New Sorghum Sudangrass Variety Shows Promise
Published: Friday, November 26, 2021
Purdue University researchers are working on a new variety of sorghum sudangrass that would give cattlemen the ability to continue grazing their animals after the season's first frost. The innovation in plant breeding is described by a Purdue University Extension beef specialist as a "game changer" for both beef and dairy producers.
Ron Lemenager, Purdue University Extension beef specialist, is excited about the new line of dhurrin-free sorghum sudangrass being developed at the West Lafayette campus in partnership with a commercial plant breeder.
Sorghum sudangrass is a popular cover crop that grows well in the hot, dry conditions of summer. Beef producers often turn to it as a source of roughage and fiber in cattle diets. However, the warm-season grass can become toxic after the first frost.
After a frost or freeze, sorghum sudangrass produces high concentrations of dhurrin, which can lead to cyanosis, or prussic acid poisoning, in the animals consuming it. Lemenager says the standard advice is to wait seven to 10 days before allowing cattle to graze again.
The dhurrin-free variety eliminates that worry. In the Midwest, this new forage would allow cattle and dairy producers to feed sorghum sudangrass throughout the summer and fall.
A team of researchers, led by Mitch Tuinstra, professor of plant breeding and genetics at Purdue, began work on a dhurrin-free variety nearly 12 years ago. Tuinstra's team was able to identify a genetic mutation that essentially shuts down the production of dhurrin in the plant. They were able to secure a patent on the research, and developed an agreement to bring it to market.
Four years ago, Shelby Gruss, then a Ph.D. student and now a post-doctoral scholar, joined the team. This summer, she oversaw the performance trial at Purdue's Scholer Farm as part of her doctoral project. The goal of the trial, featuring both commercial and dhurrin-free lines, was to see how well beef calves could gain weight while grazing on paddocks planted with dhurrin-free sorghum sudangrass.
"What we found was the dhurrin-free line was consistent with the conventional market hybrid, and we did not see any negative impacts of using a dhurrin-free line in comparison to the conventional hybrid," she said. "Weight gains were about 2 pounds per day on the dhurrin-free line, and weight gains on the conventional lines were 2.1 pounds per day, which was not a significant difference at all."
The performance trial lasted 64 days, providing useful data on the cattle's weight gain. After the trial ended, Gruss continued to monitor their performance after the first frost of the season.
"We had three calves on the dhurrin-free hybrid for about a week and a half after the first frost occurred," she said. "The way the first frost occurred this year was—I think we had a frost on a Thursday. It was kind of a lighter frost but we still had frost damage on the leaves. And then the following Monday, Tuesday, Wednesday, Thursday, we had significant frost damage occur each of those dates until the plants were dead.
"So, we did not see any negative effects from leaving our cattle on the dhurrin-free hybrid. They were able to graze it freely without any prussic acid poisoning."
A previous trial conducted in 2019 and 2020 showed that grazing animals—in this case, sheep—have a preference for the dhurrin-free hybrid.
"They would graze it to the ground before they started grazing other sorghum sudangrass options," Gruss said.
Based on these trials, Gruss said she has a high confidence level that this new forage product will become the preferred variety for cattle and dairy producers.
She added that the dhurrin-free variety could be a good option to use after the wheat crop comes off, in a double-cropping system.
"It can really extend your (grazing) season," Gruss said.
Also working on the project are plant breeders with S&W Seed Co., with whom Purdue has a licensing agreement.
Lemenager said dhurrin-free sorghum sudangrass has the potential to be a "game changer" for livestock producers, especially in summers with little rain. Their goal is to insert the dhurrin-free trait into any existing variety.
"If we can increase the digestibility of the seed, particularly of the protein fraction, and bring the performance up to corn silage, this would be a real significant breakthrough from the standpoint of drought tolerance."
Producers could graze sorghum sudangrass or harvest it like corn silage, but the main benefit would be what it could provide after a frost.
The dhurrin-free variety is not commercially available yet. Lemenager anticipates that happening sometime in the next couple of years.
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