PSIX-3 Microbial protein inclusion in adult dog diets and the impact on digestibility, stool quality, and palatability.

Abstract Microbial protein (Methylococcus capsulatus; MP) has been developed as a novel sustainable protein source due to its low land and water usage. In this study, we evaluated the impact of MP dietary inclusion on nutrient digestibility, stool quality, and palatability in adult dogs. The high protein, chicken-based control diet was formulated to meet AAFCO Adult Maintenance ranges. The test diets matched the macronutrients of the control, but included MP at 2.5% or 5%, substituting pea protein. The study was approved and followed by the facility’s Institutional Animal Care and Use Committee. A 2-bowl preference test was performed over a 2-day period (n=30 each) to measure intake ratios (IR) between the control, 2.5%, and 5% MP diets. Evaluation of total tract nutrient digestibility (N=6 per diet) was conducted using a 10-day protocol consisting of 5 days of diet feeding acclimation followed by a 5-day period of total fecal collection. Stool quality was assessed by scoring fecal samples using a 1–5-point scale, where 1= nonformed/ diarrhea and 5=hard formed. Data were analyzed by mixed procedure of SAS 9.4 (SAS Inst. Inc., Gary, NC), with treatment as the fixed effect. An LSMEANS statement was used to calculate the least square means for each treatment with Tukey-Kramer adjustment for multiple comparison among treatments. No differences were observed between diets for dry matter and protein digestibility (>79% and > 83% avg, respectively; P > 0.10). However, we observed a slight increase (P < 0.05) in fat digestibility for 5% MP (94.8%) vs control (92.7%) and 2.5% MP (93.1%). Stool scores were similar between groups (all averages between 3.3-3.5). The 2.5% MP diet had similar palatability relative to control (IR=56:44, 2.5% MP vs. control; P > 0.10). However, we observed that 5% MP inclusion led to reduced palatability compared to control (72:28, 5% MP vs. control P < 0.05), and 2.5% was preferred vs. 5% (69:31, 2.5% MP vs. 5% MP; P < 0.05). In sum, digestibility and stool quality were not greatly influenced by MP inclusion of up to 5%, but palatability might be impacted by this novel protein at higher inclusion levels in adult dog diets.