Prediction of energetic value of wheat and triticale in broiler chicks: A chick bioassay and an in vitro digestibility technique

Abstract

Variation in apparent metabolizable energy (AME) of diets is a concern in poultry feeding. Thus, predicting variations in AME content of cereal grains is important, because this will allow a more accurate diet formulation. Eight samples, six wheat and two triticale, were collected from western Canada and a modified chick bioassay was used to determine their nitrogen-corrected AME (AMEn) content for broiler chicks. A total of 768 one-d-old male broiler chicks were randomly assigned to 8 dietary treatments (8 cages per treatment and 12 chicks per cage). Birds were fed a starter diet from 0 to 7d of age and experimental diets were fed from 7 to 13d of age. The experimental diets were composed of 80% of test sample and the remaining 20% was a combination of other ingredients held constant across diets. Digestibility of nutrients and energy differed significantly among birds fed the experimental diets. The AMEn values of the test samples determined in the bioassay ranged from 12.7MJ/kg of DM for Canada Western Soft White Spring sample to 14.6MJ/kg of DM for Canada Western Amber Durum sample. Energetic values of the 8 test samples were also evaluated using a two-step in vitro digestibility technique simulating digestive processes in broiler chicks. In vitro AME value of the test samples were calculated and related to in vivo AMEn by regression analysis. The equation for prediction of in vivo AMEn based on in vitro AME was: In vivo AMEn (MJ/kg of DM)=5.4108+0.7016×in vitro AME (R2=0.81, standard error of prediction (SEP)=0.22MJ/kg, P=0.002). Inclusion of other energy-related characteristics of test samples (e.g., starch, ether extract, and crude protein) into the regression equation increased the R2 and decreased the SEP. Specifically, inclusion of neutral detergent fiber, ether extract, starch, and crude protein of samples together with the in vitro AME resulted in the strongest prediction equation for in vivo AMEn (R2=0.99, SEP=0.05MJ/kg, P=0.014). The predicted in vivo AMEn of test samples ranged from 12.7 to 14.5MJ/kg of DM. In conclusion, this in vitro digestibility technique accurately predicted in vivo AMEn of wheat and triticale samples for broiler chickens and can serve as a reference analysis to develop calibration equations for rapid feed quality evaluation methods such as near infrared reflectance spectroscopy (NIRS).