@phdthesis{01J0ZKQXSZTS7GB33Z2XNX6F11,
  abstract     = {{The pet food industry has launched various types of pet food products (e.g., dry vs. wet, processed vs. raw, and other unconventional diets) to cater to the nutritional needs and preferences of dogs and cats, considering species, life stage, activity level, and size. These diets differ significantly in macronutrient content (i.e., starch, fat, protein, fibre), potentially exerting different effects on gut health. Nutritional intervention by adjusting the macronutrient content and adding dietary supplements can play a vital role in health management and targeted therapy in dogs and cats. However, limited research has been conducted on the effects of varying nutrient levels on the gut health of healthy pets, particularly the gut microbiome and metabolome. 
Therefore, the overall aim of this PhD research was to investigate the response to and relationship between nutritional intervention and the gut microbiome and metabolome in healthy adult pets. To this end, this PhD research compared the impact of high-starch, high-fat, and high-protein diets on the faecal metabolome and blood biochemistry in healthy adult dogs, and evaluated the effect of a prebiotic XOS on the faecal microbiota, fermentation end products, and serum metabolites in healthy adult cats.
In Chapter 3, we compared the inflammatory status and faecal metabolic profiles of healthy lean dogs fed a high-fat vs. a high-starch diet. The mRNA analysis did not observe any inflammatory response related changes. Results of blood biochemistry showed a tendency to increase glucose and glycine concentrations and glucose/insulin ratio in dogs in response to the high-fat diet, and an increase in non-esterified fatty acid levels as well as a tendency to increase alanine levels in dogs following the high-starch diet. Untargeted metabolomic analysis revealed 10 annotated metabolites (including e.g. L-methionine) were upregulated in dogs fed the high-starch diet, and 5 non-annotated metabolites were upregulated in dogs fed the high-fat diet. The findings suggested that a high-starch diet, compared to a high-fat diet, may promote lipid metabolism, anti-oxidative effects, protein biosynthesis and catabolism, mucosal barrier function, and immunomodulation in healthy lean dogs.
In Chapter 4, we compared the faecal metabolome of lean and obese dogs fed a high- vs. a low-protein diet. Targeted analysis demonstrated that the high-protein diet significantly increased levels of indole, spermidine and pipecolinic acid and decreased the concentration of azelaic acid, D-fructose, mannose, and galactose. Untargeted faecal metabolomics revealed distinctly different metabolomic profiles following the high-protein vs. low-protein diet, with 18 altered pathways. Results indicated that the high-protein diet influenced amino acid and lipid metabolism, potentially promoting weight loss and immune function, whereas the low-protein diet affected carbohydrate fermentation and may promote anti-oxidative function.
In Chapter 5, we evaluated the effect of two levels of XOS (0.04% and 0.40%) on the faecal microbiota, colonic fermentation, and blood metabolism in healthy adult cats. Both doses of XOS increased blood 3‐hydroxybutyryl carnitine levels and faecal Blautia, Clostridium XI, and Collinsella abundance, but decreased blood hexadecanedioyl carnitine levels and faecal abundance of Megasphaera and Bifidobacterium. The 0.04% XOS supplement increased faecal pH and bacterial abundance of Streptococcus and Lactobacillus, decreased the blood glutaryl carnitine concentration and faecal Catenibacterium abundance. The 0.40% XOS supplement showed increased trends in the α-diversity (Shannon and inverse Simpson index) and higher species richness, and an increased bacterial abundance of Subdoligranulum, Ruminococcaceae genus (unassigned genus), Erysipelotrichaceae genus, and Lachnospiraceae. These findings demonstrated that XOS could benefit feline gut health by altering the microbiota, and its associated effects, dependant on the dose. The higher‐dose XOS increased bacterial populations that may promote intestinal fermentation, while the lower dose altered populations of carbohydrate‐metabolic microbiota, and possibly modulates host metabolism. 
The main conclusion of this PhD research is that nutritional interventions by altered macronutrient composition and prebiotic supplementation influenced the gut microbiome and metabolome in healthy adult dogs and cats, while isoenergetic exchange of dietary macronutrients did not show negative health effects on the gut of healthy dogs. Future investigations on the nutritional interventions and gut health will focus on the time/dose effects, the conjoint analysis of microbiome and metabolome, more diverse food ingredients and sources, and different health status and life stages of animals.}},
  author       = {{Lyu, Yang}},
  keywords     = {{microbiota,metabolome,gut health,diet,metabolism,dogs and cats,nutritional intervention}},
  language     = {{eng}},
  pages        = {{204}},
  publisher    = {{Ghent University. Faculty of Veterinary Medicine}},
  school       = {{Ghent University}},
  title        = {{Nutritional intervention and gastrointestinal microbiome and metabolome in dogs and cats}},
  year         = {{2024}},
}