Effect of early protein restriction on growth and subsequent performance of egg-type chickens

Abstract

Fifteen crosses of day-old Shaver Single Comb White Leghorn egg-type chicks were used to study the effect of early protein restriction on growth and subsequent performance during lay. Four dietary protein regimes (starter-grower/developer-layer protein levels) 17-16-16, 17-16-18, 20-16-16 and 20-16-18 percent were fed during the study. Each cross consisted of 225 chicks which were separated into four groups, two of which were randomly assigned to receive either a 20% protein or 17% protein starter diet. The two starter diets were formulated to be isocaloric, containing 2924 kcal ME/kg of feed, and were fed to the chicks for the first eight weeks of growth. Feed and water were fed ad libitum during the test period. At both six and eight weeks of age, protein restriction resulted in lighter birds, shorter shank (tarsometatarsus) bones and a reduction in feed consumption per bird. Unlike the slow growing birds, the fast growing birds that were protein restricted showed evidence of an early rebound in body weight by compensatory growth after six weeks of protein restriction. From the beginning of the ninth to the end of the eighteenth week all birds were fed the same grower/developer basal diet containing 16% protein and 3056 kcal ME/kg of feed. Generally, the protein restricted birds continued to maintain smaller body frames and body weights, shorter shanks and reduced feed consumption per bird compared with the protein un-restricted birds at both 12 and 18 weeks of age. The slow growing crosses that were protein restricted made a phenomenal rebound in body weight between 12-18 weeks of age, demonstrating a "delayed compensatory growth" compared with the fast growing crosses. Feeding a high protein (18%) layer diet as compared to a low protein (16%) diet during lay to the crosses that were protein restricted for the first eight weeks of growth significantly increased adult body weight, egg size and shell weight per egg, but did not significantly improve egg production, livability, yolk size or albumen per egg, shell thickness or any egg quality factor investigated. A 17-16-16 protein feeding regime is recommended for the Single Comb White Leghorn egg-type birds. Cross genotypes significantly influenced all traits evaluated.