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.

Keywords: daylength; efficiency; maintenance requirements; residual heat production.

Figure 1

Residual feed intake (RFI) estimated from 2 to 54 wk of age for individual birds with a nonlinear model (I), 2 nonlinear mixed models with 1 random term linked with metabolic BW (associated with each individual [II] or age [III]), and a nonlinear mixed model with 2 nested random term (IV) to describe ME partitioning to maintenance, gain, and egg production. Abbreviation: ME, metabolizable energy.

Figure 2

Energy requirement per gram of average daily gain as a function of BW estimated by 4 models explaining average daily ME intake as a function of metabolic BW, gain, and egg mass. Abbreviation: ME, metabolizable energy.

Figure 3

Total heat production (HP) relative to average daily ME intake (MEI) for the duration of the experiment (wk 2–55) as estimated by a model describing ME partitioning to maintenance, gain, and egg production and including 2 random terms associated with individual bird and age (IV). Broiler breeders were fed to achieve the breeder-recommended BW curve (standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (high) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. Regression equation was HP = 47.74 + 0.52 × MEI + ε (P < 0.001; R² = 0.86). Abbreviation: ME, metabolizable energy.

Figure 4

Total heat production (HP) relative to average daily ME intake (MEI) during the rearing phase (week 2–week 21) as estimated by a model describing ME partitioning to maintenance, gain, and egg production and including 2 random terms associated with individual bird and age (IV). Broiler breeders were fed to achieve the breeder-recommended BW curve (Standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (High) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. Regression equation was HP = 19.83 + 0.79 × MEI + ε (P < 0.001; R² = 0.78). Abbreviation: ME, metabolizable energy.

Figure 5

Total heat production (HP) relative to average daily ME intake (MEI) during the laying phase (week 21–week 55) as estimated by a model describing ME partitioning to maintenance, gain, and egg production and including 2 random terms associated with individual bird and age (IV). Broiler breeders were fed to achieve the breeder-recommended BW curve (standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (high) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. Regression equation was HP = 55.30 + 0.44 × MEI + ε (P < 0.001; R² = 0.86). Abbreviation: ME, metabolizable energy.

Figure 6

Number of daily visits to the feeding station for broiler breeders fed to achieve the breeder-recommended BW curve (standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (high) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. The asterisks indicate ages where treatment means differed (P < 0.05); all fixed effects and interactions were significant (P < 0.001), except the interaction between age and BW treatment (P = 0.08) and the 3-way interaction between age, BW treatment, and photoschedule (P = 0.99).

Figure 7

Number of daily meals of broiler breeders fed with a precision feeding system to achieve the breeder-recommended BW curve (standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (high) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. The asterisks indicate ages where treatment means differed (P < 0.05); all fixed effects and interactions were significant (P < 0.001).

Figure 8

Meal:visit ratio of broiler breeders fed with a precision feeding system to achieve the breeder-recommended BW curve (Standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (High) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. The asterisks indicate ages where treatment means differed (P < 0.05); all fixed effects and interactions were significant (P < 0.001), except the 3-way interaction between age, BW treatment, and photoschedule (P = 0.07).

Figure 9

Meal size of broiler breeders fed with a precision feeding system to achieve the breeder-recommended BW curve (standard) or an accelerated BW curve reaching the 21 wk BW at 18 wk (high) and reared to week 21 on an 8L:16D, 10L:14D, or 12L:12D photoschedule. The asterisks indicate ages where treatment means differed (P < 0.05); all fixed effects and interactions were significant (P < 0.001), except the 3-way interaction between age, BW treatment, and photoschedule (P = 1.00).