From Chihuahua to Saint-Bernard: how did digestion and microbiota evolve with dog sizes

Abstract

Health and well-being of dogs are of paramount importance to their owners. Digestion plays a key role in dog health, involving physicochemical, mechanical and microbial actors. However, decades of breeding selection led to various dog sizes associated with different digestive physiology and disease sensitivity. Developing new products requires the consideration of all the multi-faceted aspects of canine digestion, the evaluation of food digestibility, drug release and absorption in the gut. This review paper provides an exhaustive literature survey on canine digestive physiology, focusing on size effect on anatomy and digestive parameters, with graphical representation of data classified as "small", "medium" and "large" dogs. Despite the huge variability between protocols and animals, interesting size effects on gastrointestinal physiology were highlighted, mainly related to the colonic compartment. Colonic measurements, transit time permeability, fibre degradation, faecal short-chain fatty acid concentration and faecal water content increase while faecal bile acid concentration decreases with body size. A negative correlation between body weight and Proteobacteria relative abundance was observed suggesting an effect of dog body size on faecal microbiota. This paper gathers helpful in vivo data for academics and industrials and supports the development of new food and pharma products to move towards canine personalized nutrition and health.

Keywords: canine; digestive physiology; gut microbiota; petfood; veterinary products.

Figure 1

Impact of dog sizes on pH values in all digestive compartments. Results from studies measuring in dog's pH values in the stomach (under fasted or fed conditions), small intestine, large intestine and faeces are presented. Small dogs are plotted in green, medium dogs in yellow, large dogs in orange and unclassified dogs in grey. Raw data were pooled in “all” group (in black). Calculated median values are in italic bold, values for a single point in italic. Black bars represent 95% confidence intervals. The number of dogs involved in studies is indicated as “N=”

Figure 2

Impact of dog sizes on faecal bile acids. Results from studies in dog faeces quantifying total bile acids (BA) are represented in (a), further separated into primary (blue crosses) and secondary BA (red crosses) in (b). Detailed composition in cholic acid (CA), chenodeoxycholic acid (CDCA), lithocholic acid (LCA) and deoxycholic acid (DCA) is shown in (c). The same caption as used in Fig. 1 was applied

Figure 3

Diet composition and impact of dog sizes on total apparent digestibility. Nutritional composition of dry food diet used in canine studies is represented in (a). Results from studies investigating in dogs' total digestibility of proteins, lipids and fibres are presented in (b), (c) and (d), respectively. The same caption as used in Fig. 1 was applied

Figure 4

Impact of dog sizes on gastrointestinal transit time. Results from studies in dogs evaluating gastric emptying time (GET) under fasted or fed status, small intestinal transit time (SITT), large intestinal transit time (LITT) and total transit time (TTT) are represented. The same caption as used in Fig. 1 was applied

Figure 5

Variations in gut microbiota composition along the canine digestive tract and impact of dog sizes. Main bacteria populations found in the different compartments of the dog gastrointestinal tract are represented in (a). Bacteria counts are expressed in colony forming units (CFU) per gram of digestive content. Results from studies exploring by 16S rRNA Illumina sequencing canine microbiota composition (regardless of dog size) in the different digestive compartments are presented in (b). Influence of dog sizes on faecal microbiota composition at the phylum level is shown in (c) and corresponding Shannon index in (d). Canine main phyla are Firmicutes (Firm), Bacteroidetes (Bact), Fusobacteria (Fuso), Proteobacteria (Proteo) and Actinobacteria (Actino). The same caption as used in Fig. 1 was applied

Figure 6

Impact of dog sizes on faecal microbial products production. Results from studies in dogs measuring total faecal major short-chain fatty acids (SCFA, i.e. acetate, propionate and butyrate) are presented in (a) and detailed in (b). Similarly, influence of dog size on major branched-chain fatty acids production (BCFA, i.e. isobutyrate, isovalerate and valerate) is shown in (c) and detailed in (d). Effect of dog size on other microbial metabolites are presented in (e) for phenols and indoles and (f) for ammonia. The same caption as used in Fig. 1 was applied

Figure 7

Overview of the impact of dog sizes on digestive physiology and faecal microbiota composition and activity. Key parameters of the oral, gastric, intestinal and colonic compartments from the canine digestive tract are summarized. Specified values were obtained from reports comparing in a same study the results obtained for small and large dogs. Lack of data are represented by “?”, BA: bile acid, SCFA: short chain fatty acids. *: Lactulose/L-rhamnose ratio, **: Lactulose/sucralose ratio