280. Evaluating the Effect of a Dietary Yeast Product on Thermoregulatory, Digestive, and Metabolic Responses in Exercising Dogs.

Abstract Yeast-derived products, including yeast autolysate from Saccharomyces cerevisiae, contain bioactive compounds such as β-glucans and mannan-oligosaccharides that may support gut health and physiological resilience during stress. Exercise, however, may elicit thermoregulatory and metabolic strain in athletic dogs, particularly during repeated training or warm environmental conditions. Therefore, the objective of this study was to evaluate the effects of dietary yeast supplementation on body composition and gross thermoregulatory measures during a 10-week training period in working sled dogs. Twenty-two client-owned Siberian huskies and 2 Alaskan huskies (13 females: 1 intact, 12 spayed; 11 males: 5 intact, 6 neutered) with a mean (±SD) age of 5.6 ± 2.7 yr, a body condition score of 4-6 on a nine-point scale, and body weight of 21.9 ± 2.7 kg were used. Dogs were grouped and then randomly assigned to either a control (n = 12) group, which received only a dry extruded kibble, or a treatment (n = 12) group that received the same diet top-dressed with yeast supplement at 100 mg/kg BW. Standardized exercise challenges were conducted at week -1, 1, 5, and 10, where rectal temperature (RT) was measured pre-run and at 0, 2, 5, 10, and 15 min post-run. Heart rate (HR) and respiratory rate (RR) were measured before, during, and after exercise on the same weeks. Body composition was assessed pre- and post-study by dual-energy X-ray absorptiometry to assess changes in lean and fat mass. Data were analyzed using PROC GLIMMIX in SAS, with dietary group (DG), week, training intensity and sex included as fixed effects, and dog as a random effect. Significance was declared at P < 0.05. Dietary group and DG × week did not affect RT, HR, or RR at any point throughout the trial period (P > 0.05). Week effects were observed for RT immediately post-run (P = 0.026), 2 min post-run (P = 0.047), and 5 min post-run (P = 0.047), with week 5 lower than week -1, 1, and 10. Week effects were also observed for preHR (P = 0.002), postHR (P < 0.001), preRR (P = 0.026), and postRR (P = 0.017), with a decrease observed at weeks 5 and 10 compared to weeks -1 and 1, with weeks -1 and 1 not differing. Dietary group and DG × week did not affect fat mass or lean body mass (P > 0.05); however, fat mass decreased (P = 0.001), and lean body mass increased (P < 0.001) during the trial period. These results suggest that yeast supplementation at 100 mg/kg BW did not alter gross physiological or body composition responses during moderate exercise training, while week effects indicate that progressive exercise was the primary driver of observed physiological change.