The effect of dietary protein and energy on feed intake and performance of laying hens.
This study was designed to devise a method by which the optimum combination of dietary energy and protein could be found that maximises the margin over feeding cost in an egg production enterprise. It was necessary to be able to predict feeding costs and revenue associated with the use of a wide range of feeds varying in protein and energy. To this end, two experiments were conducted using 256 Lohmann (128 White and 128 Brown) in the first, and 1296 Hy-line Brown laying birds in the second trial, that were 33 and 38 weeks old at the beginning of the two trials. Using the WinFeed 1.1 (1996) feed formulation programme, four basal (corner) feeds were formulated in both experiments, from which four protein and four energy contents (16 feeds) were produced in the first experiment, and six protein and three energy contents ( 18 feeds) were used in the second. Each feed was given to three replicates of 16 birds in the first trial, and to three replicates of 24 birds in the second. The trials each lasted ten weeks, and the data collected included food intake, change in body weight, egg weight and rate of laying. Using the results from these two experiments and from previously published research, the effects of dietary protein and energy on food intake were predicted independently, and these predictions were then used to determine the cost of feeding. Similarly, egg weight and rate of lay were predicted independently for changes in dietary protein and energy, from which the revenue could be calculated over the range of energy and protein contents. It is understood that a more integrated approach would be more accurate for this purpose, but such an approach was beyond the scope of this investigation. The use of contour plots based on regression analyses of the estimated income-minus-feeding cost on changes in dietary protein and energy enabled evaluations to be made of the effect on profitability of changes in egg price and maize price. And it was deduced that under conditions in which the maize price is high, maximum profitability is achieved with high energy and high protein content, irrespective of the price paid for eggs. When the maize price is reduced, the combination of protein and energy that yields the highest return over feed cost changes to low protein and low energy feeds. This change is defensible on the grounds that the price of high-density feeds does not change as much as that of low-density feeds when the maize price is lowered, whereas production, and hence returns, remains the same, hence the low density feeds yield higher returns under such circumstances. The method applied in this study appears to be a useful tool for decision-making by egg producers and nutritionists.