Back from The Vet: Antibiotic Use in Goats
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Antibiotics have been, and continue to be, a hot button item. Their use, especially in livestock, is becoming increasingly more controversial. As concern for antibiotic resistance rises, federal and state regulations are further restricting their use. Though many goat owners consider their animals pets rather than livestock, they still fall under the same regulation. Goat and other livestock owners must be proactive to ensure the health of their animals is maintained.
Antibiotic resistance in people has been the greatest concern leading to the increased regulation of antibiotic use in livestock. Bacteria are becoming increasingly resistant to treatment using common antibiotics, making infections more difficult to clear. Antibiotics that are medically important in human medicine are those being most regulated at this time. Though use in livestock is likely a small contributor to bacterial resistance in people, careful use of antibiotics is essential to ensuring that they continue to be effective. This One Health approach is important for the future of both human and animal medicine.
The FDA specifies four different acceptable uses for antibiotics in livestock. These uses are: preventing disease, controlling disease, treating disease, and promoting growth. In 2017, the FDA implemented the Veterinary Feed Directive. Under this regulation, medically important antibiotics administered to livestock in feed or water require veterinary prescription or directive. It also prohibits the use of medically important antibiotics to promote weight gain or efficiency. The specified antibiotics must only be used only as necessary to treat a diagnosed medical condition. This regulation was instituted nationwide in the US. Some states, notably California in 2018, have also removed any over-the-counter antibiotics such as penicillin. They require all antibiotic use in livestock to be with a veterinary prescription. These regulations have all been instituted to ensure that antibiotics are used responsibly in livestock.
In those states that still allow over-the-counter use of common injectable or oral antibiotics, responsible use involves knowledge. Prior to the administration of an antibiotic, a livestock owner needs to know what condition they are treating, what the appropriate antibiotic is to treat that condition, and what the appropriate dosage is for that medication. If you are an inexperienced livestock owner, your veterinarian is the best source to help you build a treatment plan for your animals. Choosing the right antibiotic ensures both the health of your animal and the health of others.
The two most common over-the-counter injectable antibiotics are penicillin G procaine and oxytetracycline. Both of these medications can be used for a variety of conditions at different dosages and routes of administration. These medications also have withdrawal times established, prohibiting the consumption of milk or meat products from animals after the use of antibiotics for that time period.
Penicillin G procaine is perhaps the most common over-the-counter antibiotic. Though this medication is a broad spectrum in its bacterial inhibition, it is in a class of antibiotics that has many bacteria resistant to their mechanism of action. This medication is most commonly used to treat clostridial diseases, such as tetanus and enterotoxemia. It is also used to treat listeriosis. The primary route of administration is intramuscular, with the dosage being 22,000 IU/kg. Penicillin comes in a suspension of 300,000 IU/ml. This dosage is equivalent to roughly 0.33ml/10lbs of body weight. When treating these conditions, penicillin must be given every 12 hours to ensure effective concentration within the body. In cases of enterotoxemia, penicillin may also be given orally. Penicillin may also be used to treat some bacterial types of pneumonia, but due to widespread resistance, it may not be ideal as a first choice. After having given penicillin, milk must be withheld from use for human consumption for 120 hours, and slaughter for meat consumption must not occur for 30 days.
Oxytetracycline is the other common over-the-counter injectable antibiotic. This antibiotic is also broad in spectrum of bacterial activity, including some organisms that penicillin cannot treat, such as mycoplasma. There are many bacterial that are resistant to oxytetracycline as well, making careful selection of appropriate animals important. Oxytetracycline treats bacterial pneumonia, gangrenous mastitis, listeriosis, foot rot, and chlamydiosis abortion. The primary route of administration is intravenous, but it can also be administered subcutaneously. The intravenous dosage varies depending upon disease condition from 5-15mg/kg daily. The subcutaneous dosage, used most commonly for footrot, is 20mg/kg every three days. Oxytetracycline commonly comes in a 200mg/ml concentration, but more concentrated varieties are available as well. The milk withdrawal time for oxytetracycline is 120 hours, and the meat withdrawal is 28 days.
Appropriate estimation of weight is important to ensure the correct dosage of antibiotics. Underdosing can increase the occurrence of bacterial resistance. If weighing by scale is not possible, it is better to daintily overestimate than under. By following the appropriate formula for antibiotic dosing, one can ensure that the correct dose is given to each animal. Below is a representation of how to appropriately calculate the dosage of penicillin in a kid.
|Weight in lbs / 2.2 lbs per kg= weight in kg||Weight in kg x mg/kg = mg of medication||Mg of medication / mg/ml of medication= ml of medication|
|15lb kid 15/2.2 =6.818 kg||6.818 x 22,000IU/kg= 150,000 IU||150,000IU / 300,000 IU/kg= 0.5ml of penicillin|
As antibiotic restriction becomes stricter, forethought on the part of livestock owners is essential to ensure continued availability. Livestock owners should make written protocols with their veterinarian for treatment of commonly occurring ailments within their herd, such as footrot and pneumonia. This will allow for rapid treatment of animals with an appropriate antibiotic at the appropriate dosage. In the case of new disease presentations, livestock owners should seek veterinary care to ensure an appropriate disease diagnosis prior to instituting treatment. Despite penicillin and oxytetracycline being readily available, they are not always the best choice for animal health. Hasty use of the wrong antibiotic is not just a waste of money, but can be contributing to antibiotic resistance. Though many states have yet to place restrictions on over-the-counter antibiotics, planning with your herd veterinarian now will ensure that you are able to obtain necessary antibiotics in the future.
Dr. Katie Estill DVM is a veterinarian consultant for Goat Journal, Countryside & Small Stock Journal, and Countryside online. She works with goats and other large livestock at Desert Trails Veterinary Services in Winnemucca, Nevada.
Originally published in the May/June 2020 issue of Goat Journal and regularly vetted for accuracy.