Understanding the impact of using edible species of microalgae as dietary supplement on palatability, digestibility, faecal metabolites and microbiota in healthy dogs
This study aimed to evaluate the effects of different levels of dietary inclusion of edible microalgae species (Tetradesmus obliquus, Chlorella vulgaris, and Nannochloropsis oceanica) on apparent total tract digestibility of nutrients, metabolisable energy (ME) content, diet palatability, and faecal metabolites and microbiota of dogs. A commercial extruded complete diet for adult dogs without the inclusion of microalgae was used as a reference diet in all trials. Three trials were designed according to two Latin squares 3 x 3, with six animals, three experimental periods, and three dietary inclusion levels of each microalgae species (0.5%, 1.0%, and 1.5% in substitution of the reference diet). Twelve adult dogs were used for the palatability tests to compare the reference diet with diet with 1.5% dietary inclusion of each microalgae species. Dietary inclusion of microalgae studied up to 1.5% did not promote evident changes in the chemical composition of diets and kept unaffected food intake and faecal output. Comparing with the reference diet, the dietary inclusion of T. obliquus and N. oceanica did not significantly affect diet digestibility, but inclusion of C. vulgaris increased crude protein digestibility. Dietary metabolisable energy content was unaffected by microalgae supplementation. Frequency of defecation decreased with the dietary inclusion of T. obliquus and C. vulgaris. Dry matter content of faeces was higher with N. oceanica inclusion over the reference diet, and T. obliquus decreased the faecal consistency score. First diet approached or tasted were not significantly affected by microalgae inclusion, but dogs consumed significantly more of the reference diet. Regardless of the species, microalgae inclusion decreased faecal pH and increased total volatile fatty acids production and acetate concentration, whereas C. vulgaris and N. oceanica increased propionate, butyrate and branched-chain fatty acids concentrations. Microbiota composition was affected by microalgae inclusion but not by the level of inclusion. Feeding dogs with algae-supplemented diets benefit microbial genus associated with gut health and activation of the immune system. Overall, the results support the potential of T. obliquus, C. vulgaris and N. oceanica as sustainable functional foods for dog feeding.