Changes in dietary protein level during the pullet year

Abstract

A “High” protein diet (14 per cent crude protein, 2490 k cal. ME/kg.) and a “Low” protein diet (10.5 per cent protein, 2420 k cal. ME/kg.) were fed to two types of laying pullet. One type was a small commercial hybrid weighing about 1.6 kg. and the other was a large first cross weighing about 2.4 kg. at 20 weeks. After 12 weeks and 24 weeks of lay, groups were transferred from the High to the Low protein diet and vice versa. In the heavy strain birds the High and Low protein diets both supported good egg production throughout the trial and changing from High to Low protein had no effect on rate of lay. The opposite change from Low to High, made after 12 weeks of lay, stimulated an increase in rate of lay above the level of birds which had received the High protein diet throughout. In the small hybrid pullets the low protein diet did not support a normal rate of lay. Attempts to reduce dietary protein by switching from High to Low after 12 or 24 weeks caused a fall in rate of lay. Groups transferred from Low to High increased their rate of lay to a level comparable with controls kept on High protein throughout. Egg weight and body weight were affected by dietary protein level in both strains. Changes in the diet caused corresponding changes in both egg weight and body weight. It is concluded that there is little scope for reducing the level of protein in the diet during the laying year. If a diet is inadequate in the early stages of production it is likely to remain inadequate for any later stage. On the other hand, some unexpected benefit was obtained in one strain by increasing the dietary protein beyond the level which was adequate for maximum egg production in the first 3 months of lay.