Cereal grains are the main source of dietary energy in poultry, and maize is the popular cereal used with protein meal, such as soybean meal, which generally determines the cost of compounded feed. Maize is high in energy, low in fibres and easily digested by most livestock species including poultry. Normal maize contributes up to one-third of the protein content of poultry diets.
Low protein levels
However, normal maize contains a high zein fraction, which is practically devoid of lysine and low in tryptophan, in addition to the low protein levels as compared to other cereals (8-10%). The poor quality of maize proteins is attributed to high concentration of prolamin storage protein fraction (50-60% of protein) which is devoid of lysine. The prolamins, being soluble in alcohol solution, are rich in proline and glutamine, but are low in basic amino acids, including lysine. The prolamin fraction is named as zein in maize. Thus, use of maize necessitates the use of expensive protein ingredients like soybean meal for meeting the above amino acids requirement.
Dietary requirement of protein in poultry are actually requirements for the amino acids contained in the dietary protein. Amino acids obtained in the dietary protein are used by poultry to fulfill a diversity of functions. In a maize-soybean meal poultry diet, methionine is the first limiting amino acid, followed by lysine, threonine, and tryptophan. Therefore, all these amino acids are supplemented in most practical poultry diets for optimum performance.
Grain supplementation with essential amino acids produced by bacterial fermentation is one of the strategies to meet the requirement. Although, this approach works well for feeding poultry, it is expensive and amino acids often are lost during processing. For these reasons, a genetic enhancement strategy through interdisciplinary and concerted research efforts was adopted to increase this essential amino acids, content in maize and the rebirth of quality protein maize (QPM) took place.
Quality protein maize
Quality protein contains higher protein (>15-20%) than normal maize. Several researchers have demonstrated the superior protein quality and protein digestibility of QPM over normal maize. The studies indicated that QPM contains, in general, 30-40% more tryptophan, 50-60% more lysine and 20-30% less leucine than that of normal maize.
The biological value of normal maize protein (45%) is lower than that of QPM (80%). The apparent and true amino acid digestibility of QPM is higher than normal maize.The other nutritional benefits of QPM include higher niacin availability due to a higher tryptophan and lower leucine content, higher calcium and carbohydrate and carotene utilization.
Faster growth rates
The success of poultry production depends primarily on the quality of the bird, a comforting environment and provision of good feed. Genetic selection for fast growth is a continuous process in the broiler industry and chicks which weigh 40-45 g at day-old are today growing to about 2.0 – 2.2 kg at 40 days.
The fast growth in today’s broiler possesses a challenge to the nutritionist to formulate diets to exploit fully the genetic potential. The diets to be formulated should be high nutrient density diet with well balanced in all the nutrients. The ideal nutrient profile of a practical broiler chicken diet is given in Table 1.
In a study conducted by the authors, dietary replacement of normal maize with quality protein maize resulted in higher body weight gain both at 21 and 40 days of age (see Figure 1). Though feed conversion ratio was not affected at 21 days, however the FCR improved significantly at 40 days of age.
The dressed meat yield and giblet (liver, heart and gizzard) weight were not influenced by the replacement of normal maize with QPM in the diets of broiler. However, abdominal fat content decreased and breast meat yield improved significantly by replacement of normal maize with QPM.
It may be concluded that dietary inclusion of quality protein maize in poultry not only improves performance but also increase the meat yield (breast) in broilers.