Vet Watch, April 19

Was it something I ate?

Last month I had a bit of a chat about some allergies that plague our pets. I made a reference at some point about food allergies, so I thought I would elaborate a little this month.

Food allergies (FA) generally manifest as skin disease. Allergic skin disease is common in dogs and cats, but there are some differences in the most common ways that food allergies appear in different species.

Generally food allergies in dogs occur at at a younger age than in cats. About 50% of food allergy occurs in canine patients less than one year old. In cats most FA is in patients older than six. Mostly it is non-seasonal, although it may wax and wane if combined with other conditions like atopy.

It’s usually not obvious what has kicked off the allergy. In cats there is some indication that the itch associated with FA is worse about the neck, face and ears, but this isn’t consistent enough to be diagnostic. In dogs sometimes the only sign is persistent perineal itch (an itchy bum) that’s often mistaken for anal gland problems. Ear infections are found in probably 80% of patients, and sometimes it’s the only sign. Often patients with FA also have gastrointestinal signs such as increased stool frequency of soft stools, a cross-over with dietary sensitivity. 

There’s no reliable scientific evidence of preservatives or food colourings causing allergies, in spite of what facebook may say. Similarly it makes no difference if the food is organic or not. That’s just marketing. Also good marketing but bad science, is blaming FA on grains and in particular wheat. It’s not impossible, but its a very minor contributor to the rogues gallery of allergens. Also, gluten intolerance in our pets is so rare as to be virtually non existent.

The culprit almost invariably is an animal protein. And it doesn’t matter particularly what animal protein it is. All that’s required is regular exposure and a pre-disposition in that individual. The most common proteins causing FA are beef, chicken and lamb. However, if people regularly fed soy-protein and aardvark, to their pets, then these proteins would take the number one spot on the allergen list instead. 

The only effective way to diagnose FA, and the gold standard, is a so-called unique-protein diet (or elimination diet), strictly and exclusively adhered to, for 8 to 12 weeks (although sometimes there’s a response by 3 weeks). During this time patients eat only a single type of protein that they have never eaten before.

If things go well (i.e. no more itch) then the patient is challenged with the old diet in its entirety. Mostly a pet with FA will start itching again within 7 days. Then you have to restart the elimination diet and go through the process again. It’s a bit of a pain and it takes a while. But it’s necessary and may make the difference between a lifetime of misery for your pet, and ongoing frustration/costs for the owner. 

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