Cotton is one of the largest producing crops around the world. The plant provides cotton fibre as the raw material for the textile industry. The ”byproduct” of cotton harvest is cottonseed and its yield is 1.65 times more than the weight of the cotton produced. Cottonseed consists of 21% oil and relatively high-quality protein (23%). But the cotton plant also has another – unwanted component: i.e. “Gossypol”, which is present in the seed and gets transferred into cake as well as oil after oil extraction. This is a secondary metabolite and serves as a defense compound for the plant due do its bitter taste. The free gossypol gets detoxified in rumen by the formation of gossypol-protein complex. Therefore, its consumption does not cause any harmful effects when incorporated into the diet of adult ruminants. In fact, cotton seed cake serves as a naturally occurring bypass protein for ruminants. However, the non-ruminants are too sensitive to gossypol, which causes toxicity in poultry. However recently, US researchers, at A & M University, Texas, US (Rathore et al, Feedipeia, 2017) have developed a gossypol-free variety of cottonseed.
Toxicity caused by gossypol
Cottonseed as such or cotton seed cake, are both used as a proteineous feed ingredients for ruminants. In fact, it has been reported that feeding of seed as such or the cake increases the fat content in the milk of cows and buffaloes. The toxic principal, viz. “Gossypol” present in the cake gets bound to proteins in the rumen to form a complex. Therefore, its feeding to adult ruminants generally does not cause any toxicity. Sometimes even adult cattle can suffer from gossypol toxicity above a certain level of consumption of cottonseed/ cotton seed cake. Young animals, without fully developed rumen, are more sensitive to gossypol compared to the adult ruminants. However, monogastric animals such as pigs, birds, fish, and rodents are more susceptible to gossypol toxicity.
Biotechnological approach for the elimination of gossypol
Cottonseed and its cake as such has the potential to be used in the diet of non ruminants as well. But before that we have to get rid of the culprit hidden in the seed, the “Gossypol”. The elimination of gossypol could be a boon for cotton-producing countries, which unfortunately are also those, the ones suffering from feed shortage and more specifically protein shortage. After the elimination of the toxin, its seed or the oil cake can be used as a protein source for poultry, swine or aquaculture species. The elimination from the cottonseed has been a long-standing goal of geneticists and cottonseed processors.
In the 90s, biotechnology tools were able to identify the first gene that encodes an important enzyme involved at a critical step in gossypol biosynthetic pathway of the gossypol. In addition, another important component, a DNA sequence that can be used to control seed-specific expression or silencing of a given gene was also isolated from cotton and genetically characterized.
Production of Ultra-low Gossypol Cottonseed
. In the late 90s, the biological community came to understand a natural biological phenomenon known as RNA interference (RNAi) that can also be used to silence a desired gene in an eukaryotic organism. A team at Texas A&M University used a combination of these three tools and technologies to engineer a cotton plant that resulted in the reduction of gossypol from ~10,000 ppm to about 250 ppm in the seed (the United Nations Food and Agriculture Organization and World Health Organization guidelines permit up to 600 ppm free gossypol in edible cottonseed products).
The Ultra-low Gossypol Cottonseed (ULGCS), developed by the US researchers has been further tested in the field as a feed ingredient for non-ruminants. The field results have shown that egg and broiler production could be done most efficiently, using the ULGCS. This news can bring cheer to Indian feed, poultry, pig and aqua industries, which is reeling under shortage of protein feeds. India being the biggest cotton producer in the world is also experiencing increasing consumption of eggs and poultry, and also fish. ULGCS has shown the promise as fishmeal replacement. This has been recently demonstrated in the diets of shrimp and juvenile Southern flounder by Richardson et al., 2016 and Alam et al., unpublished. Texas A&M University is planning additional aquaculture and poultry feeding studies to fully evaluate the nutritional value of ULGCS.
The author is not the part of the A&M Texas University Research Group, but has modified the original paper, to suit the TGTF readership
Tej K. Walli , BENISON Media