outside the herd), are among the many tools used by many cattle raisers to keep animals healthy and avoid the need for antibiotics.

How do antibiotics affect the meat from an animal that is treated with them?

Most antibiotics given to animals end up being absorbed into their bloodstream, but some that are given orally are only active in the gastrointestinal tract and never enter the bloodstream. The antibiotic that is given to an animal is "metabolized," or changed by the chemistry of the body, to forms that may be more effective against the bacteria, more readily distributed through the body, or more easily removed from the body. This metabolism is different for every different antibiotic and for each different route of administration, but its end result is the eventual elimination from the body.

People giving antibiotics to food animals are required to follow a "withdrawal time" after treatment. The withdrawal time is a waiting period after treatment that gives the animal time to reduce the concentration of the drug in its body, and therefore in the meat (or milk or eggs) the animal produces. This withdrawal time is different for each antibiotic, and is set by the Food and Drug Administration after thorough research and review. It reflects the point in time after administration at which the antibiotic is at a low enough level in the animal to not result in safety problems for people eating its products

The US Department of Agriculture's Food Safety Inspection Service (FSIS) tests for the presence of antibiotics in the carcasses of animals used for meat. While not every animal is tested, carcasses are tested at random, along with "targeted" sampling of carcasses from farms that have had problems in the past. Fines and prison time are possible for people selling animals with levels of antibiotics over the limit. The numbers of violations are extremely low, and are published regularly on the FSIS website. The cattle industry and in fact all of the meat industries, as well as the regulatory bodies take this issue very seriously.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at or at (903) 352-3475. For more information please visit us on at www.facebook/reveille livestock concepts.

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