Interaction of Dietary Metabolizable Energy and Protein in Laying Hen Diets

Single Comb White Leghorn pullets, housed in colony cages, were employed in this study to investigate the effects of dietary protein and metabolizable energy (ME) levels on performance. The treatments consisted of dietary ME levels of 2.42, 2.64, 2.86, and 3.08 kcal/g of diet with each fed in diets containing 14, 16 and 18% protein to provide a 4 × 3 factorial design. At the 14% protein level, increasing the dietary energy produced a progressive decrease in egg production rate, but an improvement in feed conversion (kg/dozen eggs). The protein intake levels for birds fed these diets varied from 18.3 to 15.0 g/bird/day as the dietary energy was increased. Birds fed 16% protein showed increased egg production as the ME of the diet was increased. Regression analyses suggested a 2.25% increase in egg production for each .22 kcal ME increase/g feed. Protein intakes varied from 19.4 to 17.0 g/bird/day in this series. The 18% protein diet resulted in protein intakes of 19.2 to 22.1 g/bird/day and less response in egg production than was obtained at 16% protein with increased levels of ME from added fat. The calculated protein intake requirement during the first 12 weeks of the study (December to March) was 17.92 g/bird/day to support 84.8% egg production. During the second 12 weeks (March to May) the requirement was estimated at 16.5 g protein/bird/day at 77.2% egg production; while during the last 12 weeks (May to July) a requirement of 13.0 g/bird/day was determined at a 61.7% egg production rate. Calculations of grams of protein needed per egg during each of the three periods yielded values of 21.1 to 21.4 g. Increasing the dietary ME with added fat produced an average decrease of 5.1 to 8.3 g feed/bird/day for each increase of .22 kcal ME/g feed. These dietary changes also resulted in increased ME intakes amounting to 3.4, 10.8, and 9.9 kcal/bird/day for the three protein levels.