The prevalence of dog obesity is increasing and a better understanding of the metabolism of overweight dogs is needed to improve obesity prevention and treatment. This study aim to detect and quantify plasma metabolites during a feed challenge-test in dogs and to identify alterations in the metabolism related to overweight. Twenty-eight healthy intact male Labrador retriever dogs were included, 12 of which were classified as lean (body condition score (BCS) 4–5 on a 9-point scale) and 16 as overweight (BCS 6–8). After overnight fasting, plasma samples were collected and dogs were fed a high-fat meal. Postprandial plasma samples were collected hourly for 4 hours. Nuclear magnetic resonance (NMR) was conducted and 41 plasma metabolites were statistically evaluated. The results showed that all postprandial time points differed from the fasting time point in multivariate discriminant analysis (cross-validated ANOVA: p=0.00014). Eleven specific metabolites with peak concentrations mainly at 2 or 3 hours postprandially contributed to the separations. Carnitine was identified as a metabolite related to overweight at all time points in stepwise logistic regression analysis (p=0.03) and overweight dogs had lower carnitine response in a mixed model repeated measures analysis (p=0.005). Notably, the fasting carnitine concentration in overweight dogs (mean±SD, 9.4±4.2 mM) was very close to a proposed reference limit for carnitine deficiency. These findings demonstrate that NMR is suitable for metabolic evaluations in feed-challenges in dogs. The lowered carnitine concentration in overweight dogs warrants further investigation as it could indicate carnitine deficiency and an altered lipid metabolism in overweight dogs.

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