Forage and livestock producers should remain vigilant moving forward in the grazing season due to the potential of Prussic Acid poisoning and Nitrate toxicity in ruminants. When our seasons shift from cool and wet to hot and dry, our forage plants can become stressed. This is even the case when we receive sporadic rains during extreme heat, cloudy days, or wide temperature variations.
Prussic Acid poisoning is most prevalent from sorghum family plants: Sudan grass, sorghum Sudan, millet, and Johnsongrass. Prussic Acid is released in the rumen and readily absorbed into the blood stream and blocks the utilization of oxygen. The concentration of prussic acid is higher in the leaves than the stalk, and the younger top leaves will have higher levels than older leaves on the bottom of the plant. In almost every instance in Logan County, these forages are grown as a dryland crop, which tends to increase the levels of prussic acid in plants.
If your forage is high in prussic acid, there are a few steps you can take to ensure no harm comes to your livestock. Initially, you can utilize a conditioner or crimper when cutting the forage and allow it to fully sun dry. This crimping action and curing reduces the prussic acid through evaporation. If you are utilizing standing forage, don’t turn hungry cattle in on the pasture, and discourage selective grazing. Allowing the forage to grow to 18-20 inches tall will allow for some dilution in the plant. And finally, refrain from excessively applying nitrogen fertilizer.
The second forage issue to watch for is nitrate toxicity. In some respect nitrate toxicity is similar to prussic acid poisoning, but there are different signs to look for. Nitrate toxicity presents due to rumen microbial fermentation, whereas prussic acid poisoning is initiated by the mechanical chewing of the forage. Both result in asphyxiation of the animal in the end.
From the forage standpoint, the two issues are very different and must be managed differently. We find that nitrates are higher in the stalks of the sorghum family plants, instead of the leaves, and the greatest concentration is contained within the lower 6 inches of the stalk. Also, immature plants have a greater potential for nitrate accumulation than older plants. It is important to point out that the biggest difference between the two disorders is that nitrates remain in the plant; very little, if any, will dissipate over time. One successful method of decreasing the amount of nitrate in forage is by ensiling: by microbial fermentation the nitrates are consumed.
When managing a high nitrate forage, keep a few tips in mind. Cut forage six inches off the ground, and refrain from cutting until just before the formation of a seed head. Don’t turn hungry cattle in on questionable pasture, and waiting a few days to cut hay can also make a big difference.
If you have questions about nitrate toxicity or prussic acid poisoning, please contact Brandon at the Logan County Extension office by calling 282-3331. Forage can be field tested for the presence of nitrates and prussic acid for free. Additional laboratory testing can be conducted on forage if nitrate is detected.