Analysis of Intestinal Microbiota and Metabolic Pathways before and after a 2-Month-Long Hydrolyzed Fish and Rice Starch Hypoallergenic Diet Trial in Pruritic Dogs

SIMPLE SUMMARY: Intestinal microbiota alterations were described in allergic people, which may improve with special diets, leading to decrease in allergy symptoms. Farmina Ultra Hypo (FUH) is a hypoallergenic diet able to improve pruritus and skin lesions in allergic dogs. Study objectives were to determine intestinal microbiota alterations in skin allergic dogs and the effect of feeding FUH. Forty skin allergic dogs were fed FUH for 8 weeks and feces were collected before and after the trial. Dogs clinically improving with the diet were considered food allergic, while those not improving were considered allergic to the environment (affected by atopic dermatitis). As previously reported, the gut microbiota in all dogs was dominated by Bacteroidota, Fusobacteriota, Firmicutes and Proteobacteria, albeit with large variations between dogs and with some changes after the diet. In general, bacteria producing beneficial short-chain fatty acids were increased in all samples. Dogs affected with atopic dermatitis showed different pre-and post-diet microbiota patterns to food allergic dogs. The number of bacterial types was increased after the diet only in food allergic dogs. Changes in metabolic pathways were observed mainly in atopic dermatitis dogs. FUH may be able to improve intestinal microbiota and thus clinical signs of skin allergy. ABSTRACT: Intestinal microbiota alterations were described in allergic individuals and may improve with diets. Farmina Ultra Hypo (FUH), a hydrolyzed fish/rice starch hypoallergenic diet, is able to improve clinical signs in allergic dogs. Study objectives were to determine microbiota differences in allergic dogs before and after feeding with FUH for eight weeks. Forty skin allergic dogs were evaluated clinically before and after the diet. Unresponsive dogs were classified as canine atopic dermatitis (CAD); responsive dogs relapsing after challenge with previous foods were classified as being food reactive (AFR), and those not relapsing as doubtful (D). Sequencing of feces collected pre- and post-diet was performed, with comparisons between and within groups, pre- and post-diet, and correlations to possible altered metabolic pathways were sought. Microbiota in all dogs was dominated by Bacteroidota, Fusobacteriota, Firmicutes and Proteobacteria, albeit with large interindividual variations and with some prevalence changes after the diet. In general, bacteria producing short-chain fatty acids were increased in all samples. CAD dogs showed pre-and post-diet microbiota patterns different from the other two groups. Bacteria taxa were enriched post-diet only in the AFR group. Changes in metabolic pathways were observed mainly in the CAD group. FUH may be able to improve intestinal microbiota and thus clinical signs of skin allergy.