Factorial estimation of energy requirement for egg production

Based on balance and respiration measurements with 60 White Leghorns during the laying period from 27 to 48 wk of age, a factorial method for estimating the energy requirement for egg production is proposed. The present experiment showed that the deposition of fat and energy increased during the laying period, but protein deposition slightly decreased. It has been shown that the efficiency of ME utilization for fat energy deposition is higher than for protein energy deposition in the egg. Because the proportions of protein and fat differ during the laying period, and because energy utilization is different between protein and fat, the ME requirement was calculated as the sum of ME for maintenance and the partial requirements for protein, fat, and carbohydrate deposition. For practical applications, functions for prediction of protein (OP), fat (OF), and energy (OE) in eggs during the laying period have been established according to the following model: OP, OF, or OE = a + b1 x egg (grams per day) + b2 x age (weeks). The average ME requirement [calculated with either measured or predicted chemical composition, and by applying a constant maintenance requirement of 98 kcal/kg BW.75 and partial efficiencies for energy retention in protein (Kop = .50), fat (Kof = .79), and carbohydrates (Koc = .79)] increased from .26 Mcal at 27 wk of age to .29 Mcal at 48 wk, corresponding to 5.93 and 6.07 Mcal/kg egg.