Duck feed guidelines are often copied fromchicken nutrition books. Although research on duck nutrition is scarce, especially publicly available work,feeding ducks as ducks is necessary for large-scale operations to reap the full benefits from rearing this highly profitable species of poultry.Indeed, ducks reared for meat are not only of highest value to Asian markets, but in Europe and the United States there is a growing trend to produce duck meat for export and, most importantly, for local consumption. Thus, as duck rearing becomes a highly sophisticated business, nutrition should match pace. To this end, dietary protein is perhaps the first cost-determining factor, worldwide.Crude protein levelsIn extensive rearing systems, and in areas where protein-rich ingredients are too expensive, most ducks are reared on a single diet, from birth to market age, with about 14-15 percent crude protein. Although, this is sufficient enough for ducks to grow, it slows them down considerably. For instance, in a commercial study, ducks fed a diet containing 16 percent crude protein (birth to market age) required about 3 days longer to achieve equal body weight compared to ducks fed a diet containing 21 percent crude protein during the first two weeks post-hatch, and 16 percent thereafter. This is a prime example where excellent early nutrition appears to pay off long term. One further interesting observation is coming from free-choice feeding experiments: It has been observed that unselected genotypes require about 18 percent crude protein for growth, whereas selected genotypes require at least 21 percent crude protein to exhibit their full potential for growth.In practical terms, assuming a two-phase feeding program (0-14 and 14-42 days of age, with a final live weight of 3.2 kg) for commercial pekin ducks, with an average metabolizable energy concentration equal to 12-13 Mj/kg, we can propose the following crude protein levels:These are, of course, very generic guidelines. Feed conversion efficiency will vary according to actual energy levels, and, consequently, cost per kg growth will depend on cost per Mj metabolizable energy. In many cases, the least expensive feed might not be the most profitable, whereas in other cases, a less expensive feed might be the best solution. Here it should be emphasized that ducks can tolerate quite wider flactuations in dietary energy concentration compared to chicken. Thus, they can use higher levels of fibrous ingredients, which under certain conditions can be quite attractively priced compared to more conventional feedstuffs like maize and soya beans.As ducks are favored as much for their fat as for their meat, an optimum balance of fat versus lean concentration in carcass is required to ensure consumer acceptance. The energy to protein ratio greatly affects this balance, in all genotypes, especially during the finishing phase. As the energy to protein ratio widens (more energy for the same protein or less protein), carcass fat increases in a linear way. In fact, in certain commercial rearing settings there is in use a set of equations that determines the actual dietary energy and protein levels required to achieve desired carcass composition. As it can be imagined, this exercise is quite unique for each genotype and management system, but it can serve as an example of how sophisticated duck nutrition can be.