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Mathematical models have become increasingly popular to help understand energy partitioning. These energy partitioning models have focused previously on either the growing period or the laying period Although energy partitioning estimates for each period separately are important, models could be improved including both phases such that the effect of age on energy partitioning and the efficiency of growth and egg production over their life-time can be studied. The aim of this study was to compare 4 different models partitioning ME intake to BW, average daily gain (ADG), and egg mass (EM) over the lifetime of group housed broiler breeders fed with the Precision Feeding system (PF) system. Model fit and bias were compared. The best fitting model was used to estimate residual feed intake (RFI) and residual heat production (RHP).
The experiment was conducted as randomized block design of a 2 × 3 factorial arrangement of treatments with pullets (Ross 708, n=180) reared either on a breeder-recommended target BW curve or an accelerated target BW curve reaching the 21 wk BW at 18 wk (high) and maintained under 8L:16D, 10L:14D, or 12L:12D photoschedules during rearing. The PF system recorded individual BW and individual feed intake for every feeding bout. Pullets were fed using the PF. For the first 3 wk, birds received a standard wheat based starter diet (2,900 AME, 19% CP, 1.1% Ca); from week 4 to week 23, pullets received a wheat and barley-based grower diet (2,589 AME, 14.2% CP, and 0.9% Ca); from week 23 to week 34, hens received a wheat-based peak layer diet (2,689 AME, 15.0% CP, and 3.3% Ca); and from week 35 to week 55, hens received a wheat-based postpeak layer diet (2,682 AME, 14.6% CP, and 3.3% Ca). Birds were weighed at least daily, either manually or by the PF system before feeding. Cloacae of all hens were palpated daily to detect hard-shelled eggs in the shell gland to measure age at first egg and individual egg production from 20 wk to 36 wk. Four models were evaluated: 1 nonlinear model, 2 nonlinear mixed models with 1 random term, and 1 nested nonlinear mixed model with 2 random terms.
Treatments significantly differed in age at first egg and egg production. Of the Standard BW hens on the 8L:16D, 10L:14D, and 12L:12D photoschedules, 3.3, 18.1, and 37.6%, respectively, never commenced egg production throughout the experiment. All models converged. A variation on model IV was initially attempted, where the random term associated with the individual bird was nested within the random term of age. However, this model would not converge or was unstable, depending on the starting parameters. Model I and III estimated slightly higher values, potentially because these models did not appropriately account for sources of variation. Individuals varied substantially in egg production and unaccounted individual variation in MEm requirements related to an increased feed intake for egg production was likely accounted for in the EM coefficient. Model III showed very different values for ME requirements for gain compared with the literature and compared with the other models.
This is the first time an energy partitioning model was developed using individual data from both the rearing and the laying phase of broiler breeders housed in a free-run setting. Including random terms for both individual and age-related variation in MEm requirements resulted in a biologically sound estimation of ME partitioning to maintenance, gain, and egg production for both the rearing and the laying phase and reduced residuals substantially. Understanding energy partitioning estimates for each over the bird’s life-time can benefit nutritionist and breeding companies as understanding of energy partitioning would provide tools to minimize energy loss to heat.