Importance and limitations of existing maize as grains
At global level, maize accounts for 15% of proteins and 20% of calories in world food diet. In India maize (Zea mays L.) is the third most important cereal after wheat and rice. Currently it is cultivated over 8.12 million ha with 19.77 million tonnes production with an average productivity of 2435 kg/ ha, contributing nearly 8 % in the national food basket. Maize occupies an important place as a source of human food (25%), animal feed (12 %), poultry feed (49%), industrial products mainly as starch (12%), and 1 % each in brewery and seed.
Unfortunately maize grain has two significant flaws; it lacks the full range of amino acids, namely lysine and tryptophan, needed to produce proteins, and moreover, the niacin (vitamin B3) present in the grain is bound as an indigestible complex. Earlier, the people used to boil maize in the alkaline limewater which would break down the complex so that the Niacin became available. However this practice did not transfer to the Old World or settlers in the “New World” which had earlier resulted in epidemics of Pellagra from the 16th century onwards. In addition, diets high in corn produce a condition known as wet-malnutrition – a person receiving sufficient calories, but her or his body malfunctions due to a lack of protein or protein energy imbalance. A chronic lack of protein in the diet leads to kwashiorkor.
In normal maize grain, the quality of protein is poor due to the presence of largest concentration of alcohol soluble protein fraction ‘prolamine’ also known as ‘Zein’ in the endosperm. Zein is very low in lysine and tryptophan content. Since this fraction contributes more than 50 per cent of the total protein, the protein of normal maize grain is low in lysine and tryptophan content. On the other hand, zein fractions contain very high amount of leucine and imbalanced proportion of isoleucine. On the whole, the lack of proper proportion of all these four essential amino acids results in the poor quality of protein in normal maize. The high quality of protein in other fractions in other parts of maize kernel becomes recessive due to the dominance of zein in normal maize. Thus, the poor quality of protein in normal maize affects its ‘Biological value’ i.e. the availability of protein in the body. Because, the lysine, tryptophan and threonine are the limiting amino acids in human beings and non-ruminants. In the absence of limiting amino acids the other amino acids are either deaminated and excreted (increasing the stress on animal) or used as energy source.
Development of Quality Protein maize
Surinder Vasal and Evangelina Villegas began their collaborative research at CIMMYT integrating cereal chemistry and plant breeding techniques. They produced a QPM germplasm with hard kernel characteristics and good taste similar to the traditional grain and with much higher quality levels of lysine and tryptophan. Quality protein maize looks and tastes like normal maize with same or higher yield potential. Besides increased biological value; QPM has additional nutritional advantages, such as higher concentration of niacin (vitamin B3) and improved absorption of potassium and carotene. In India, through acclimatization and repeated selection, hard endosperm modified opaque-2 maize inbred lines and their crosses have been identified for better protein quality and higher yield potential.
Nutritive Value of Quality Protein Maize (QPM):
The normal maize grain under Indian conditions on an average, contains 14.9 % moisture, 11.1 % protein, 3.6 % fat, 2.7 % fibre, 66.2 % other carbohydrates and 1.5% minerals.
The True Protein Digestibility of normal maize and Quality Protein Maize is almost same, but the biological value of normal maize is just half as compared to that of QPM varieties. Rather, the biological value of QPM is highest among all the food grains owing to the reason that all cereals except QPM are deficient in lysine, an essential amino acid and all pulses are deficient in methionine, the other essential amino acid.
There are no significant differences in gross energy (GE), apparent metabolizable energy (AME) (poultry) and apparent digestible energy (ADE) (pigs) between QPM and NM. Although NM has a higher GE content than QPM, its AME for poultry and ADE for pigs are lower than those of QPM. It indicates that the energy available from QPM is little higher than that from NM.
Value of high-lysine cereals (QPM) in animal nutrition
A variety of animals have been used in demonstrating the superior performance of QPM compared to normal maize used alone or in combination with different food rations. It is fair to say that QPM has great potential in monogastric animals such as rats, chickens and swine. Other advantage and role of QPM could be seen in substituting it for high protein costly supplements like soybean or fish meal.
Feeding trials showed that rats fed on opaque-2 compared with normal maize exhibited a three to six fold increase in body weight. They also exhibited better feed intake and feed conversion efficiency in chickens. In poultry feeding some special considerations must be kept in mind. Growing chicks need high protein and high methionine content diets. With only methionine supplementation, the opaque-2 fed chickens grew faster than those fed on normal maize, and produced better live weight gain and feed conversion, even at below optimal protein levels. The feed efficiency ratio for QPM and normal maize was 3.5:1 and 8.2:1 respectively. From limited studies in Asia, one may conclude that QPM has great promise for feeding poultry if supplemented adequately with methionine.
Field demonstrations of QPM on swine have produced striking and convincing results. For swine, QPM can be fed as the only source of protein during finishing, gestation and pre-gestation periods without reducing growth. In some experiments, pigs fed QPM grew 3.5 times faster than on normal maize when maize was the sole protein source. Since protein in QPM is not concentrated, it is advisable to add or mix with some supplement. It is recommended that for growing pigs of all ages or lactating sows, opaque-2 maize must be supplemented with extra protein to produce optimum performance. The dramatic effects of feeding QPM to non ruminant livestock have been demonstrated in other countries such as Guatemala, China, Vietnam and Kenya.
In White Leghorn layer chicken diet feeding value of quality protein maize (QPM) was superior to normal maize (NM), whereas that of Nityashree hybrid maize (NHM) was similar to NM. Quality protein maize-based layer diet produced 3.3% higher egg production and recorded 4.9% improvement in feed conversion compared to NM. Substituting QPM for regular maize in the production of broiler feed reduces the amount of expensive protein sources used, leading to a cost reduction of 5%. Optimal ratios of QPM and regular maize were calculated and diets formulated, and subsequent trials showed that broilers raised with either mixture had the same feed intake, mortality and growth rates.
Contribution to protecting the environment
Nitrogen excretion due to animal farming is posing a serious threat to human health through ammonia or nitrate/nitrite pollution in soil and water. Farmers now must therefore face more and more stringent environmental regulations. Decreasing excessive protein in feed by supplementation of amino acids is the most cost-effective way to solve the problems of nitrogen pollution associated with animal feeding. It is a preventive measure aimed at reduction of pollutant output at its source. On an average, reduction of crude protein content in a diet by one percentage point can yield about an eight to ten percent reduction in nitrogen excretion. Reducing the crude protein level by three to four percent, with supplementation of first, second and third limiting amino acids, will yield at least the same growth performance but with around 20-30 percent reduction in nitrogen excretion.
The projections of International Food Policy Research Institute (IFPRI) has indicated that there will be 85 and 45 % increase in global demand for poultry and pork during 25 years (between 1995 and 2020) for which maize is the major source of feed that indicates growing demand for maize globally. In India the average per capita egg consumption is also increasing at fast pace.
Export markets are also likely to open up as subsidies on agricultural products are phased out internationally under World Trade Organization (WTO) agreements. By making the quality and cost of eggs and poultry meat competitive, the Indian poultry sector is expected to capture a significant share of the export market currently dominated by the United States, Brazil, Netherlands and Thailand. India has already started exporting shell eggs to gulf countries and egg powder to the European Union (EU) and Japan. India also exports large quantities of hatching eggs to Bangladesh, Singapore, Maldives, United Arab Emirates, Saudi Arabia and Oman and specific pathogen free eggs to the EU for pharmaceutical purposes.
Consumption of commercial feed by the poultry sector at present is 28 million tonnes/year. The poultry industry is highly dependent on the feed industry, which is only 35 years old. The Indian feed industry caters predominantly to the dairy and poultry sector. At present, the Indian organized feed industry produces around 3 million tonnes of feed/year, which is only 5 percent of its actual potential. It is more economical to use diets incorporating QPM as it can lead to progressive reductions in the use of fishmeal and synthetic lysine additives.
A WORD OF CAUTION WHILE USING QPM
a. The lower digestibility of methionine with QPM should be notified if it is used in animal feed because methionine is one of the most limiting amino acids in animal feeds.
b. opaque-2 is a recessive gene and an invisible trait, which makes it harder to maintain during breeding, seed production or while recycling seed under farmers’ conditions. Therefore, special attention needs to be paid to training maize breeders, seed producers and farmers in appropriate manipulation of QPM in order to preserve the trait in the seed of future generations.
c. The industry would need a way of assessing the quality of the QPM it purchased. Therefore, a local laboratory provided at reasonable cost is needed to analyse maize for its amino acid content
d. The database for utilization of QPM in livestock, poultry and fishes is scanty especially in dairy animals, Hence the recommendations with possible economic benefits to owners cannot be formed
The expanded demand for meat and other animal products has witnessed unprecedented growth in livestock sector, which is now spilling over to feed industry as well. In the next two decades the growth of livestock sector is likely to continue at the rate of 33 percent per year. The demand for feed will thus rise rapidly and will have to be met by cereals which have potential for increased productivity and improved nutritional value through better feed efficiency. Maize will certainly play a dominant role, and QPM will have the added advantage of being superior in protein quality and higher in feed efficiency.
QPM as a livestock feed need to be exploited along with the following activities:
1. Motivation of farmers for more QPM cultivation
2. More research reports on long term and short term effects on different categories of livestock on productivity
3. The economics of oilseed cakes replacement, comparison with protected/ unprotected amino acids supplementation should be worked out.
4. Easy and cost effective availability of QPM quality confirmation mechanism
by Nitin Tyagi and Rakesh Kumar, ICAR- National Dairy Research Institute