Comparison of mathematical and comparative slaughter methodologies for determination of heat production and energy retention in broilers

Abstract

Understanding factors affecting ME availability for productive processes is an important step in optimal feed formulation. This study compared a modelling methodology with the comparative slaughter technique (CST) to estimate energy partitioning to heat production and energy retention (RE) and to investigate differences in heat dissipation. At hatch, 50 broilers were randomly allocated in one of 4 pens equipped with a precision feeding station. From day 14 to day 45, they were either fed with a low-ME (3,111 kcal/kg ME) or a high-ME (3,383 kcal/kg ME) diet. At day 19, birds were assigned to pair-feeding in groups of 6 with lead birds eating ad libitum (100%) and follow birds eating at either 50, 60, 70, 80, or 90% of the paired lead's cumulative feed intake. Heat production and RE were estimated by CST and with a nonlinear mixed model explaining daily ME intake (MEI) as a function of metabolic BW and average daily gain (ADG). The energy partitioning model predicted MEI = (145.10 + u) BW^0.83 + 1.09 × BW^-0.18 × ADG^1.19 + ε. The model underestimated heat production by 13.4% and overestimated RE by 22.8% compared with the CST. The model was not able to distinguish between net energy for gain values of the diets (1,448 ± 18.5 kcal/kg vs. 1,493 ± 18.0 kcal/kg for the low-ME and high-ME diet, respectively), whereas the CST found a 148 kcal/kg difference between the low-ME and high-ME diets (1,101 ± 22.5 kcal/kg vs. 1,249 ± 22.0 kcal/kg, respectively). The estimates of the net energy for gain values of the 2 diets decreased with increasing feed restriction. The heat increment of feeding did not differ between birds fed with the low- or high-ME diet (26% of MEI). Additional measurements on heat dissipation, physical activity, and immune status indicated that the energetic content of the diet and feed restriction affect some parameters (shank temperature, feeding station visits) but not others (leukocyte counts, heterophil to lymphocyte ratio, and immune cell function).

Keywords: energetic modeling; maintenance; net energy.

Figure 1

Retained energy (RE) estimated by a nonlinear equation explaining ME intake as a function of metabolic BW and gain (model) compared with the RE estimated by the comparative slaughter technique (CST) of broilers fed with either a low-ME (3,111 kcal/kg) or high-ME (3,383 kcal/kg) diet from day 14 to day 45, where the model overestimated RE. The solid gray line indicates where the model would have estimated the same value as the CST.

Figure 2

Total heat production (HP) estimated by a nonlinear equation explaining ME intake as a function of metabolic BW and gain (model) versus that calculated through the comparative slaughter technique (CST) of broilers fed with either fed a low-ME (3,111 kcal/kg) or high-ME (3,383 kcal/kg) diet from day 14 to day 45, where the model underestimated HP. The solid gray line indicates where the model would have estimated the same value as the CST.

Figure 3

ME requirement per gram of average daily gain (ADG), as a function of body weight (BW) and ADG, as predicted by a nonlinear model explaining ME intake as a function of metabolic BW and gain of broilers from day 14 to day 45. The estimated equation was MEI_d = (145.10 + u) BW^0.83 + 1.09 × BW^−0.18 × ADG^1.19 and u ∼ N(0, V_u), MEI_d ∼ N(μ,V), where MEI_d = daily ME intake (kcal/D), BW = body weight (kg), and ADG = average daily gain (g/D). The error term u was associated with each bird. The second part of the equation (1.09 × BW^−0.18 × ADG^1.19) represented retained energy (gain) per day.

Figure 4

Linear regression of heat production (HP) and average daily ME intake (ME intake) per unit of metabolic BW (kg^0.83) as estimated by the comparative slaughter technique of broilers fed with either a low-ME (3,111 kcal/kg) or high-ME (3,383 kcal/kg) diet from day 14 to day 45. Linear regression equations were: HP = 95.64 kcal + 0.26 × ME intake for the Low ME diet and HP = 95.44 kcal + 0.26 × ME intake for the High ME diet.