Food allergy (FA) is defined as "all immune-mediated reactions following food intake," in contrast with food intolerance (FI), which is non-immune-mediated. Impairment of the mucosal barrier and loss of oral tolerance are risk factors for the development of FA. Type I, III, and IV hypersensitivity reactions are the most likely immunologic mechanisms. Food allergens are (glyco-)proteins with a molecular weight from 10-70 kDa and are resistant to treatment with heat, acid, and proteases. The exact prevalence of FA in dogs and cats remains unknown. There is no breed, sex or age predilection, although some breeds are commonly affected. Before the onset of clinical signs, the animals have been fed the offending food components for at least two years, although some animals are less than a year old. FA is a non-seasonal disease with skin and/or gastrointestinal disorders. Pruritus is the main complaint and is mostly corticoid-resistant. In 20-30% of the cases, dogs and cats have concurrent allergic diseases (atopy/flea-allergic dermatitis). A reliable diagnosis can only be made with dietary elimination-challenge trials. Provocation testing is necessary for the identification of the causative food component(s). Therapy of FA consists of avoiding the offending food component(s).

Dogs with food allergy are often treated by giving a diet with hydrolysed protein sources. Prebiotics might also be successful in prevention and treatment of allergic disease through their effect on the colonic microflora, analogous to studies on probiotics in allergic children. The present study was set up to investigate the effect of supplementing inulin (IN) to commercial hypoallergenic dog diets on apparent nutrient digestibility, faecal characteristics, haematology and Ig in dogs. Supplementation of 3 % IN did not affect faecal pH, food and water intake and urine production. Compared with the intact protein diet with a limited number of ingredients (L), the diet with a hydrolysed protein source (H) resulted in an increased water intake (P,0·001), which could be due to the osmotic effect of free amino acids. Faeces production was increased by IN due to increased faecal moisture content. Increased faeces production on the H diet was mainly due to a higher DM excretion. Subsequently, the apparent digestibility coefficient (ADC) of DM was lower in the H diet group. A similar result was noted for ADC of diethyl ether extract and crude ash. The ADC of crude protein was higher in the H diet group, whereas IN decreased the ADC of crude protein. Differences in the ADC of crude protein among the different diets disappeared after correction for a higher faecal biomass, except for the dogs fed the L þ IN diet. Total faecal IgA concentrations were lower in the H group (P, 0·05) because of lower antigenic stimulation of hydrolysed protein, which implies that hydrolysed protein is really hypoallergenic. The present study indicates that the use of hydrolysed protein diets for canine food allergy treatment can affect digestibility and that combination with IN affected apparent protein digestibility but not IgA response.

The effect on urea metabolism by the supplementation of oligofructose to a reduced protein diet was evaluated in cats by the use of labelled urea. The effect on faecal odour was also evaluated. Four cats were tested in a crossover study with two treatments: control and fructo-oligosaccharide (FOS). The FOS was supplemented at 3.11% on dry matter (DM) basis to a reduced protein diet (28.9% DM). After an adaptation period of 3 weeks, faeces and urine were collected during a 5-day collection period. Fresh faecal samples were collected for determination of odour components. On the first day of the collection period, labelled urea was injected subcutaneously. Urine production was estimated by potassium excretion. The fresh faecal samples were incubated in an air-closed recipient with two solid-phase micro extraction (SPME) fibres to bind the produced sulphur (S)-containing components. The reduced protein diet decreased plasma urea concentration but FOS supplementation had no effect. The tendency for a higher faecal output by FOS supplementation was the consequence of both an increased moisture content and faecal DM production. Supplementation of FOS showed tendencies to increase total faecal nitrogen (N) excretion and faecal (15)N excretion and tended to decrease urinary (15)N excretion. Twenty-seven different odour components were detected but were not affected by FOS supplementation.