Modeling life-time energy partitioning in broiler breeders with differing body weight and rearing photoperiods

Abstract

Understanding energy partitioning in broiler breeders is needed to provide efficiency indicators for breeding purposes. This study compared 4 nonlinear models partitioning metabolizable energy ( ME ) intake to BW, average daily gain ( ADG ), and egg mass ( EM ) and described the effect of BW and rearing photoperiod on energy partitioning. Ross 708 broiler breeders (n = 180) were kept in 6 pens, controlling individual BW of free run birds with precision feeding stations. Half of the birds in each chamber were assigned to the breeder-recommended target BW curve (Standard) or to an accelerated target BW curve reaching the 21-week BW at week 18 (High). Pairs of chambers were randomly assigned to 8L:16D, 10L:14D, or 12L:12D rearing photoschedules and photostimulated with 16L:8D at week 21. Model [I] was: MEI d = a × BW b + c × ADG × BW d + e × EM + ε, where MEI d = daily ME intake (kcal/day); BW in kg; ADG in g/day; EM in g/day. Models [II–IV] were nonlinear mixed versions of model [I] and included individual [II], age-related [III], or both individual and age-related [IV] random terms to explain these sources of variation in maintenance requirement (a). Differences were reported as significant at P ≤ 0.05. The mean square error was 2,111, 1,532, 1,668, and 46 for models [I–IV] respectively, inferring extra random variation was explained by incorporating 1 or 2 random terms. Estimated ME partitioned to maintenance [IV] was 130.6 ± 1.15 kcal/kg 0.58 , and the ME requirement for ADG and EM were 0.63 ± 0.03 kcal/g/kg 0.54 and 2.42 ± 0.04 kcal/g, respectively. During the laying period, maintenance estimates were 124.2 and 137.4 kcal/kg 0.58 for standard and high BW treatment, and 130.7, 132.2, and 129.5 kcal/kg 0.58 for the 8L:16D, 10L:14D, or 12L:12D treatments, respectively. Although hens on the standard BW treatment with a 12L:12D rearing photoschedule were most energetically conservative, their reproductive performance was the poorest. Model IV provided a new biologically sound method for estimation of life-time energy partitioning in broiler breeders including an age-related random term.

Architecture of broiler breeder energy partitioning models

“…For instance, for a 2.00 kg bird, maintenance energy requirement (kcal/d) ranged from 147.10 to 216.33 kcal/d for the 3-wk (model [IV] – 3 wk) and daily (model [III] – daily) chunk sizes, respectively. These were similar to previously reported estimates for ME m requirement, which ranged from 147.6 to 245.2 kcal/d for a 2.00 kg broiler breeder pullet or hen ( Sakomura et al., 2003 ; Romero et al., 2011 ; Hadinia et al., 2018 ; van der Klein et al., 2020 ). An estimated ME m for a 2.00 kg broiler breeder hen in the current study was 148.1 kcal/d (119.73 × 2.00 0.49 ; based on the coefficients of model [II] – 3 wk Table 6 ), which is less than that reported by van der Klein et al.…”

“…These were similar to previously reported estimates for ME m requirement, which ranged from 147.6 to 245.2 kcal/d for a 2.00 kg broiler breeder pullet or hen ( Sakomura et al., 2003 ; Romero et al., 2011 ; Hadinia et al., 2018 ; van der Klein et al., 2020 ). An estimated ME m for a 2.00 kg broiler breeder hen in the current study was 148.1 kcal/d (119.73 × 2.00 0.49 ; based on the coefficients of model [II] – 3 wk Table 6 ), which is less than that reported by van der Klein et al. (2020) , in which weekly chunked data were used (130.64 × 2.00 0.58 = 195.1 kcal/d; based on the coefficients in the model of choice in their study).…”

“…This wide range for ME m requirement in the literature was due to animal behavior, bird age, strain, temperature, and dietary energy level. Furthermore, different housing systems (20% greater ME m requirement in floor pens than cage-raised ones; Rabello et al., 2006 ), feed intake (10% greater heat increment in ad libitum fed birds compared to that of pullets restricted to 54% of the ad libitum feed intake; Sakomura et al., 2003 ), and methodology being used to estimate ME m requirement (indirect calorimetry, Spratt et al., 1990 ; comparative slaughter method, Rabello et al., 2006 ; Reyes et al., 2012 ; mathematical modeling approach, van der Klein et al., 2020 ) could affect the estimated ME m requirement. This study revealed that chunk size of data used in modeling of ME partitioning can also affect the estimated ME m requirement.…”

“…Creating robust energy intake models is important to formulate poultry diets with optimum levels of nutrients and to make economic decisions in the poultry industry. Metabolizable energy requirement models have been developed ( Sakomura et al., 1993 , 2003 ; Sakomura, 2004 ; Rabello et al., 2006 ; Romero et al., 2009b ; Reyes et al., 2012 ; Pishnamazi et al., 2015 ; Hadinia et al., 2018 ; van der Klein et al., 2020 ) according to coefficients estimated for maintenance ME requirement per metabolic BW (kcal/W 0.75 ), daily body weight gain (kcal/g), and daily egg mass production (kcal/g). A valid estimation approach in these models should be able to estimate model coefficients with reasonable accuracy, the lowest possible bias, and the smallest variation.…”

“…We hypothesized that increasing data chunk size could account for unexplained variation in data caused by variation in health status and voluntary activity level of birds, anomalies in real-time BW data recorded by a precision feeding ( PF ) system ( You et al., 2021 ), and environmental conditions. Furthermore, the effect of including random terms associated with different model parameters (individual maintenance ME and age) on the fitting performance of the models has been investigated ( van der Klein et al., 2020 ). It is not clear how inclusion of different random terms could affect the predictive performance of ME intake partitioning models.…”