Antibiotic Use in Pets

Sharon M. Gwaltney-Brant, DVM, PhD, DABT, DABVT

Date Published: 01/28/2019

Antibiotics are used to treat bacterial infections. They kill invading bacteria without killing the surrounding cells. Antibiotics are made both from living organisms such as fungi, molds, and certain soil bacteria as well as synthesized in a laboratory. Each antibiotic only works on certain types of bacterial infections, so the selection of which one to use and at what dosage depends on the type of infection and how bad it is.

Antibiotics are useless against viruses and will not cure viral infections. Previously, people and pets with viruses were given preventive antibiotics to prevent secondary infections, but this approach is not favored anymore because of the bacteria’s ability to develop antibiotic resistance.

How they Kill Bacteria

Each antibiotic uses a different mechanism with which to kill bacteria. Some work by preventing a bacterium from building a cell wall, some by dissolving bacteria’s membranes, and some affect the way the bacteria build protein or copy DNA. That’s why it’s most effective to culture the infection and know exactly what type of infection is present rather than using a generic broad-spectrum antibiotic; however, sometimes a pet must be started on a broad spectrum antibiotic before the culture results have returned. The earlier any infection is treated, the easier it is for antibiotics to treat it because there are less bacteria needing to be killed.

Antibiotic Overuse

Antibiotic resistance occurs when bacteria develop the ability to survive the drugs designed to kill them, resulting in failure to cure infections. This is an important reason not use antibiotics unless your pet truely needs them.

A major contributor to antibiotic resistance is failure to finish an entire prescription, which allows surviving bacteria to grow in number and in strength. Antibiotics first wipe out bacteria that are easiest to kill, but there will always be some bacteria that are able to survive the initial effects of an antibiotic. If the antibiotic is stopped before these more resistant bacteria have been killed, they will reproduce and create a generation of bacteria that is more resistant than the previous generation. This process is sometimes repeated to the point where we accidentally create bacteria that are so strong that they no longer respond to that antibiotic. To make things even worse, some bacteria can pass their resistance directly to other bacteria.

Let’s say your pet has an infection. You give him an antibiotic that kills 99.999% of the bacteria, which is generally good because killing off that many allows the immune system come in and take care of the rest. But your pet seems fine and you forget and skip the last few pills. Unfortunately, killing 99.999% of bacteria isn’t enough because if the infection has several trillion bacterial organisms, the remaining 0.001% can still number in the millions. In the absence of the antibiotic, those remaining bacteria can flourish, and by the time you notice signs of an infection – which you may think is new, although it isn’t necessarily – it will be harder to get rid of it. Any time you give antibiotics to your pet or a human family member, be absolutely certain to finish all the pills provided in the prescribed timeframe, even when the patient feels better. Drug-resistant infections, such as methicillin-resistant Staphylococcus aureus (MRSA) are more difficult to treat, but they often can still be successfully resolved if treated promptly.

Side Effects

Side effects vary from drug to drug. While people can say, “That pill gave me a stomach ache,” pets obviously cannot, so we really don’t know the full extent of side effects. In general, side effects from antibiotics used in veterinary medicine tend to be uncommon and mild. One of the more common side effects of antibiotics in pets is vomiting in reaction to nausea.

For example, the most common side effect of amoxicillin tends to be nausea, which causes pets to vomit, but giving it with food seems to help prevent the nausea. Dogs being treated for Pseudomonas ear infections require very high doses of enrofloxacin, so nausea may occur, but it’s not likely at the lower doses. Sulfadimethoxine may cause crystals or stones in urine in certain individuals, whereas tylosin may falsely raise the values in liver blood tests. Side effects of metronidazole can be neurologic: staggering, head tilt to one side, dilated pupils, back and forth eye movements called nystagmus, and even seizures (particularly in cats). As with any drug (or food for that matter), individual animals may develop hypersensitivity (allergic) reactions to particular antibiotics. Mild allergic reactions may lead to vomiting, hives, itchiness, and reddening of the skin, while more severe allergic reactions can result in severe skin reactions, low blood pressure, collapse or shock; fortunately, severe allergic reactions to antibiotics are pretty rare.

To see what common side effects are possible with the antibiotic your pet is receiving, ask your veterinarian or look them up at the manufacturer’s website.

Missed Doses

Most antibiotics are administered anywhere from one to four times a day, but what do you do if you’ve missed giving a dose? That really depends on the drug and the infection being treated; in the majority of cases, you can just wait and administer the next dose at the regularly scheduled time. Antibiotics tend to have wide margins of safety, so giving your pet one a few hours after you were supposed to and then giving the next one at the proper time is usually not going to cause a problem. Instructions are printed on pharmacy sheets that usually accompany a drug but if you don’t receive one with the prescription, call whoever dispensed it to ask. Never double a dose to make up for missed doses, as you run the risk of creating side effects.

However, if your pet has a serious infection such as pneumonia and a dose is missed, it might not be wise to allow the blood levels of antibiotic to drop; in that case it’s best to contact your veterinarian for advice.

Friendly Bacteria

Not all bacteria cause infections; many of them are considered “friendly.” Friendly bacteria help keep us healthy in many ways, so when antibiotics kill friendly bacteria, your pet can lose these benefits. For instance, friendly bacteria in the digestive tract aid in digestion and help synthesize essential compounds necessary for health; antibiotic therapy may kill off some of these friendly bacteria, causing diarrhea. Probiotics are mixtures of microbes that are thought to contribute to digestive health and that may be helpful for pets taking antibiotics. Talk to your veterinarian about whether probiotics are useful for your pet’s situation and which ones are best for your pet.

Used correctly, antibiotics are the big gun in medicine’s ability to heal infections. Used incautiously and when not necessary, antibiotics can cause some difficult problems, such as bacterial resistance. Ask questions if you are not sure what to expect for side effects or if you miss a dose. Administer the entire number of pills provided to your pet to avoid creating bacterial resistance, for everyone’s sake.

Adrenal Gland Disease in Ferrets

Karen Rosenthal, DVM, MS

Date Published: 11/04/2019
Adrenal gland disease (AGD) in ferrets is one of the more common conditions that affects ferrets in North America. The signs are due to an abnormal production of sex steroids and androgrens but we do not know why the adrenal glands form tissue that causes this production. These steroids can lead to numerous disease conditions throughout the body. The average age that AGD occurs in ferrets is 3-4 years old. Adrenal gland disease may be more common in ferrets that have been spayed or neutered but since most pet ferrets are desexed, it is difficult to know if this statement is true.

Adrenal Glands

Ferrets, like most mammals, have two adrenal glands. Each gland is situated near the front edge of the corresponding kidney. Adrenal glands are small organs that secrete specific hormones to help the body maintain certain functions.


Signs of AGD in ferrets can include hair loss (referred to as alopecia) that typically starts on the tail and can include the entire rest of the body. About 30% of the ferrets with AGD are itchy. Most females have an enlarged vulva and some male ferrets have difficulty urinating due to an enlarged prostate gland. About 30% of ferrets with AGD will manifest some signs of sexual behavior such as aggressiveness towards other ferrets or animals.
These signs are all due to the increased concentration of sex steroids in the bloodstream.


AGD is characterized by visible enlargement of one or both adrenal glands. The cause of the enlargement can be benign or malignant but even if the cause is malignant, the cancerous adrenal gland cells rarely spread to other areas of the body. The underlying cause for the transformation of a normal adrenal gland into a diseased one is unknown. Theories on why this occurs includes genetics (e.g. inbreeding); spaying or neutering at an early age; or prolonged exposure to daylight (i.e. increased photoperiod). The studies necessary to determine the ultimate cause of AGD have not yet been done.


A physical examination by your veterinarian coupled with typical signs is often enough to diagnose AGD. Hormonal blood testing can be used to confirm it but the disease is usually so obvious that it is typically unnecessary to run these tests for a firm diagnosis. Other lab work, such as a complete blood count (CBC) and plasma biochemistry, will help assess the general health of the ferret. Diagnostic imaging, such as radiographs and/or abdominal ultrasound, can be used to confirm the diagnosis, check for other disease conditions, and determine if one or both adrenal glands are diseased.


It is possible to cure AGD with surgery. Adrenalectomy is a procedure that removes the diseased adrenal gland or or glands. In some cases, only part of a diseased adrenal gland is removed, such as when surgery is too difficult or risky for full removal. If signs continue after this type of surgery, medical therapy may also be needed. Most ferrets do well with surgery but the risks increase if the ferret has other diseases.

Medical therapy is another option but does not cure AGD. In the best possible case, medical therapy can limit or reverse the changes due to AGD. Medical therapy does not prevent the diseased glands from growing, and so over time it is likely that signs will recur. Medications that can be effective in ferrets includes those that have an effect on sex steroid release such as gonadotropin-releasing hormone (i.e. GnRH) agonists (e.g. leuprolide acetate or Lupron® and deslorelin acetate implants or Superlorin®); androgen receptor blockers (e.g. flutamide or Eulexin® and bicalutamide or Casodex®); and anti-androgen drugs (e.g. finasteride or anastrozole or Arimidex®). Some veterinarians are of the opinion that early treatment with GnRH agonists could prevent adrenal gland disease from developing, but evidence in the North American population of pet ferrets is lacking and the long-term effects are unknown at this time. Melatonin implants, which have an effect on photoperiod, may occasionally be helpful.

Some owners opt for no treatment. In some cases, the ferret may have an acceptable quality of life with AGD if the only sign might be hair loss. Once the ferret exhibits signs from AGD that negatively affect the quality of life, then most people agree that some action must be taken. Euthanasia should be considered when a good quality of life is no longer possible. This can occur when medication is no longer effective, when surgery is not an option, and if an owner feels the quality of life has suffered too much.


Some researchers recommend not spaying or neutering ferrets but there is not enough evidence to prove this decreases the risk of a ferret developing AGD. Many owners object to the strong musky odor of intact male and female ferrets. Plus, intact female ferrets must be bred or medically taken out of heat or they will develop a fatal anemia associated with prolonged heat.

Adrenal Gland Disease in Other Animals

Adrenal gland disease that results in overproduction of hormones in other animals is often called hyperadrenocorticism or Cushing’s disease. While the disease seems similar to AGD in ferrets, the signs, cause, and treatments are significantly different.

AAFCO Pet Food Labeling

Mark Rishniw, BVSc, PhD, DACVIM (SA-IM), DACVIM (CA)

Date Published: 11/21/2018
Pet food marketing can get confusing. The labeling does not provide detailed nutritional information and it’s easily misunderstood by consumers. Try as you might, sometimes reading the label doesn’t give you enough answers. However, the more you know about what pet food labels indicate – and don’t – the better off your pet will be.

What is AAFCO?

AAFCO is the go-to organization for understanding animal feed, including food for pets. It does not regulate or inspect anything, nor is it a government agency. It is a group whose members are government agencies representing the 50 states, Canada, and the federal government. It is not a regulatory body, and has no ability to monitor or enforce specific food manufacturing procedures. Animal feed specialists indicate to them what is appropriate for a specific species, and AAFCO provides model feed laws.

State feed control officials can choose to adopt these model feed laws and individual states can enforce them. There is no law that says manufacturers must follow their guidance. AAFCO does not approve or certify any pet food, treat, or supplement products. The FDA, not AAFCO, regulates pet food, and FDA is a member of AAFCO.

If the manufacturer has followed AAFCO recommendations, they can say so on their product packaging. That is one way consumers can tell which manufacturers follow the best guidance in the industry.

AAFCO does not necessarily ensure food adequacy and safety, but relies on current scientific knowledge to provide guidelines for pet food composition which, if followed, minimize the risk of malnutrition. On the other hand, the FDA enforces food safety through the Federal Food Drug and Cosmetic Act, which demands that pet foods, like human foods, be “pure and wholesome, safe to eat, produced under sanitary conditions, contain no harmful substances, and be truthfully labeled.” Therefore, pet food manufacturers are legally responsible for providing nutritionally adequate, safe and wholesome products that conform to local, state, and federal law.

AAFCO requires nine components to be printed on a pet food label:

  1. Brand and product name
  2. Net quantity statement
  3. Manufacturer or distributor information
  4. Calorie content statement
    1. Energy content on a kcal/kg and kcal/common unit as fed basis as well as how this was determined (measured or calculated).
  5. Nutritional adequacy statement
    1. Specifies whether the product carries a complete and balanced claim, and if so, how the claim was substantiated as well as the species and life stage for which the product is intended.
  6. Guaranteed analysis
    1. Minimum crude protein and crude fat and maximum moisture and crude fiber (as fed basis) are required; other nutrients are optional.
  7. Ingredient list
    1. Must be listed in descending order of weight; ingredients must be as defined in AAFCO book; not possible to tell relative contributions of ingredients to any particular nutrients (the ingredient list is not a recipe). Note that ingredients as defined in AAFCO are not often similar to those typically used/defined for human foods; for example, “chicken” must include both flesh and skin and can include bone.
  8. Species designation
  9. Feeding directions
    1. Must be given for each life stage if diet is formulated for more than one.
    2. Not detailed, target animal weights can be given as wide ranges, and no requirement for specific equation to use to determine energy needs of target animals.

What are the different AAFCO nutritional adequacy designations for pet foods?

There are four possible AAFCO nutritional adequacy statements that can appear on pet food labels. These must be printed verbatim as one of the following:

  1. [Diet X] is formulated to meet the nutritional levels established by the AAFCO [Dog /Cat] Food Nutrient Profiles for [gestation/lactation / growth / maintenance / All Life Stages]
    1. if the life stage is growth or all life stages, the claim must also include one of the following depending on calcium content of the product (maximums vary):
  2. “including growth of large size dogs (70 lb or more as an adult)”
    1. “except for growth of large size dogs (70 lb or more as an adult)”
      Animal feeding tests using AAFCO procedures substantiate that [Diet X] provides complete and balanced nutrition for [gestation/lactation / growth / maintenance / All Life Stages]
  3. [Diet X] provides complete and balanced nutrition for [gestation/lactation / growth / maintenance / All Life Stages ] and is comparable in nutritional adequacy to a product which has been substantiated using AAFCO feeding tests.
  4. This product is intended for intermittent or supplemental feeding only.

How are AAFCO feeding trials conducted?

The guidelines for an AAFCO feeding trial vary depending on the diet type being evaluated. There are four protocols: maintenance, growth, gestation/lactation, and all life stages. Although the minimum standards for each type of trial must be met, companies may add on other components to a feeding trial, such as plasma amino acid measurement, digestibility studies, full blood chemistry panels, and complete blood counts to gain additional information about the suitability of their diets for the life stage being tested.

Foods can be put through AAFCO feeding trials even if they do not qualify for a “formulated to meet AAFCO” feeding statement due to deficient or excessive levels of nutrients. One example is veterinary therapeutic diets formulated for chronic kidney disease, which are intentionally formulated to contain phosphorus (+/- protein) at concentrations below the AAFCO Food Nutrient Profiles for adult maintenance; many of these have passed maintenance feeding trials and thus have a “feeding trial” nutritional adequacy statement on the bag. If they have not undergone feeding trials, they must carry the statement: “This product is intended for intermittent or supplemental feeding only.” Such diets are not allowed to reference the AAFCO Food Nutrient Profiles on the label. Theoretically, the flip side is that diets that fail feeding trials but contain nutrient levels within the specified minimum and maximum concentrations per AAFCO Food Nutrient Profiles can be marketed with a “formulated to meet” adequacy statement. Ideally, diets are formulated to comply with the concentrations specified by the AAFCO Food Nutrient Profiles and then pass appropriate feeding trials.

For adult maintenance canine and feline diets, the feeding trial guidelines are:

  • 8 animals older than 1 yr. must start the test.
  • At the start all animals must be a normal weight and health, and weight is monitored weekly. Complete veterinary examinations are mandated at initiation and completion of the test.
  • A blood test is to be taken from each animal at the start and finish of the test for four parameters: (hemoglobin, packed cell volume, alkaline phosphatase, albumin).
  • For 6 months, the animal must only eat the food being tested.
  • The animals finishing the test must not lose more than 15 percent of their body weight.
  • During the test, none of the animals used are to die or be removed because of nutritional causes.
  • 6 of the 8 animals starting must finish the test.
  • Data are compared to a concurrent control group or to historical colony averages.

For growth canine and feline diets, the feeding trial guidelines are:

  • 8 animals NO older than 8 weeks must start the test. Juvenile animals should be obtained from at least 3 dams.
  • At start all animals must be normal weight & health, and weight is monitored weekly. Complete veterinary examinations are mandated at initiation and completion of the test.
  • A blood test is to be taken from each animal at the start and finish of the test (hemoglobin, packed cell volume, alkaline phosphatase, albumin).
  • For 10 weeks, the animal used must only eat the food being tested.
  • During the test, none of the animals used are to die or be removed because of nutritional causes.
  • 6 of the 8 animals starting must finish the test.
  • Data are compared to a concurrent control group or to historical colony averages

For reproduction canine and feline diets, the feeding trial guidelines are:

  • 8 animals older than 1 year and on at least their 2nd heat must start the test
  • At start all animals must be normal weight & health, and weight is monitored weekly. Complete veterinary examinations are mandated at initiation and completion of the test. Offspring are examined within 72 hours of birth and at the end of the test.
  • A blood test is to be taken from each animal at the start and finish of the test (hemoglobin, packed cell volume, alkaline phosphatase, albumin).
  • Litter size is recorded.
  • From onset of estrus to 4 weeks after parturition, the animal (and offspring) used must only eat the food being tested.
  • During the test, none of the animals used are to die or be removed because of nutritional causes.
  • 6 of the 8 animals starting must finish the test.
  • Data are compared to a concurrent control group or to historical colony averages.

Do AAFCO feeding trials accomplish what they claim to accomplish?

Many pet owners and clinicians have raised the concern that AAFCO feeding trials do not represent what really happens in a pet’s life, i.e., that feeding a diet for six months is not the same as feeding a diet for 10 years. That is true. However, although AAFCO trials are imperfect, they do identify most serious acute and semi-acute nutritional deficiencies or excesses, and some minor ones. Furthermore, manufacturers are free to supplement the minimum protocol requirements with additional measures of nutritional adequacy. Also, consider that diets for growth, gestation/lactation, or all life stages get tested more rigorously compared to maintenance since the nutritional demands of those animals are greater.

Evaluation of diets under AAFCO guidelines also includes examination of the nutrient content of the diet being tested. The nutrient content can be determined either from testing a sample of the finished diet or by using the nutrient content of the individual ingredients in the food to calculate the diet composition. The latter is less desirable, since ingredients are inherently variable in nutrient content and because processing and nutrient interactions could alter bioavailability in the final diet. There is no requirement for either in vivo or laboratory testing of pet food products if the formulation method of substantiating nutritional adequacy is used.

Some companies have performed lifelong feeding trials to demonstrate that their diets provide complete and balanced nutrition for the expected feeding duration (i.e., “for life”).

How can you identify the pet foods that have undergone “more rigorous” testing of their pet food, rather than just the AAFCO statement on the bag?

Unfortunately, you can’t. Even veterinarians can’t. The pet food label is really a legal document, and is not designed to convey significant nutritional information. As much as some sources (such as internet ranking lists) would like it to be possible, you cannot evaluate ‘quality’ from the label, especially from ingredient lists. You need to consider the manufacturer (reputation, experience, investment in AAFCO trials and research, etc.), cost, availability, and your subjective clinical impressions of how your pets are doing on various diets.

Board-certified veterinary nutritionists in clinical practice are alerted to dietary issues with specific diets because of extensive interaction with clients, practitioners, and each other. Therefore, these specialists are often a reliable resource for determining which diets are causing disease problems.

In addition, the World Small Animal Veterinary Association Nutrition Toolkit developed by the WSAVA Global Nutrition Committee provides many useful nutrition resources including Recommendations on Selecting Pet Foods. This document lists eight questions you can ask pet food manufacturers to help evaluate their suitability:

  1. Employment of a full-time qualified nutritionist (PhD in animal nutrition or board-certified by the American or European specialty veterinary colleges).
  2. Who formulates the diets and what are the credentials of this individual
  3. Location of food production and manufacturing
  4. Method of substantiating complete and balanced claims. If formulation method is used, are the foods analyzed to determine nutrient profile?
  5. Details of quality control measures
  6. Availability of complete nutrient profile (“typical analysis”) for products
  7. Calorie content
  8. Availability of any product research (published in peer reviewed journals or elsewhere).

Dr. Rebecca Remillard (a board-certified nutritionist and consultant for the Veterinary Information Network, the parent of Veterinary Partner) has suggested that companies manufacturing veterinary therapeutic diets generally use the same standards of quality in their over-the-counter diets. It is ideal for a manufacturer to have a qualified nutritionist as a full-time employee rather than just as a consultant. Dr. Cailin Heinze, also a board-certified nutritionist, additionally prefers companies that perform testing above and beyond AAFCO trials, especially with veterinary therapeutic diets. Furthermore, Dr. Heinze looks for company longevity as a sign of a successful track record, and is critical of “guerrilla marketing” in pet supply stores (aggressive, emotion-based strategies directly to consumers). Finally, she looks for companies willing to share full nutritional profiles (e.g. full or typical analysis) of their diets rather than just a guaranteed analysis, and provide updated information with regular batch testing.

Understanding what’s best for your pet isn’t always easy. Oftentimes the only way to get a clear answer to your question is to telephone (not email) the manufacturer. However, the best chance for your pet’s good health is to begin with a food bearing an AAFCO nutritional adequacy statement on its label.