Protein quality in blood meal: I. The rat as a model animal for determining apparent ileal amino acid digestibility in the growing pig

The laboratory rat was evaluated as a model animal for the growing pig for determining apparent amino acid digestibility in blood meal. Two test diets were formulated for rats and two for pigs. The sole source of dietary protein was blood meal and each pair of diets contained a low- and high-quality blood meal. Chromic oxide was included in the diets as an indigestible marker. On day 14 of the study ileal digesta were collected after slaughter of the rats and pigs, three and seven hours from the start of feeding, respectively. The apparent ileal digestibilities of amino acids were similar between the rats and pigs although a significant ( p < 0.05) inter-species difference was found for serine and the rat had a markedly lower apparent digestibility of methionine (33.7 vs. 42.6) in the low-quality meal, though the difference was not statistically significant. Overall mean apparent ileal amino acid digestibilities for the rat and pig were 44.7% and 46.8%, and 84.1% and 86.7%, respectively, for the two blood meals. Regression analysis in which rat digestibility was fitted as a covariate indicated a significant ( p < 0.006) relationship between rat and pig amino acid digestibility in blood meals and pig amino acid digestibility coefficients can be accurately predicted based on rat digestibility data. The rat thus appears to be a suitable model animal for the pig for determining apparent ileal nitrogen and amino acid digestibility in blood meal.