As autumn progresses, it is accompanied by cool weather, better milk production and easier reproduction for dairy herds. However, among all the benefits of the season, producers must be mindful of the dangers of feeding forages after a frost. Sudangrass, johnsongrass, sorghum-sudan hybrids, forage sorghum and grain sorghum can all fall suspect to prussic acid or nitrate poisoning.
Prussic acid poisoning is most prevalent following any stress condition that slows plant growth. It's specifically common in plants growing in soil with high nitrogen levels or low phosphorus or potassium. Plants under duress in these conditions release prussic acid when digested in the rumen and absorbed into the bloodstream interfering with oxygen transfer. Animals suffering from this condition die from asphyxiation within minutes.
Nitrate poisoning occurs under similar cool weather, high-stress conditions and results in animals being unable to metabolize high nitrite levels in the blood quickly enough. The resulting symptoms are rapid breathing, fast and weak heartbeat, muscle tremors, staggering and ultimately death.
Maurice Eastridge and Mark Sulc, extension specialists at Ohio State University, suggest several tips for avoiding poisoning while grazing or feeding these late season forages.
- Graze or greenchop only when the grass is greater than 18 inches tall.
- Do not allow animals to graze wilted plants or plants with young tillers.
- Wait four to five days after rainfall before grazing plants after a drought.
- Do not allow animals to graze on nights when frost is likely.
- Wait five to seven days after a killing frost to allow animals to graze.
- Avoid grazing for two weeks after a non-killing frost.
- Delay feeding of silage for six to eight weeks after ensiling.
- Split applications of nitrogen and ensure the proper levels of phosphorus and potassium in the soil to reduce the risk of poisoning.
- Don't allow hungry or stressed animals to graze young sorghum grass growth.
The author is the Special Publications editor. She is responsible for development and marketing of books and plans, as well as coordinating internal communication pieces. Maggie was raised on a 150-cow dairy near Valley Center, Kan. and graduated from Kansas State University with degrees in agricultural communications and animal sciences.
