Effect of Intake and Source of Protein on Laying Performance of Seven Strains under Single and Double Cage Housing

An experiment was conducted to compare the laying house performance of 7 strains of White Leghorns, housed at two different densities (1 and 2 birds per 8″ × 16″ cage) when fed 7 diets differing in protein and energy levels. The test started with 2366 pullets, and lasted for 336 days. Performance criteria were egg production, egg weight, body weight, feed consumption, mortality and egg quality. There were large real differences among strains in all performance traits. Compared to birds housed 1 per cage, those housed 2 in a cage laid 9% fewer eggs per hen housed, suffered 1.5 times as much mortality, gained 130 g. less weight from 20 to 64 weeks of age, consumed 3% more feed and required 8% more feed per unit weight of eggs produced, but eggs did not differ in size, specific gravity, albumin quality, shell shape or blood spots. Shells were slightly whiter at 225 days of age and rougher at 450 days of age in the 2 bird cages. Protein intake was the dietary factor most closely associated with large effects of diet on gains in body weight, egg production, egg size, feed conversion and albumin height. Average daily crude protein intake of 17 g. for the laying year appeared adequate and there were no significant strain differences in dietary effects. Strains differed markedly in voluntary nutrient intakes but not in sensitivity to the range of dietary protein and energy levels investigated. Housing birds at 2 versus 1 bird per cage reduced egg production and feed conversion significantly more at lower protein intake levels; its effects also differed appreciably among genetic stocks for feed consumption, egg weight and body weight but not for net efficiency of feed conversion.