Squid meal and shrimp hydrolysate as novel protein sources for dog food

The world's growing pet population is raising sustainability and environmental concerns for the pet food industry. Using protein-rich by-products from aquatic sources might contribute to mitigating negative environmental effects, decreasing waste, and improving economic efficiency. The present study aimed to evaluate two marine by-products, squid meal and shrimp hydrolysate, as novel protein sources for dog feeding. Along with the analysis of their chemical composition and antioxidant activity, palatability was evaluated through two-bowl tests comparing a commercial diet (basal diet) and diets with the inclusion of 150 g kg-1 of squid meal or shrimp hydrolysate. Two in vivo digestibility trials were conducted. Three experimental periods (10 days each) and three dietary inclusion levels (50, 100 and 150 g kg-1) of squid meal or shrimp hydrolysate in place of basal diet were performed to evaluate the effect of inclusion level on apparent total tract digestibility (ATTD), metabolizable energy (ME) content, fecal characteristics, metabolites, and microbiota in adult Beagle dogs. Both protein sources presented higher crude protein (CP) and methionine contents than ingredients traditionally used in dog food formulation. Shrimp hydrolysate extracts showed higher antioxidant activity than squid meal. First approach and taste were not affected by the inclusion of protein sources, but animals showed a preference for the basal diet. Effects on nutrient intake reflected the chemical composition of diets, as fecal output and characteristics were not affected by the inclusion of increasing levels of both protein sources. The higher ATTD of DM, most nutrients and energy of diets with the inclusion of both by-products when compared to the basal diet, suggests their high potential to be included in highly digestible diets for dogs. Fecal metabolites were not affected by the inclusion level of protein sources, but when compared to the basal diet, the inclusion of squid meal decreased butyrate concentration and the inclusion of shrimp hydrolysate increased volatile fatty acids, except butyrate. Fecal microbiota of dogs was not affected by squid meal inclusion, whereas inclusion levels of shrimp hydrolysate significantly affected abundances of Oscillospiraceae (UCG-005), Firmicutes and Lactobacillus. Overall, results suggest that squid meal and shrimp hydrolysate constitute novel and promising protein sources for dog food, but further research is needed to fully evaluate their functional value.