Body Weight, Flock Uniformity, Production Performance and Egg Quality over the Laying Period of Brown Egg-Laying Hens

Abstract

Genetic selection of laying hens has produced lighter body weight while maintaining maximum egg production. Heavy birds have problems during the laying period such as fatty liver and large size egg. The body weight at point of lay and flock uniformity can be used to predict the production performance during the laying period. However, there is evidence that hens which are overweight produce poor quality eggs during the laying period. The first two studies were conducted to investigate the importance of body weight at point of lay and flock uniformity on eggshell quality and production performance on commercial farms, both cage and free-range production systems. A laboratory experiment was then set up using the information derived from the on-farm studies, and extended to analyse body conformation using computed tomographic scanning. The body weight and flock uniformity in the on-farm studies varied from farm to farm. The poor performance of many of the flocks also illustrates the likely variation occurring at a commercial level; poor compliance with average growth rate patterns and low uniformity standards. Hen age had the greatest effect on most egg quality variables. In the laboratory experiment, flock uniformity prior to point of lay was designed to be above the breeder standard. Body weight at point of lay significantly affected egg production and eggshell quality. However, there was no significant effect on bone breaking strength and bone dimensions. Body weight was significantly correlated with the composition of lean, fat and bone. Heavy hens deposited more fat than lean tissue. Body weight should be maintained at the level of breeder standards. Correct body weight and high uniformity of the flock at point of lay will result in good performance over the laying period with high peak production and good persistency of production and the production of good quality eggs. Management is the key factor to regulation of body weight during rearing and at point of lay.