Death by cyanide! Cattle case alarming
TheTexas farmer was alarmed. Never before had he heard his cows bellow in this fashion. He rushed out to the pasture to see what was happening only to be confronted by a horrific scene. His previously healthy animals were either staggering around or writhing on the ground. Eventually 15 of the 18 cattle in the field would perish. The veterinarian who conducted the necropsies concluded they had been poisoned by cyanide! The culprit, as it turned out, was the grass the cattle had been grazing on, a hybrid of two other grasses. It contained “cyanogens,” compounds capable of releasing cyanide! So much for the facts. Now for some butchering of the same.
The world first heard about the cattle catastrophe in June from a CBS correspondent in Elgin, Texas, who, to the obvious delight of the anti-gmo crowd, filed a report under the headline Genetically Modified Grass Linked to Cattle Deaths. Before long, a herd of bloggers and journalists piped in with alarmist stories about how Genetically Modified Grass Kills Cattle By Producing Warfare Chemical Cyanide. But they were too quick on the trigger. They had not done their homework. The grass in question was not genetically modified, at least not in the fashion that activists worry about. It was a hybrid grass, a product of traditional cross-breeding, and was in no way a novel product, having been around since 1983. It was, however, for some reason, in this particular pasture, producing an unusually large amount of cyanide.
Production of cyanide by plants is not a rare phenomenon, with more than 2,600 species capable of releasing the toxic substance having been identified. Within the plant, cyanide is stored in an inactive form, bound to a sugar molecule, ready to be released as hydrogen cyanide upon reaction with an enzyme, stored separately in the plant’s tissues. The inactive compound and the enzyme are brought together when the plant is damaged, for example, when feasted upon by hungry insects. A whiff of cyanide and the insect is highly motivated to satisfy its hunger elsewhere. It seems these plants have evolved a mechanism to protect themselves from predators. And sometimes cattle, or even humans, can suffer the consequences as the plant unleashes its chemical defence system.
Perhaps the best example of the effect of cyanogens on humans is cassava, a staple for millions of people in Africa, South America and Asia. Like a potato, cassava’s tuber-like roots can be boiled, fried or processed into flour. The plant is easy to grow, is drought-resistant and grows well without fertilizer. But it harbours a good dose of the cyanogen linamarin. If not properly processed to rid it of cyanide, cassava can cripple or even kill. Thousands of children in Africa are victims of “konzo,” an irreversible paralysis of the legs caused by ingesting cyanide. Countless others suffer from headaches and dizziness caused by low-grade cyanide poi- soning. Drying, soaking in water, rinsing and baking results in the cyanide being released into the air as hydrogen cyanide, but the process requires time. During periods of famine, there is a tendency to shortcut procedures and consumption of the improperly processed cassava can have tragic results.
If linamarin were to be eliminated from cassava, the time-consuming processing would not be needed. With the aid of genetic engineering, this is a distinct possibility. The gene that codes for the production of linamarin has been identified, and a method to silence it by interfering with the messenger RNA through which it sends out its information has been developed. Silencing cannot be total since some linamarin is needed by the plant to protect it from predators. But studies have shown that most of the linamarin is produced in the leaves, from where it is ferried to the roots. Reducing leaf linamarin content by 40 per cent still leaves plenty for protection and virtually eliminates the cyanide-producing compound from the roots. Further field trials are needed to ensure that inhibition of linamarin formation does not affect crop yields because cyanide is a source of nitrogen and linamarin may be important in its transport from the leaves to the roots of the growing plant.
Yet another way of genetically modifying cassava might reduce its cyanide content. Cassava is quite low in protein, but its content can be boosted by incorporating genes from sweet potatoes or corn that code for the production of a protein called zeolin. Enriching cassava with zeolin could save millions of children from potentially fatal protein-energy malnutrition. Furthermore, it turns out that cassava uses its natural supply of cyanide to produce the amino acids needed to build the new protein, thereby reducing the risk of cyanide toxicity. Again, further testing is required to ensure that the incorporation of the sweet potato or corn genes causes no untoward changes. But the possibility of saving human lives through genetic modification doesn’t get as much play in the press as the demise of a few cows whose deaths have been wrongly attributed to genetically modified grass by a bunch of bloggers and reporters who came across a story that was too juicy to check properly.
So what did happen in that Texas field? The hybrid grass does contain the cyanogen dhurrin, that is a fact. Why this grass that has long been used in cow pastures should all of a sudden produce lethal amounts of cyanide is not clear. Cyanide content is known to vary with growth, with the highest concentrations usually found in seedlings. Stress brought on by drought can lead to cyanide release, as can the use of nitrogen fertilizer at the wrong time, and the grass in the Texas pasture is known to have been heavily fertilized. Curiously, many other farms in the area grow the same kind of grass and have not experienced any problems. At this point, the only thing we can say for sure is that the cattle tragedy had nothing to do with genetically modified organisms. Obviously, nature can do plenty of damage without any help from humans.
Joe Schwarcz is director of Mcgill University’s Office for Science and Society (mcgill.ca/oss). He can be heard every Sunday from 3-4 p.m. on CJAD radio. joe.schwarcz@mcgill.ca