Middleton, R.P et al.
2017
Journal of Nutrition and metabolism

Small dogs exhibited a lower antioxidant status and variations in circulating amino acids. Some of these differences in amino acids may be linked to variations in microflora. Furthermore, the analysis of metabolites and clinical parameters in small dogs revealed a network that is closely associated with kidney function.

This study by Middleton et al. explores the metabolic, clinical, and microbiota differences between small and large dogs, highlighting the physiological and biochemical variations associated with body size. Using a cohort of 83 dogs from seven breeds, all fed an identical diet, the researchers applied metabolomics, clinical chemistry analysis, and microbiota profiling to characterise the impact of body size on metabolism. They identified 449 metabolites, 16 clinical parameters, and six bacterial genera that significantly differed between small and large dogs. Key findings included lower antioxidant status in small dogs, variations in circulating amino acids influenced by gut microbiota, and metabolic markers linked to kidney function. Notably, small dogs exhibited reduced levels of glutathione, bilirubin, and urate, suggesting a different oxidative balance compared to larger counterparts. Amino acid metabolism was also distinct, with lower levels of phenylalanine and tyrosine in small dogs, which correlated with increased microbial fermentation.
Furthermore, the study identified a metabolic module strongly associated with kidney function, with small dogs showing significant differences in creatinine and homocitrulline levels. The gut microbiota composition varied significantly, with small dogs harbouring higher levels of Bacteroides and Faecalibacterium, while larger dogs exhibited increased Collinsella and Lactobacillus. These findings suggest that body size in dogs influences metabolic pathways that affect oxidative stress, protein metabolism, and renal function. This research provides valuable insights into breed-specific nutritional and health considerations, emphasising the need for tailored dietary interventions to optimise canine health across different body sizes.