Nonlinear mixed models to study metabolizable energy utilization in broiler breeder hens

Abstract

This study developed mathematical models to overcome limitations of linear models of energy partitioning in hens. The fit of 1 linear and 2 nonlinear models of ME intake (MEI) were compared, using empirical data of 288 caged broiler breeder hens from 20 to 60 wk of age. Pullets were individually caged at 16 wk and assigned to 1 of 4 feed allocation groups. Three groups had feed allocated on a group basis with divergent target BW: standard (STD), HIGH (STD x 1.1), and LOW (STD x 0.9). The fourth group had individual-based feed allocation (IND) and followed the STD BW target. The linear model expressed MEI as a function of BW(0.75), ADG, egg mass (EM), and temperature. Nonlinear mixed models employed a normally distributed term associated with hen metabolic BW, and exponential terms of ADG and EM, or Cobb-Douglas form interactions between terms. Fit was evaluated with the Bayesian information criterion and systematic bias was analyzed through linear regressions of observed versus expected values. The linear model estimated energy partitioned to maintenance and retention in the range of reported values in the literature. However, this model had the poorest fit (R(2) = 0.64) and exhibited a slope bias of 0.91 (i.e., MEI was overestimated at low values and underestimated at high values). The first nonlinear mixed model indicated that MEI partitioned to ADG was a factor of ADG(1.15), whereas the ME partitioned to EM was a factor of EM(1.12). This model had improved fit (R(2) = 0.71) relative to the linear model. The second nonlinear mixed model indicated that the energy requirement for ADG increased by 0.60% and the EM energy requirement decreased by 2.07% for each 1% increment in BW. This model further improved fit (R(2) = 0.75). Nonlinear mixed models reduced estimation bias by accounting for individual variation in maintenance energy expenditure. These nonlinear mixed models may be used to analyze energy partitioning in animals, to develop prediction equations of MEI, to evaluate individual efficiency for maintenance, and to assess diets regarding the slope of bias in coefficients of maintenance energy requirements.

Effects of maternal energy efficiency on broiler chicken growth, feed conversion, residual feed intake, and residual maintenance metabolizable energy requirements

“…Broilers were retrospectively assigned to 1 of 2 RME mmat categories. not different from 1 (P > 0.05), the current model did not include these features used in the broiler breeders model (Romero et al, 2009d). Additionally, instead of assuming a fixed metabolic BW exponent such as 0.75, this model estimated it as 0.60, which avoided systematic bias in ME intake estimation.…”

“…The model used for broiler RFI and RME m estimation (Table 3) was consistent with the broiler breeder model proposed by Romero et al (2009d), with regard to the assumption of variability in maintenance requirements among birds. Maintenance estimates were also assumed to be dependent on the relative feed intake of birds (Table 4).…”

“…The RFI was defined as the difference between observed and predicted ME intake, with lower RFI values indicating greater energy efficiency. Hen RFI was calculated from 20 to 56 wk using individual weekly metabolic BW (kg 0.75 ), environmental temperature (T; °C), ADG (g/d), and egg mass (EM; g/d) data to explain daily ME intake (MEI d ; kcal/d) with a linear model as reported by Romero et al (2009d). The RFI m was the observed minus the predicted ME intake from equation [1]…”

“…Based on models of energy partitioning developed by Romero et al (2009d), an energy balance function was selected to fit the broiler data using the Nlmixed Procedure of SAS (SAS Institute Inc., Cary, NC), with the specification of equations [4] and [5]:…”

Effects of environmental temperature and dietary energy on energy partitioning coefficients of female broiler breeders1

“…In the current experiment, optimal biological efficiency was predicted at 24.3°C in feedrestricted broiler breeders fed the HE diet. in body composition, egg composition, or the composition of BW gain (Romero et al, 2009b).…”