Dhurrin-Free Sorghum-Sudangrass Safe for Livestock

By Blake Jackson

Sorghum-sudangrass, a hybrid warm-season annual forage, is valued for drought tolerance and low production costs. It is especially suited for grazing because of finer stems and strong regrowth compared to forage sorghum.

However, the presence of dhurrin, a protein that can convert to hydrogen cyanide (HCN), poses risks for livestock. Known as prussic acid poisoning, HCN toxicity can be fatal to ruminants within minutes.

Concentrations of HCN are highest in young plants but may also spike after environmental stress such as frost or drought, making grazing dangerous at those times.

Although levels eventually decline, producers often remove animals from affected pastures for 10 to 14 days a strategy that helps but creates management challenges.

A new cultivar of sorghum-sudangrass has recently been developed without the gene responsible for dhurrin production, effectively eliminating the risk of prussic acid poisoning. To evaluate this dhurrin-free (DF) variety, Penn State researchers conducted a field study in 2023 at Haller Farm in State College, PA.

Two five-acre plots were planted: one with DF sorghum-sudangrass and the other with a conventional (CON) variety. Both were managed under identical fertilization and harvest schedules, with forage harvested twice, wilted, baled, wrapped, and later sampled for nutritional analysis.

Nutrient results reflected plant maturity rather than variety. The first cutting, harvested later, had lower crude protein (CP) but higher fiber, making it better suited for mature cows. The second cutting offered higher CP and lower fiber, meeting the needs of growing calves.

Nutritional composition between DF and CON was nearly identical, with only slight, biologically insignificant differences in fiber and organic matter. Ruminal disappearance tests also showed no meaningful differences between the two.

For livestock producers, the availability of dhurrin-free sorghum-sudangrass offers a safe forage option without compromising nutritional value. While only one DF variety currently exists, it represents a breakthrough that removes the risk of prussic acid poisoning while maintaining feed quality for beef cattle.