Soy Allergies in Dogs

The canine immune system is an integral part of a dog’s defense system against diseases and illness. However, in some cases, these protective mechanisms can instead work at the animal’s detriment. 

Soy allergies are an example of this – where the body treats the soy protein as an allergen causing hypersensitive reactions resulting in itching, pruritus, and distress for your pet. Although this can not be cured, it can be managed well through diet to minimize exposure and symptoms.

Hypersensitivity to certain foods is commonly seen by veterinarians, with soy protein as a recognized allergen for dogs. Allergies can lead to discomfort and stress for your pet. If you suspect your dog may be having a reaction to soy based food, take him to the veterinarian for an allergy evaluation.

The most common presenting symptom of food allergies is itchy skin. The resulting scratching and self-trauma often lead to recurrent secondary infections. Symptoms include: 

• Generalized, non-seasonal pruritus that is often corticoid-resistant 
• Ear canal infections (characterized by head shaking and scratching at ears)
• Obsessive licking leading to hair loss 
• Secondary ear infections with bacteria or yeast
• Self-trauma 
• Excessive discharge of sebum (known as seborrhea)
• Recurrent pyoderma, often needing antibiotic treatment
• Blepharitis, the inflammation of the eyelids 
• Vomiting and diarrhea 

Types

Food allergies are most commonly caused by protein sources.  Although some dogs are diagnosed under one year of age, many patients are fed the protein for at least two years before developing a sensitivity. Proteins found to often cause food allergy in dogs are:

• Soy bean
• Beef
• Pork
• Wheat
• Chicken
• Milk
• Egg
• Fish
• Lamb

Soy proteins are commonly found in commercial dog food in the following forms:

• Soybean meal & germ meal
• Soy flour
• Soy grits
• Soy protein concentrate 
• Soy isoflavones

Ten percent of allergies in dogs are caused by diet. Although it appears more common in some breeds, there is no strong research that shows breed, sex or age bias. However, there have been reports that state the Labrador Retriever, Cocker Spaniel, Soft Coated Wheaten Terriers and West Highland White Terriers may have a predisposition to food allergies. A known risk factor is existing impairment to mucosal barriers caused by illness such as parvovirus. In addition, pets who have other allergies, such as flea allergic dermatitis (which occurs for 20-30% of soy allergy patients), are at risk for allergies of varying types.  

The canine immune system is an integral part of a dog’s defense system. It is estimated that over half of the body’s white blood cells, which protect your dog against disease and illness are in the digestive system. It is here that protein is broken down by the process of digestion into amino acids which are then absorbed by white blood cells. When not broken down effectively they are seen as antigens, triggering an immune response. This immune-mediated attack intensifies over time, increasing the symptoms for your pet.

When you bring your dog to the clinic, the veterinarian will begin with a physical examination, carefully looking over your pet’s skin. As the disease can often mimic or coincide with atopic dermatitis and flea allergy dermatitis, your veterinarian will need to differentiate from these illnesses. In addition, your veterinarian may want to do blood tests, urinalysis, and analysis of a fecal sample in order to rule out underlying illnesses that may be present concurrent with the allergy.

The distribution pattern of pruritus (severe itching of the skin) is often what suggests food allergy dermatitis in canines, as well as the non-seasonal presentation of the skin irritation. In some cases, dogs will present with chronic ear infections as the only symptom.

As serologic and intradermal testing has been shown to be unreliable in some cases, the preferred method of diagnosis is through an elimination diet. An elimination diet needs to be nutritionally complete and balanced and should only contain novel ingredients that have not previously been fed to your dog. Home made diets are considered the gold standard for treatment, however, these can be time consuming and difficult to prepare. There is a range of commercially available diets your veterinarian will be able to recommend. It is vital during this time that all other food sources are excluded from your dog’s diet, including treats. Make sure that all family members adhere to the elimination diet, and refrain from giving your dog any supplements or medications without veterinary approval.

After two months on the elimination diet, the skin condition of your dog will be reassessed by your veterinarian. If your dog’s symptoms have disappeared, the common allergens (including the suspected soy) will be individually re-introduced into your dog’s diet. If symptoms reoccur after soy protein is re-introduced, the diagnosis of soy allergy can be made.

Diet

Through the elimination diet, clinical symptoms should disappear within 14 days. Following this diagnosis, a diet can be found that contains other sources of protein in order to eliminate soy for long-term management. As with the elimination diet, no other foods or treats should be given. As new food allergies can develop over time, it is vital for you to monitor your pet for reactions to the new diet. If symptoms begin to develop, a rotational diet of different proteins may be considered by your veterinarian. 

Medication

Pruritus caused by food allergy is often corticoid-resistant so this is considered an ineffective treatment. Secondary infections caused by both yeast and bacteria are common and may need antibiotic or antifungal treatment; your veterinarian will prescribe as needed dependent on the condition of your pet’s skin and whether there are secondary infections present.

Additional Care 

Other treatments that may be recommended by your veterinarian are Omega-3 fish oils, which have been shown to be effective as an anti-inflammatory for pruritic skin disease in dogs, and shampoo therapy with oatmeal products, which may give your pet some relief to itching during the reintroduction period.

Unfortunately, there is no cure for soy allergies. However, the condition can be managed by removing it from your pet’s diet. Your veterinarian will recommend a nutritionally complete and balanced, commercially available diet that is free of soy proteins. As with the elimination diet, it is vital that this is the only food given. It is important to be aware that flea hypersensitivity often occurs alongside food allergy making regular flea treatment essential for your dog’s skin health.