Raw meat-based diets (RMBDs) are typically fed to exotic carnivores managed in zoological institutions and are gaining in popularity as dietary options for pet dogs. Current research themes of RMBDs for zoo carnivores have centered around utilization in exotic felid species with a paucity of data obtained from exotic canids. In addition, current research themes of RMBDs for domestic dogs have centered around microbial contamination. Conducting nutrition-related research in exotic canids is often limited because animals are group-housed, preventing accurate individual feed intake and fecal output collection. Due to functional and anatomical similarities between digestive systems of domestic dogs with their wild counterparts, dogs may serve as an experimental model for nutrition studies for certain exotic canid species.

The overall objectives of this research were to evaluate four commercially manufactured RMBDs formulated for zoological carnivores using domestic dogs as a model for exotic canids and to evaluate microbial risk to humans and canine health implications beyond digestibility. We hypothesize all RMBDs: 1.) evaluated would be highly digestible in domestic dogs, 2.) microbial risk to humans would be low, and 3.) there would be no adverse implications on canine health as a result of feeding RMBDs.

Overall, nutrients in RMBDs were highly digested by domestic dogs and diets did not result in clinical signs of gastrointestinal upset/distress. Further, RMBDs did not negatively influence general health status in dogs as measured by serum chemistry, electrolytes, complete blood count (CBC), and histology of gastrointestinal tract and associated tissues. Ussing chamber evaluation of intestinal integrity and barrier function indicated possible benefit of feeding RMBDs to dogs.

Our first aim was to evaluate diet composition, apparent total tract macronutrient and energy digestibility, feed intake, fecal output, and microbial presence of four commercially-manufactured RMBDs for zoological carnivores fed to domestic dogs. Diets varied in protein source including horse (Horse), pork (Pork) and two beef-based diets (Beef 1 and Beef 2). Our results indicated that diets were comparable in nutrient and energy composition and apparent total tract digestibility when fed to domestic dogs (n=4). Treatment nutrient concentrations ranged for dry matter (DM) (32.2 – 36.2%), organic matter (OM) (91.1 – 94.9%), crude protein (CP) (50.3 – 61.7%), fat (25.1 – 38.3%), and gross energy (GE) (5.8 – 6.4 kcal/g). Digestibility of nutrients and energy ranged from 83.3 – 92.4%, 88.4 – 95.3%, 93.8 – 97.7%, 94.9 – 98.2%, and 91.3 – 95.5% for DM, OM, CP, fat, and energy, respectively. Fecal chemical composition, specifically fat on a dry matter basis (DMB), differed markedly for dogs consuming one of the beef diets (Beef 2). Dogs fed Beef 2 had greater (P<0.05) concentrations of fat in feces (21.5%) compared to 2.9, 6.1, and 6.3% for dogs fed Horse, Pork, and Beef 1, respectively. Despite the large fecal fat concentration, dogs fed Beef 2 diet had greater (P<0.05) digestibility of DM (92.4%), OM (95.3%), CP (97.7%), and GE (95.5%) but lesser (P<0.05) digestibility of fat (94.9%) compared with all other diets evaluated. Additional digestibility differences were few. Feces were scored using the following scale: 1 = very hard, dry feces to 7 = watery diarrhea (Nestlà  à © Purina). Fecal scores were lower (P<0.05) when dogs were fed Horse (1.2) and Beef 2 (1.9) diets compared to Pork (2.7) and Beef 1 (3.1) diets. Detection of Salmonella spp. in diet and saliva samples was non-existent and only 5.6% (n=2/36) of fecal samples were Salmonella spp. positive. Detection of generic E. coli was determined in 12.5% (n=2/16) and 5.6% (n=2/36) of diet and saliva samples, respectively.

Our second aim was to compare gastrointestinal histology, intestinal transepithelial electrical resistance (TER), and intestinal macromolecule permeability between domestic dogs fed commercial extruded- versus RMBDs. No differences were observed in gastrointestinal histology between dietary treatment groups. TER and macromolecule permeability data were highly variable and statistical analyses were not performed due to low sample size. Numerical increases in apparent permeability coefficient (Papp) were observed in extruded-fed dogs indicating increased macromolecule permeability that is suggestive of decreased intestinal integrity and barrier function. These results indicate potential improvements in intestinal barrier function when dogs were fed RMBDs using a novel technique; however, further evaluation should be considered with a larger sample size.

This research demonstrates that RMBDs varying in protein source and ingredients can be effectively utilized by domestic dogs and potentially exotic canids. While these experiments evaluated four commercial products manufactured for exotic carnivores in domestic dogs, further research should evaluate direct comparisons between digestive efficiencies of domestic dogs compared to various exotic canid species. Our research also indicates that human exposure to pathogens associated with feeding RMBDs to dogs is possible but risk appears low based on presence of measured microbes. Additionally, this research indicates value in the use of gastrointestinal histology and Ussing chamber evaluation of intestinal integrity and barrier function as novel approaches for determining health effects beyond nutrient digestibility of various diets in domestic dogs.