Broiler growth models dynamically interfacing metabolic efficiency with the production environment

Abstract

Scope and Method of Study: Experiments were conducted with broilers (Cobbs 500) to: 1) validate dual energy x-ray absorptiometry (DEXA) as a method for quantifying body composition; 2) establish a methodology for predicting effective caloric value (ECV) and quantify the ECV attributable to pellet quality (PQ); and 3) Test and or refine methodologies used to estimate energetic efficiency of energy consumed above maintenance for protein (kp) and lipid (kf) tissue accretion.

Findings and Conclusions: DEXA measurements applied to developed regression equations successfully inter-related DEXA measurements with body compositions obtained by proximate analysis. Thus, DEXA was validated as a method for quantifying body composition in poultry. Regression equations developed provide a method for estimating ECV of nonnutritive factors that impact body weight and or feed conversion ratio. Use of this methodology suggests that pelleting contributes 187 kcal ECV to the diet at 100% PQ and that the ECV declines curvilinearly as PQ falls. Further, application reveals potential for creation of formulation "dead zones" whereby dietary changes to enhance caloric density may be offset due to reduced ECV. Regression analysis separating retained energy into energy retained as protein and lipid tissue overestimate values for kp and kf. These overestimations were attributed to the colinearity between protein and lipid tissue accretion. To circumvent this, a novel methodology was developed as follows: first a matrix of biologically possible kp and kf values is created, followed by its application to predict ME intake above maintenance. This proposed methodology for calculating kp and kf appears to provide more accurate estimates.