Apparent total-tract macronutrient digestibility, serum chemistry, urinalysis, and fecal characteristics, metabolites and microbiota of adult dogs fed extruded, mildly cooked, and raw diets1

Abstract

Despite their popularity, little research has been performed on lightly cooked and raw diet formats for pets. Therefore, the objective of this study was to determine the apparent total-tract macronutrient digestibility (ATTD); fecal characteristics, metabolites, and microbiota; serum chemistry metabolites; urinalysis; and voluntary physical activity levels of adult dogs fed commercial diets differing in processing type. The diets included: 1) extruded dry kibble (EXT) diet; 2) high-moisture roasted refrigerated (RR) diet; 3) high-moisture grain-free roasted refrigerated (GFRR) diet; and 4) raw (RAW) diet. Eight dogs (mean age = 3.6; mean BW = 13.0 kg) were used in a replicated 4 × 4 Latin square design. Each period consisted of 28 d, with a 14-d adaptation phase followed by a 7-d phase for measuring voluntary physical activity, 1-d adaptation phase to metabolic cages, 5-d phase for fecal and urine collection, and 1 d for blood collection. Except for microbiota, all data were analyzed statistically by mixed models using SAS. Microbiota data were analyzed using Quantitative Insights Into Microbial Ecology (QIIME) and Statistical Analyses of Metagenomic Profiles (STAMP) software. Many differences in digestibility were observed, including greater (P < 0.05) ATTD of CP and fat in dogs fed GFRR and RR than dogs fed EXT. Dogs fed RAW had the lowest fecal pH and DM %, but fecal scores were not affected. Dogs fed RR had higher (P < 0.05) fecal indole and total phenol and indole concentrations than dogs fed the other diets. Dogs fed RAW had a higher (P < 0.05) fecal ammonia concentration than dogs fed the other diets. Fecal microbial diversity was altered by diet, with dogs fed GFRR and RAW having reduced species richness than dogs fed EXT. Dogs fed RR, GFRR, or RAW had lower (P < 0.05) Actinobacteria and higher (P < 0.05) Fusobacteria than dogs fed EXT. Dogs fed RAW or GFRR had higher (P < 0.05) Proteobacteria than dogs fed EXT or RR. Dogs fed RAW had higher (P < 0.05) Bacteroidetes and lower (P < 0.05) Firmicutes than dogs fed EXT. Serum triglycerides were within reference ranges, but greater (P < 0.05) in dogs fed EXT than dogs fed GFRR and RAW. All diets were well tolerated and dogs remained healthy throughout the study. In conclusion, the lightly cooked and raw diets tested were highly palatable, highly digestible, reduced blood triglycerides, maintained fecal quality and serum chemistry, and modified the fecal microbial community of healthy adult dogs.

Keywords: canine nutrition; diet processing; gastrointestinal microbiome; nutrient digestibility.

Figure 1.

Fecal microbial communities of dogs fed extruded, mildly cooked, and raw diets. (A) Alpha diversity measures suggested that species richness was lower (P < 0.05) in dogs fed the high-moisture grain-free roasted refrigerated (GFRR) diet or raw (RAW) diet than dogs fed the extruded dry kibble (EXT) diet. Principal coordinates analysis plots of unweighted (B) UniFrac distances of fecal microbial communities performed on the 97% OTU abundance matrix tended to reveal a separation (P = 0.07) between dogs fed GFRR or RAW from dogs fed EXT. Principal coordinates analysis plots of weighted (C) UniFrac distances of fecal microbial communities performed on the 97% OTU abundance matrix tended to reveal a separation (P = 0.07) between dogs fed the high-moisture roasted refrigerated (RR) diet or RAW from dogs fed EXT. Each dot represents a sample collected from each dog (n = 8/treatment). OTU = operational taxonomic units.

Figure 2.

Relative abundances of differentially abundant microbial phyla (P < 0.05) in feces of dogs fed an extruded dry kibble (EXT), high-moisture roasted refrigerated (RR), high-moisture grain-free roasted refrigerated (GFRR), or raw (RAW) diet (n = 8/treatment). False discovery rate corrected P values using the Benjamini–Hochberg method were calculated using Statistical Analyses of Metagenomic Profiles (STAMP) software, using ANOVA and a Tukey adjustment. Each box represents the 25% and 75% percentiles; error bars indicate 95% confidence interval of median.

Figure 3.

Relative abundances of differentially abundant microbial genera (P < 0.05) in feces of dogs fed an extruded dry kibble (EXT), high-moisture roasted refrigerated (RR), high-moisture grain-free roasted refrigerated (GFRR), or raw (RAW) diet (n = 8/treatment). False discovery rate corrected P values using the Benjamini–Hochberg method were calculated using Statistical Analyses of Metagenomic Profiles (STAMP) software, using ANOVA and a Tukey adjustment. Each box represents the 25% and 75% percentiles; error bars indicate 95% confidence interval of median.