Determination of nutrients digestibility in commercial dry dog food containing various protein sources

This study evaluated the nutritional adequacy and digestibility of commercial dry dog foods formulated with different protein sources (animal versus plant) and market tiers (premium versus economy). Eight commercial dog foods were analyzed for nutrient composition and amino acid profiles using proximate analysis and high-performance liquid chromatography (HPLC). Of these, four representative products were selected to assess digestibility through in vivo total fecal collection in Beagle dogs and in vitro digestion assays. All products exceeded 18% crude protein (the minimum crude protein requirement by AAFCO). However, deficiencies were examined in essential amino acids, particularly leucine, isoleucine, methionine, lysine, tryptophan, valine and phenylalanine. Animal protein dog foods showed higher digestibility, with significantly different in digestibility coefficients for dry matter 80.3–85.3%, crude protein 84.7–85.5%, ether extract 97.6–98.2%, and gross energy 87.0–90.6% compared to plant protein diets dry matter 72.6–82.6%, crude protein 79.3–79.5%, ether extract 86.8–92.4%, gross energy 76.8–84.4%. Premium pricing did not reliably correlate with better digestibility, certain economical animal protein diets demonstrated comparable nutrients absorption compared to premium products. In vitro digestibility overestimated by 4-8% in vivo trials, highlighting limitations in laboratory predictions. This study emphasizes protein source and formulation as critical determinants of nutritional adequacy, challenging consumer assumptions about product quality based solely on market tier. Comprehensive nutritional quantity and quality evaluations are essential for accurately assessing dog food quality.