A simple method to predict the apparent total tract digestibility of crude protein of adult dogs

Crude protein (CP) levels in and digestibility of dog food are important for evaluating the food quality. Moreover, CP digestibility data offer nutrient bioavailability information to consumers to assess food quality and reliability that are valuable from an animal health and welfare perspective. However, evaluating the nutritional value of ingredients for companion animals requires abundant time, financial investment, and animal experiments. This entails practical challenges in product development, quality control, and data provision for consumers through adequate assessment of food value in the pet food industry. <italic>In vitro</italic> digestion models have attracted attention because they are highly reproducible and can replace animal models. Therefore, we aimed to develop an <italic>in vitro</italic> system to predict the apparent total tract digestibility (ATTD) of CP in adult dogs using an <italic>in vitro</italic> digestion method and a statistical analysis. The experimental diets used chicken meat powder as the protein source, with CP levels of 20% (22.01%, analyzed CP value as dry-based), 30% (31.35%, analyzed CP value as dry-based), and 40% (41.34%, analyzed CP value as dry-based). To simulate <italic>in vivo </italic>digestive processes a static <italic>in vitro</italic> digestion was performed in two steps; stomach and small intestine. To analyze ATTD the total fecal samples were collected in eight neutered beagle dogs during the experimental period. CP digestibility was calculated by measuring CP levels in dog food, <italic>in vitro</italic> undigested fraction, and dog feces. In result, CP digestibility at both <italic>in vivo</italic> and <italic>in vitro</italic> was increased with increasing dietary CP levels. To estimate <italic>in vivo</italic> digestibility the co-relation of <italic>in vivo</italic> ATTD and <italic>in vitro</italic> digestibility was investigated statistically and a regression equation was developed to predict the CP ATTD (% = 2.5405 × <italic>in vitro</italic> CP digestibility (%) + 151.8). The regression equation was evaluated its feasibility by using a commercial diet. The predicted CP digestibility which was calculated by the regression equation showed high similarity (100.16%) with that of <italic>in vivo</italic> in dogs. With that, it would be a feasible non-animal method to predict <italic>in vivo</italic> CP digestibility by using <italic>in vitro</italic> digestion method and the proposed linear regression equation in adult dogs.