A randomized, double-blinded crossover trial testing the benefit of two hydrolysed poultry-based commercial diets for dogs with spontaneous pruritic chicken allergy

Background - Hydrolysed protein diets are used to diagnose and treat dogs with cutaneous adverse food reactions (CAFR). Little is known about what proportion of dogs hypersensitive to the native protein would react to its hydrolysed form. Objectives - To determine the clinical allergenicity of hydrolysed poultry feather (RCU) and chicken liver diets (HZD) in dogs with chicken induced CAFR. Methods - In this randomized, double-blinded, crossover trial, ten dogs with chicken induced CAFR were selected after a positive oral challenge to chicken meat and a negative one to corn. Test diets were fed for 14 days separated by a 14 day wash-out period. Owners rated pruritus daily with a Visual Analog Scale (PVAS). The challenge was ended if a flare in pruritus occurred (i.e. PVAS >= 5/10). Results - The median PVAS scores before feeding RCU and HZD were 0.9 and 1.7, respectively (Wilcoxon signed rank test, P = 0.46). Pruritus scores increased significantly after feeding HZD (Friedman's test, P < 0.001) but not after feeding RCU (P = 0.895). None of the dogs fed RCU, but four dogs fed HZD (40%), were withdrawn after a flare in pruritus developed (Fisher's test, P = 0.04). The maximal PVAS score was significantly higher after HZD (median: 4.7) compared to RCU (2.5) (Wilcoxon signed rank test, P = 0.01). One dog in each group was withdrawn due to diarrhoea. Conclusions - The hydrolysed poultry feather diet did not induce pruritus flares in dogs allergic to chicken in contrast to the hydrolysed chicken liver diet that led to pruritus flares in 40% of these dogs.