Hay there everyone! This article appears in CropWatch and was reviewed by Ben Beckman, UNL Beef Extension Educator and UNL Forage Specialist Bruce Anderson. I wanted to post it again following our cold weekend weather!
Freezing temperatures are on their way for most of Nebraska. These freezing temperatures will play a key role in determining what can be grazed or hayed safely for your livestock. With many of Nebraska’s acres in cover mixtures due to preventive planting, taking a quick check before grazing or utilizing mixes is key. These mixes may be unfamiliar or new to our system and could be hazardous when fed incorrectly. Freezing temperatures cause metabolic and cellular changes to our forage crops. Nitrate poisoning and prussic acid formation are the biggest concerns.
Sorghum, sudangrass, sorghum-sudangrass hybrids, and milo following a frost have broken cell membranes that allow the formation of prussic acid. Prussic acid is a form of cyanide that can quickly cause lethal results when consumed in high amounts. Monogastric species like pigs and horses can get prussic acid poisoning in extreme cases, but ruminants are more susceptible. Keeping livestock out of these areas for 5-7 days following a frost can limit the risk associated with prussic acid. Each time a new part of the plant is frozen, this 5-7 day timer is reset.
New shoots and especially regrowth on previously frost damaged plants has the highest concentrations of prussic acid. If you notice new shots after a frost, animals should not be allowed to graze until the regrowth is 15-18 inches tall or until a frost completely kills the plant. With warmer temperatures set to follow the cold this weekend, keeping an eye out for these new shoots is going to be particularly important this fall.
Unless extremely high levels of prussic acid are present initially, haying or cutting prussic acid is not a concern. During the drying process the prussic acid to volatilize and 50% or more of initial concentrations are lost. If you are concerned about high levels of prussic acid in a silage or hay feed, samples can be sent to a lab for analysis. Below is the relative risk for prussic acid formation adapted from The Ohio State University.
- Sudangrass varieties = low to intermediate
- Sudangrass hybrids = intermediate
- Sorghum-sudangrass hybrids and forage sorghums = intermediate to high
- Grain sorghum = high to very high
*adapted from Mark Sulc, The Ohio State University.
Grasses are especially susceptible to nitrate poisoning risks. Slower metabolism following a stress like freezing allows nitrates to accumulate within the plant, specifically oats, sudangrass, and millets. Haying or green chopping is not recommended following a freeze and can be potentially dangerous. Nitrates commonly concentrate in the lower portions of plant stems. Waiting five days before haying or chopping and keeping a cutting height between 6 to 8 inches will help mitigate risk. If grazing, reduce stocking rate and increasing the animals ability to selectively graze can lower nitrate risks. This is not a good strategy for mixtures with sorghum species due to the prussic acid concerns we discussed above.
One final issue to keep an eye out for following a freeze is bloat. In high quality forages like alfalfa, clover, and fresh small grain shoots, frost damage in the plant will rupture cell walls and make protein and minerals more readily available for 1-2 days. These readily available proteins and minerals increase gas buildup in the rumen to the point where animals cannot eliminate them by eructation (belching) and we have bloat.
Fresh young plants and naturally higher protein species like legumes have a higher chance of causing bloat. In cover crop mixtures, grazing mature plants will help lower this risk and making sure that mixtures don’t contain more than 50% high forage quality species like clover and alfalfa. Providing free choice grass hay and limiting animal grazing by strip grazing so a more balanced mixture of plants are consumed can be used to decrease the likelihood of bloat even further.
The bottom line is to be patient when utilizing these forages.
- With haying and cutting, prussic acid is not a concern, but nitrates can be worse. Remember wait five days before cutting and to raise cutting height to 6 to 8 inches to reduce risk.
- With grazing waiting five to seven days after a hard frost can limit risk for both nitrate and prussic acid poisoning. Keep an eye on high quality forage mixtures for bloat potential and pull off for 1-2 days after a frost to minimize risk.
Have a great week and stay safe during harvest!
Thanks and join me next time for more Crop Talk!
Megan T
Special thanks to Ben Beckman and Bruce Anderson for reviewing! Also check out CropWatch for updates from across Nebraska!
Crop Talk Megan 