Dietary Tryptophan Requirements in Adult Dogs and How Optimization of the Tryptophan to Large Neutral Amino Acid Ratio Affects the Metabolism and Gut Health in Actively Training Sled Dogs
Exercise improves the health of dogs; although, extreme exertion experienced by sled dogs may lead to variable metabolic and gastrointestinal outcomes. Nutritional solutions can reduce the prevalence of these disturbances, but a deeper understanding of sled dog nutritional programs is warranted to ensure appropriate gaps in research are targeted. Supplementation of tryptophan, an indispensable amino acid for dogs, has been explored as a means to increase serotonin, a neurotransmitter involved in central and enteric nervous system function; however, there are no empirical data to support current regulatory recommendations of dietary tryptophan for adult dogs. The objectives of this thesis were to 1) critically review aspects of sporting dog nutrition, methods of estimating amino acid requirements, and tryptophan metabolism, 2) evaluate current sled dog nutritional programs, 3) estimate tryptophan requirements in adult dogs, and 4) apply those estimations via optimizing the dietary tryptophan to large neutral amino acid ratio for actively training sled dogs, with the goal of improving metabolic and gastrointestinal outcomes. Survey- based data pertaining to sled dog nutritional management revealed the need for improvements in nutrient provision, particularly protein, in order to reduce the perceived necessity of (and risks associated with) raw meat supplementation and formulation of homemade diets without scientific or clinical consideration. Using indicator amino acid oxidation, tryptophan requirements were estimated for small (miniature dachshunds), medium (beagles), and large breed (Labrador retrievers) dogs, and all estimates were higher than current regulatory recommendations. Effects of supplemental dietary tryptophan and incremental exercise on metabolic and gastrointestinal outcomes were then investigated using Siberian huskies and a diet formulated to achieve the highest tryptophan to large neutral amino acid ratio used when feeding adult dogs to their tryptophan requirements. Tryptophan supplementation improved serotonin status and fecal quality without affecting body composition in actively training dogs, demonstrating the potential benefits of tryptophan supplementation. Specifically, tryptophan supplementation may help to support gastrointestinal function in sporting dogs under stressful conditions (e.g. intensive exercise) without compromising athletic performance. Further research is warranted to investigate effects of secondary metabolic pathways and factors that may increase metabolic demand on indispensable amino acid requirements and supplementation.