Whole-grain cereals in dog food : Effects on metabolism and gut microbiota

During domestication from the wolf, the gastrointestinal tract in dogs adapted to a diet containing starch, which is often present in substantial amounts in commercial dog food. In humans, diets with whole grain, compared with refined, are reported to have beneficial metabolic effects, possibly through the microbiota and short-chain fatty acids (SCFA) produced during fermentation of dietary fiber by certain bacteria, e.g Prevotella. The objective of this thesis was thus to explore the effects of wholegrain cereals; wheat, oats and rye, in dog diets on metabolism, gut microbiota and SCFA. Rye is an uncommon ingredient in dog food, thus an initial study with six Beagle dogs evaluated suitable inclusion rate and effects on microbiota compared with refined wheat. In a subsequent study, 18 privately-owned dogs were fed three diets with whole grains of wheat, oats or rye in a cross-over experiment, and effects on fecal microbiota, SCFA and postprandial metabolic response were studied.Whole grain rye included at 25% of dry matter was acceptably digested and tolerated by the dogs. A 50% inclusion rate induced a significant shift in fecal microbial composition with an increase in relative abundance of Prevotella. Whole grains from wheat, oat or rye did not have differing effects on general fecal microbial composition, but microbial diversity was higher following wheat compared with rye. Bacteroides abundance was lower after rye than after wheat or oats, and inversely related to Prevotella abundance. Fecal acetate and propionate concentrations were higher after rye than after oats. The oat diet resulted in higher postprandial blood concentration of glucose, glucagon-like peptide-1 (GLP-1) and triacylglycerol compared with wheat. Fasting insulin was higher after rye than after wheat or oats. Wheat tended to result in more insulin per glucose and GLP-1 than the other two diets. Overall, the results in this thesis indicate that whole grain rye can affect dog gut microbiota composition and function in ways that could be beneficial to health. Further studies on the metabolic effects of whole grains in dog food are warranted.