The most commonly exploited trait in GM crop is the herbicide tolerance. This trait has been exploited in corn, soybean and cotton. These plants have been developed in the United States and in the year 2002 more than 75 % soybeans, 60 % cotton and 10 % corn, which were genetically modified for herbicide tolerance, are under cultivation. Monsanto a multinational has developed Roundup ready brands for soybean and canola. AgrEvo USA has developed a liberty link brand for soybean and rice. Herbicide tolerance plants provide the farmer the flexibility to apply herbicide whenever it is needed, establish weed control programmes with no till or reduced till farming to prevent soil erosion. Chine and Re (1997) reported that Round up ready soybean growers reduced herbicide use by 9 % in US east central region and 31 % in US south central region. Pest pressure and related crop damage vary greatly from region to region and even across individual location. But recently there have been reports that herbicide usage in US alone has come down by 40 to 50 %.
Insects damage crops in the field, which lead to tremendous loss to the farmer. Insect resistant plants could be produced by introducing BT proteins from Bacillus thurigenesis into crops like corn, Soya etc. Bacillus thurigenesis is a natural occurring bacterium in the soil that produces a protein that controls insects by disrupting the insect’s digestive system. The BT protein has been found to be harmless to humans, fish, wildlife and beneficial insects. The benefits of having a BT protein in crops would lead to less dependence on chemical insecticides. In this way it would also protect the grower from being exposed to insecticides. There would also be a reduction in the accumulation of these chemicals in ground water. BT protein could also be utilized in controlling mycotoxin and aflatoxin problems in feed grains (Lipps et al., 1986), which are very relevant to hot, and humid climates like India. It is well known that mycotoxin contamination reduces growth efficiency, lowers feed conversions and reproductive rates, impairs resistance to infectious diseases and induces pathological damage to the liver and other organs. Several multinational companies like Pioneer Hibred international, Northrup King, and Monsanto etc have developed some of these varieties and in the coming years India would greatly benefit from such varieties.
There is also scope for producing disease resistant crops, which take a devastating toll on crops like corn, rice etc. Presently there is no commercially available cereal or legume genetically modified grain that is considered disease resistant. Biotechnology can also help increase crop’s ability to withstand natural environment factors such as heat and drought, soil toxicity, high salinity etc and hence improve farming in regions in which the crop is difficult to grow. For example threalose, a glucose disaccharide when introduced into rice could stand stress conditions of high salinity, drought and low temperature without affecting any other nutritional balance (Garg et al., 2002). GM plants could also be used to deliver edible vaccines through corn or soybean. This could reduce the dependence of cold chains to preserve vaccines, a difficult task in tropical countries like India, especially in remote areas.
Some of the limitations which the nutritionist face during feed formulation are the antinutritive factors like trypsin inhibitors, saponins, tannins, phytates, oxalates, high fiber, limitation of phosphorus content etc in grains. Developing genetically modified grains having improved nutritional values could solve these problems.
Low phytate corn: All plant feed ingredients contain natural phosphorus, which is only 30 % available, and the rest 70 % is in the form of phytate phosphorus. If grains with low phytate phosphorus and high available phosphorus were made available the use of supplemental inorganic phosphorus like dicalcium phosphate in poultry would come down (Stillborn & Crum., 1997). This would not only reduce the cost but also high quality, bioavailable phosphorus would be made available to the birds. The added advantage is that less phosphorus would be thrown in the litter and manure, which would lead to the control of eutrophication. This problem is not observed in ruminants because their digestive tract is more efficient in utilizing dietary phosphorus.
Broiler feeding studies with low phytate phosphorus and conventional corn showed that low phytate phosphorus corn was biologically more available based on increased bone ash, bone phosphorus and bone calcium compared to the phosphorus from conventional corn. There was a significant decrease in the fecal phosphorus when low phytate phosphorus corn was used (Table 2) The low phytate phosphorus corn cultivars contain approximately 35 % phytate phosphorus and 65 % of non-phytate phosphorus, which was reverse in commercial corn (Li et al., 2000).
High oil corn: Research on production of high oil has been going on for a long time. Araba (1997) reported that high oil corn varieties were produced using traditional genetic breeding, which contained 6–8 % oil, but the yield was low compared to commercial varieties. Now Dupont has come out with a brand called OPTIMUM 80 high oil corn through genetic modifications. This variety contains 87 % higher crude oil fat and 3.3% higher crude protein compared to typical corn.
Feeding studies with high oil corn on broilers showed that there was a significant improvement in body weight and feed conversions (Engelke., 1997, Lee et al., 2001) . The broilers fed on high oil corn contained less abdominal fat, compared to broilers fed conventional corn and comparable levels of poultry oil. Yan et al. (1987) reported that hens fed on high oil corn diet had a better feed to egg ratio. The egg yolks when analysed contained increased levels of linoleic acid and oleic acid.
Low oligosaccharide soybean: Soybeans contain raffinose and stachyose the oligosaccharides, which act as antinutritive factors (Coon et al., 1990). Oligosaccharides are known to cause osmotic carthisis in lab animals. Companies like Dupont have already developed genetically modified soybeans with low oligosaccharides. These cultivars gave an increase of 3% in amino acid digestibility and 5 % increase in dry matter digestibility (Leske et al., 1995). Soybeans with high lysine are also being developed to increase the lysine content from 3 % to 4.5 % (Table 3) and this would reduce the supplemental addition of lysine in diets and the same could be done with corn.
GM crops with improved amino acid profiles have great potential to decrease nitrogen excretion in poultry. Nitrogen can contaminate ground and surface waters; contribute to acid rains, which increase the acids in soils. Increased levels of essential amino acids like lysine, methionine, tryptophan, threonine in grains would mean that the essential amino acid requirement of poultry can be met with lower protein diets. Feeding these GM varieties would reduce the amount of nitrogen in the form of urea from being excreted into the environment.
The inclusion of genetically modified feedstuffs in animal feed could also pose certain risks. GM plants are produced by transferring foreign genes of particular characteristics into feed grain crops. For example introducing antibiotic resistant marker genes may render common infectious diseases untreatable or certain proteins may cause allergic reactions to animals and humans. Hence proper lab, field assessments as well as health assessments have to be made before release of such plants for commercial cultivation.
