FOOD ALLERGY AND ELIMINATION DIETS

Itchiness is an extremely frequent problem in dogs and cats and is most commonly caused by insects (fleas, mites, lice etc), infectious agents, such as bacteria and fungi, and allergies.  The normal approach when investigating animals with itchy skin is to firstly rule out insect and infectious causes.  After this had been done, veterinary surgeons often make a tentative diagnosis of allergy.  However, to establish a complete diagnosis that allows successful long term management, it is often necessary to determine whether the animal is suffering from food allergy, atopic dermatitis or a combination of the two.  These conditions are clinically indistinguishable and atopic dermatitis can only be definitively diagnose after food allergy has been ruled out.  It is therefore important that a rigorous and logical diagnostic approach is applied when attempting to diagnose food allergy.  This information sheet discusses the many problems and pitfalls which need to be considered before a successful outcome can be expected.

CLINICAL FEATURES

Food allergies that affect the skin of dogs usually present as non-seasonal itchiness.  This may be generalised or restricted to certain body regions such as the ears, feet or perineum.  Commonly secondary problems associated with food allergies in dogs include Staph or yeast skin infections and seborrhoea. Cats with food allergy may have miliary dermatitis, symmetrical hair loss and itchiness.

DIAGNOSIS OF FOOD ALLERGY

Unlike many diseases, there are no laboratory or clinical tests currently available that can be used to diagnose food allergy in dogs and cats. The diagnosis of food allergies is made by putting an animal on a restricted diet trial (elimination diet) to determine if the skin condition resolves. If it does, the animal is placed back on its original diet and observed for signs of a recurrence.  However for the trial to be diagnostic there are many practical considerations that need to be addressed.

HOME COOKED DIETS   

Veterinarians at Canobolas Family Pet Hospital recommend a home-cooked diet trial rather than a commercial diet to definitively rule out food allergy because, this theorectically allows complete control over the ingredients entering the animal's digestive tract.  Also if there is no response to the diet (as occurs in a majority of cases) there is no residual element of doubt that the animal could be reacting to a commercial preservative or additive.

The usual recommendation for formulating home-cooked diets is to restrict the animal to a single protein source, a single carbohydrate source and water.  The choice of these ingredients is bases on a detailed analysis of the animal's previous dietary history.  Typical protein sources include fish, pork, rabbit, venison, turkey or kangaroo.  Beef, chicken and mutton are generally avoided because they are common ingredients of most pet foods.  Typical carbohydrate sources include potato, rice or pasta.  The ratio of protein to carbohydrate is usually about 1:2.

PREPARATION OF HOME COOKED DIETS

The following guidelines apply:

1.      The basic ingredients comprise a single protein source and a single carbohydrate source.  The choice of ingredients is based on the animals' previous dietary history and your vet will advise you on what is best for your pet. 

2.      Excess fat should be removed from meat sources to reduce the chance of digestive upsets

3.      The meat or fish can be microwaved, baked or boiled

4.      The cooked meat should be broken up into small fragments using a mixer or food processor (this is not necessary if minces are purchased)

5.      The carbohydrate source can be boiled, steamed or microwaved

6.      The meat and carbohydrate in the ratio 1 part meat to 2 parts carbohydrate should be thoroughly mixed together so that they cannot be separated by the animal.  Using a food processor at this stage can lead to a diet that lack texture due to a very small particle size.

7.      The final diet should be weighed into appropriate sized portions for the particular animal.  The bags of food can then be frozen until use.

Owners often inquire as to the amount of home-cooked diet to feed.  Some general guidelines as to the quantities of food that are likely to be required for average pets are shown below.  However, as with any dietary advice, the guidelines should be interpreted in light of the animal's breed, level of activity and the climate.  In general, home-cooked diets are nutritionally incomplete and underfeeding is more of a problem than overfeeding.  As a simplified guide, we normally recommend starting with a quantity about half as much again as the animals' previous commercial diet.  Further increases can be made if the animal appears constantly hungry or begins to lose weight.  It is advisable to weigh animals on a weekly basis throughout the food trial in order to monitor body weight. 

APPROXIMATE GUIDELINES FOR FEEDING HOME-COOKED DIETS

PROBLEMS ASSOCIATED WITH FEEDING HOME-COOKED DIETS

There are a number of potential problems associated with the feeding of home-cooked restricted diets that owners should be warned about in advance.  First, the animal may find the food unpalatable and may eventually refuse to eat it altogether.  This is more of a problem with cats than with dogs, but it can occur in both species, especially with previously fussy eaters.  The only solution to this problem is to try an alternative protein source or to switch to a commercially produced limited ingredient diet. However, in some case, it may be necessary to terminate the trial.

If the animal does eat the diet, it may lead initially to digestive upsets such as vomiting, diarrhoea, colitis or flatulence.  These adverse effects can be reduced by introducing the diet gradually over a few days.  If these effects persist, the fat content of the diet should be reduced by remove more of the fat during preparation.

It should also be noted that home-cooked diets contain a higher water content than many commercially available diets, especially if the animal is used to eating a dry food diet.  Owners will sometimes notice a decrease in voluntary water intake which in some cases, may stop altogether.  This can be quite alarming to owners, but is of no significance as long as the animal is otherwise behaving normally. 

Preventing an animal from acquiring other food sources is another major problem encountered during dietary trials.  For dogs, these may be inadvertent treats, kitchen waste, food intended for other pets, pavement waste (eg pizza, kebabs, chips etc) and other animals' faeces.  Free-range cats may also obtain food from neighbours and rubbish bags, or catch wild birds and rodents.  These problems can be partly overcome by strictly monitoring the dog's activity or confining cats to the house.  If part of the animal's routine is based around provision of treats, it is possible to make home-cooked varieties from the single protein source that makes up the diet.  For example, strips of meat or homologous liver can be hard-baked in the oven so that they go dry and crispy.  These can then be offered to dogs instead of chews or biscuits.  However, realistically, it is extremely difficult for an owner to guarantee that nothing else will enter an animal's mouth apart form the diet and water.  Therefore we request that you note down any unauthorised snacks in a diary so that their significance can be discussed when the animal is re-evaluated. 

Home-cooked diets are neither nutritionally balanced nor complete. Although this does not usually lead to any clinically significant sequelae during the period of the trial, many dogs will lose weight.

RECOMMEND DURATION OF RESTRICTED DIET TRIALS

Usually we recommend feeding an elimination diet for 6 weeks.  Many pets will show some response within 3 weeks and will not require a full 6 week test. 

To finalise the diagnosis of food allergy, animals need to be re-exposed to their original diet and a relapse recorded over a seven to ten day period.  If an animal appears to have made a spectacular recovery during the restricted diet trial, some owners are reluctant to put their pet back onto its original diet.  While it is tempting to share this view, it is important that the challenge diet is performed.  The main reason for this is to check that the response was to the diet and not a coincidence or due to any other treatment the animal may be receiving simultaneously.

LONG TERM MANAGEMENT

If a diagnosis of food allergy is eventually made then a series of sequential dietary challenges in which the animal is fed additional single protein and carbohydrate sources are used.  To begin with, the animal is placed on a restricted diet until maximal improvement has been noted,  an additional single protein or carbohydrate source is then added to the diet for 7-10 days.  If no relapse is observed, a second protein or carbohydrate source is added in place of the first once for a further 7-10 days.  This cycle is repeated until the animal has been exposed to beef, chicken , pork, lamb, turkey, fish, egg, milk bread, potato and rice.  If, at any stage, the animal relapsed, it must be placed back onto the restricted diet until maximal improvement has occurred again.  This process provides the vet and the owner with information that allows long-term dietary management of the animal to be accurately planned.  However, it takes a highly committed and motivated owner to follow these guidelines correctly and to return meaningful information.

Animals with pure food allergies can be maintained in an asymptomatic state on carefully chosen diets.  Often a suitable restricted commercial diet can be found to completely satisfy the animal's nutritional requirements.  If it is not possible to find such a diet then long- term home-cooked maintenance diets may be used.

PERSONAL  INFORMATION