Search

The aim of this study was to check the accuracy of laboratory methods to predict the apparent protein digestibility (CPd, %) and digestible protein content (DP, g/kgDM) of dog foods, avoiding the use of experimental animals in digestion trials. Twenty-eight commercial dry extruded dog foods were tested by three different methodologies: an adaptation of the in vitro incubation method described by Hervera et al. (J Anim Physiol Anim Nutr 2007, 91: 205) for estimation of digestible energy of commercial dog foods, a modification of the pH drop methodology proposed by Hsu et al. (J Food Sci 1977, 42: 1269) for protein evaluation of human foods and the Near Infra Red Spectroscopy (NIRS) technology. All the methods assessed revealed very good, similar accuracy in the prediction of DP content either using the in vitro method (r = 0.99; RSD = 6.76; CV = 2.31%), the pH drop method (r = 0.99; RSD = 6.94; CV = 3.02%) or the NIRS (R2 = 0.96; SECV = 10.50) method, although the in vitro digestion method showed the highest accuracy approach of in vivo crude protein apparent digestibility: CPd in vitro (r = 0.81; RSD = 2.01; CV = 2.41%); CPd pH-drop (r = 0.78; RSD = 2.48; CV = 2.98%) and NIRS (r(2)cv = 0.53; SECV = 2.37).

The proposal of National Research Council (NRC), based on the use of modified Atwater factors, is nowadays the widely used method to estimate digestible energy (DE) content of pet foods. Recently, alternative methods have been suggested for predicting energy content of commercial canine dry food. Factorial equations including food fibre content as estimator, in vitro digestions methods or near-infrared spectroscopy (NIRS) techniques have been considered as good approaches to predict the energy content of dog foods. The aim of this study was to compare the accuracy of some of those estimation methods. Seventeen samples of commercial extruded dog food were used to validate and compare some estimation methods of energy digestibility (Ed, %) and DE value [MJ/kg dry matter (DM)]. The apparent Ed and DE of each food were previously determined by in vivo trials. In vivo Ed and DE of foods ranged from 79.30% to 91.05% and from 16.25 to 21.82 MJ/kg DM, respectively, and their crude fibre (CF) content ranged from 0.72% to 3.28% (in DM base). The % Ed of each sample was estimated by the factorial equation (% Ed = 91.2 - 1.43 x CF %) and by the in vitro digestion method [% Ed(in vitro) = -2.45 + 0.98 organic matter (OM) disappearance(in vitro)%]. The set of samples also was analysed by NIRS, using a calibration equation developed from a set of 69 samples of commercial extruded dog food (0.76 and 0.89 cross-validation r(2) and 2.33 and 0.61 cross-validation SE for Ed and DE respectively). The in vitro method gave better estimations of Ed in vivo than NIRS and factorial methods, although all the methods assessed showed a very good and similar accuracy in the prediction of DE value. These three methods showed a slight better accuracy than that previously proposed by the NRC. To consider constant digestibility values of nutrient content of food can result in bias and error in the estimated energy values. The alternative prediction methods used in this study take into account differences of ingredient composition and availability of nutrients of different extruded dog foods thus could be better systems of valuating energy content in a wider range of different kind of foods than in use method.

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%).

Near-infrared spectroscopy (NIRS) is used in the pet food industry for rapid assessment of several macronutrients and GE content, but there is little published data on its usefulness for evaluating GE and GE digestibility (GED) of commercial pet food. Using NIRS spectra of 71 commercial extruded dog foods and reference values determined with calorimetry and in vivo feeding trials, chemometric models were developed for GE, GED, and DE prediction. The SE and R2 of cross-validation were 0.30 MJ/kg DM and 0.93 for GE, 2.10% and 0.82 for GED, and 0.53 MJ/kg DM and 0.92 for DE. The results indicated that NIRS provides GE, GED, and DE estimation values for dog food with an accuracy similar to that of the 2006 NRC proposed equations for use in pet food. Near-infrared spectroscopy is a fast and accurate method for predicting energy content in commercial extruded dog food, and is a useful and reliable tool to be used by the pet food industry when a wide enough calibration set is available. [ABSTRACT FROM AUTHOR]