Purdue-developed sorghum safer for grazing animals and takes stress off producers

“Sorghum is a great option for forage, but farmers have always had to be really careful about it,” said Tuinstra, Purdue’s Wickersham Chair of Excellence in Agricultural Research and scientific director of the Institute of Plant Sciences. “Removing the dhurrin from the plants takes away that worry. Animals aren’t going to suffer if they eat it at the wrong time. And it’s possible that livestock producers in more areas will be willing to use sorghum as a forage, which would be helpful as the climate changes since sorghum is more heat- and drought-tolerant than some other plants.”

THE FIRST FREEZE

Livestock producers who use sorghum and sorghum-sudangrasses as forage for their animals are acutely aware of the coming of the fall or winter’s first freeze. At that point, many of them abandon the forage and turn to other feed options.

That’s because of dhurrin, whose role in plants is unclear but may provide defense against insects. As temperatures become cooler, this secondary metabolite is thought to accumulate in sorghum leaves and stems, which increases the risk for livestock.

Producers want to get as much out of their forage as possible, since once the forage sorghum is thought to be unsafe, they have to spend money on other feed for their animals. It’s thought that two weeks after a freeze, the sorghum is safe again. However, many producers won’t risk and don't have the time to bring their animals back to the pasture.

Complicating the issue is that it isn’t always clear when livestock should be pulled from a pasture. A light freeze may or may not induce dhurrin accumulation, and the uncertainty can cause producers to abandon the forage and start unnecessarily paying for other feed.

Heat and drought conditions can also lead to dhurrin accumulation, and those are even more difficult to gauge.

“Producers have to play a bit of a guessing game, and many aren’t comfortable doing that. We advise them to plant other forage options, but those aren’t always as productive as sorghum,” said Keith Johnson, a Purdue professor of agronomy and a forage specialist. “Without dhurrin, we can continue to graze much later into the year and not have to worry about it at all. It gets rid of the hassle and fear factor.”

I THOUGHT THEY WERE JOKING

Tuinstra, whose work involves harnessing genetic resources for crop improvement, thought it could be possible to modify sorghum’s DNA to disrupt the biochemical pathway that leads to dhurrin production. He treated sorghum seeds with ethyl methanesulfonate, a compound that produces random mutations to DNA.

The process yielded 12,000 different mutant sorghum lines. Graduate and undergraduate students screened more than 50,000 plants from this population to identify genotypes that do not produce dhurrin. Genomic sequencing identified the gene that was altered and allowed Tuinstra to create experimental hybrids that could be field tested.