Response surface approach to studying the protein and energy requirements of laying hens

Two experiments were conducted with hens from 20 to 44 wk of age housed in cages. There were 384 hens in Experiment 1 and 360 hens in Experiment 2. The hens were fed various levels of protein and energy in a factorial arrangement in Experiment 1 and in a central composite rotatable design in Experiment 2. The diets contained primarily ground corn, soybean meal, wheat middlings, and poultry oil. Production responses to dietary protein and MEn were found to be nonlinear in nature and thus conformed to the law of diminishing marginal returns. Protein by MEn interactions, when significantly different from zero, were small in magnitude. Variability in hen performance (as measured by hen-day egg production, feed consumption, egg weight, and body weight gain) could be described better by using dietary protein and energy levels than the energy to protein ratio.