Voluntary feed intake and nutrient composition in chickens

The phenomenon of feed intake response trends to differing feed energy and protein levels is reviewed. Increased interest in this concept is attributed to problems associated with maintaining adequate feed intake in many farms. This becomes an important factor limiting productivity. Though the spectrum of factors that affect voluntary feed intake in poultry is very broad, it is important to highlight the influence of dietary factors, particularly, energy and protein densities on voluntary feed intake responses in chickens. In formulating poultry diets, the nutrient requirements of broiler chickens have frequently been expressed per unit of dietary metabolizable energy. This practice is based on the theory that birds will adjust their feed intake according to their metabolisable energy requirements. However, based on a re-evaluation of numerous research data the application of specific nutrient-to-metabolisable energy ratios in broiler chickens becomes questionable. Many studies have shown that feed intake responses in chickens offered diets differing in feed energy and protein levels are influenced by the level of the first limiting nutrient in the feed rather than the feed energy level per se. This observation on limitations in feed intake, in effect, challenges the strongly held theory that all chickens will consume diets to meet their energy requirements and thereby achieve their genetic potential for growth. Thus, because of the important implications of these differences, both the energy and protein levels of the diet should be taken into account when formulating diets aimed at achieving optimal feed intake in growing chickens.