Prediction of digestible energy content of extruded dog food by in vitro analyses.

The aim of this study was to develop a simple and reproducible in vitro method for predicting the apparent energy digestibility of dry extruded dog foods. The proposed method is based on the two-step multienzymatic incubation assay described by [Boisen, S., 1991: In Vitro Digestion for Pigs and Poultry, M. F. Fuller (ed.). CAB International, Wallingford, 135-146], with some modifications adapted to dogs' digestion characteristics. The method consisted in two consecutives incubations, first one during 2 h with pepsin (10 mg/g of food sample) in acid pH and second one during 4 h with pancreatin (100 mg/g of food sample). The undigested residue obtained was collected in a filtration unit and then dried and ashed. The in vitro percentage of organic matter disappearance (in vitro dOM) of 54 dry extruded commercial dog foods was determined and used as predictor of the in vivo apparent organic matter (in vivo dOM) and energy digestibility (in vivo dE) and digestible energy (DE) content. There was a close linear relationship between the in vivo dOM and dE [r(2) = 0.95, residual standard deviation (RSD) = 1.05 and coefficient of variation (CV) = 1.2%] and also between the in vitro and in vivo dOM (r(2) = 0.92, RSD = 1.38 and CV = 1.6%), even if the in vitro dOM overestimated on average by 4% the in vivo dOM. When the in vitro dOM was used to predict the in vivo dE, the relationship between both variables was defined by the equation: in vivo dE (%) = -2.45 + 0.98 +/- 0.04x in vitro dOM (%), (r(2) = 0.92, RSD = 1.25 and CV = 1.5%). In addition, a close relationship between the in vivo and predicted DE (estimated dE x gross energy determined calorimetrically) was found (r(2) = 0.97, RSD = 0.26 and CV = 1.4%). The accuracy of DE content prediction using the proposed in vitro method was higher than that obtained when the DE content of the same set of samples was predicted by the equation proposed by the NRC (1985) (r(2) = 0.76, CV = 4.5%) and also slightly higher than that obtained when using the equation proposed by NRC (2006) (r(2) = 0.95, CV = 2.1%).