A comparison of methods for rehabilitating aging hens

Abstract

Three of five groups of White Leghorn x Australorp hens aged 73 weeks, housed in cages, were fed a laying diet containing zinc (23.7 g/kg), or iodine (4.1 g/kg), or calcium (1.0 g/kg). The fourth group of hens was given only whole-grain barley while a fifth group given a normal laying diet served as the control. All groups were fed their respective diets until rate of lay dropped to 0% or less than 2%, and they were then given a normal laying diet until 97 weeks of age. Water was available at all times and 15.5 h of constant light was provided daily to all treatments throughout the experiment. Hens given the zinc and the whole-grain barley diets ceased egg production within 1 week and remained out of production for about 10 days. The hens in both of these treatments reached peak egg production (67%, on a hen day basis) 8 weeks after the initiation of treatments, after which they continued to lay at a higher rate than those given iodine, calcium and control treatments. Hens given the diets with either iodine or calcium reached their lowest rate of lay (1.6%) after 15 and 7 days of feeding the two diets respectively. They resumed laying immediately after the resumption of feeding the normal laying diet and reached peak egg production (59%) at 8 and 12 weeks after feeding the iodine and calcium diets respectively. The treated hens laid eggs with higher Haugh units and specific gravity values than those eggs of the controls. The lowest rate of decline in both those traits, from the pre-treatment values, was in the zinc and barley treatments. These treatments also had the lowest percentage of cracked eggs. There was no significant difference among treatments in mean rate of lay, egg weight, or rate of mortality from 73 to 97 weeks of age. The present results suggest that feeding wholegrain barley can be used successfully to extend the productive life of laying hens beyond the first year of egg production if such an extension is desirable in a given economic situation. It is a simpler technique than the conventional method of induced moulting and the method of feeding a high level of zinc.