The fasting heat production of broilers is a function of their body composition

The fasting heat production (FHP; net energy expenditure under maintenance) is a key value to determine the net energy value of the feed and is calculated from measurements in respiratory chambers or predicted as a function of the metabolic BW (MBW). This study aimed to determine the influence of body composition on the FHP of broilers through a modeling approach. Six experiments (Exp 1–6) were conducted to develop (Exp 1–4) and externally validate (Exp 5 and 6) predictive models. In Exp 1–4, broilers of a single genetic line in floor pens were subjected to three dietary treatments to induce differences in body composition. The FHP (calorimetry chambers) and the body protein-to-fat ratio (PFR; Dual-Energy X-ray Absorptiometry) were recorded at nine time points between 7 and 55 days. Linear models were adjusted (considering the pen as the experimental unit), starting with a model containing the MBW as the sole predictor. Further modifications were tested by including the PFR and the age of the birds. A random split with a refitting approach was applied. Four models were internally validated and refitted to the whole data. They considered the FHP a function of the MBW (or BW) and the PFR, including or not the age of the birds, and showed high precision (R2 > 0.98) and accuracy (error 0.92) and accuracy (model prediction error