Many pets suffer recurrent skin problems relating to allergies. Allergic reactions are caused by overzealous response of the body’s immune system to a foreign substance (antigen). Frequently, the instigating factor(s) in allergic reactions can come from the food we are feeding our pets. When the immune system is exposed to certain foods, it may produce antibodies directed against that substance. On repeated exposure, these antibodies cause the release of chemicals that cause the allergic symptoms. In most cases, the offending antigen is related to the protein component of the food. Certain ingredients in pet food are more digestible than others. Feeds that have lower digestibility leave more residues in the intestine that may promote allergic reactions. For the most part, no one food is known to be more “allergenic” than another. However, since many pet foods contain similar ingredients (corn, soy, wheat, beef, chicken) if may appear as if these items are more frequently related to allergies.
The symptoms of food allergies mimic those of inhalant allergies. In fact, many pets that have food allergies will also have inhalant allergies and vice versa. The following is a list of the common symptoms seen with food allergy dermatitis.
- Chronic ear infections
- Chronic itchiness (esp. around head and neck)
- Licking the feet
- Skin pigmentation (blackening)
- Greasiness of the coat
- Flakiness of the skin
- Bad skin odor
- Sores on the skin
Most often, there is no real seasonal change in the symptoms of food allergy (unless the pet also has inhalant allergies).
How does our veterinary team diagnose food allergies?
Diagnosis of food allergy is not a simple matter. While there is a blood test that purports to test for this problem, it has not been shown to be reliable and is therefore not used frequently. The only way our veterinarians can truly tell if a pet is food allergic, is to use an elimination diet. This means that we must eliminate all the foods that the pet has been accustomed to eating and replace them with a new diet that is less likely to be allergenic. An ideal “non-allergenic” diet would consist of highly digestible feeds to which the pet has never or rarely been exposed.
The body’s immune system is very effective at recognizing foreign proteins. However, it has been shown that if the protein molecules are small enough (less than a molecular weight of around 8,000 Daltons), the immune system will ignore the protein and not make a response to it. Based on this information, Hill’s Pet Nutrition has developed two diets that we employ to both test and treat suspect food allergic pets. These diets are called Z/D (for zero antigens) and Z/D ultra. In both of these diets, Hill’s has taken the protein components and broken them down (by a process called hydrolysis) into fragments that are smaller than the 8,000 Dalton threshold needed to produce an allergic reaction.
In the Z/D product, potatoes are used as the carbohydrate source since most pet foods do not contain potatoes. In the Z/D ultra, even the carbohydrate source has been broken down so that there are no protein fragments larger than 6,000 Daltons.
When our veterinarians are attempting to make the diagnosis of food allergy, we feed only the Z/D or Z/D ultra diet. No treats, table food, snacks etc will be given during the first 2 months of the diet challenge. If the symptoms improve or disappear during this elimination trial, we have good evidence that the problem is food related. If we want to be certain, we can re-introduce the original food to the pet and observe for recurrence of symptoms. The itchiness will usually recur within a week or two.
How do our veterinarians treat suspect food allergies?
Once the diagnosis of food allergy has been made, our veterinary team generally continue feeding the Z/D diet to avoid further allergic symptoms. Sometimes we can try alternative feeds that do not have any of the ingredients found in the original offending diet. Unfortunately, pets that have a tendency to food allergy may become allergic to any of the new diets unless they have the unique protein components found in the Z/D diets shipped to us. Because there are no preservatives in the serum, it must be refrigerated and there is a very small chance of infection associated with the injections. You will be taught proper technique in handling the serum, which should minimize this risk.
What does our veterinary clinic take care of my pet’s skin problem while the food trial is proceeding?
During the original elimination diet trial, we will use various drugs and products to help relieve your pet’s suffering and clear up pre-existing lesions. These drugs typically may include Prednisone (a form of cortisone), Cyclosporin or Atopica antihistamines, medicated shampoos and conditioners, and essential fatty acid supplementation.