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Watch Out for Prussic Acid !!
This is the time of year cattle producers need to be careful of Prussic acid. Prussic acid poisoning may occur when livestock consume certain forages and wild plants. Prussic acid is also called hydrocyanic acid or HCN. HCN can build up to toxic levels in leaves of plants such as Johnsongrass, sorgum, sudangrass, sorghum-sudan hybrids and wild cherries.
There have been many questions about grazing sorghum. Grazing susceptible forages may be very dangerous. This is because cattle prefer grazing young leaves and shoots which could be high in HCN or Prussic acid. Also this time of year producers have to be careful. The reason for this is that any condition that alters normal plant growth including drought of frost will usually cause higher levels of HCN.
Here are some other things to keep in mind.
1. Higher nitrogen rates will increase HCN potential.
2. There is more HCN in the leaves than in the stems. The topmost younger leaves contain more HCN than do the lower leaves.
3. Younger plants contain more concentration of HCN than older plants.
Here are some guidelines for avoiding Prussic acid poisoning.
1. Do not turn in hungry cattle. Feed some hay first then turn in cattle in late afternoon.
2. Follow fertilizer recommendations to assure adequate soil phosphorus. Avoid high levels of nitrogen.
3. Forage sorghums may not be safe for grazing until headed out.
4. Allow plants to reach at least 18 to 24 inches in height before grazing. HCN is present in large amounts only in the rapidly growing portion of the plant.
5. Use EXTREME CATION when allowing animals to graze after frost. A light frost may only kill the tops of plants. New shoots may develop which are high in HCN and these new shoots are preferred by livestock.
6. Plants that is safe to graze before the frost (above 18 inches or headed sorghum) can be safely grazed 7 to 10 days following a killing frost.
7. Plants that were too short for safe grazing before a killing frost should not be grazed for at least two weeks.
8. If you are not sure call someone who knows.

How much nitrogen to apply to my winter grazing?  If you have cool season annual forages, apply 40 to 50 lbs. of nitrogen (N) per acre at planting or soon after the plants emerge to increase growth, tillering (thickening of the stand), and provide earlier grazing. A second application of 40 to 50 lbs. of N per acre should be applied in mid-winter to increase winter and spring forage production. If you have ryegrass in your forage program then  a third application of 40 to 50 lbs. of N per acre may be needed in early spring.

When can I start to graze my winter forages?  Grazing is one of the best uses for cool season annual grasses; however, the species differ somewhat in their tolerance of grazing. Ryegrass and rye are generally very tolerant of repeated grazing, while triticale generally does not regrow quickly. Barley, wheat, and oats have poor grazing tolerance.

Grazing can begin as soon as the plants are well-established and have accumulated four inches (or more) of growth. Begin with a light stocking rate and gradually increase as the growing conditions improve and forage growth rate increases. Consider the forage quality, nutritional needs of the animals, amount of forage present, availability, and the cost of other feed items when deciding how many animals to graze. Restricting the animal’s time on the paddock, rotating animals between paddocks, or using strip grazing techniques will improve utilization and reduce damage to the stand. Grazing when the soil is too wet (when animals’ hooves can bog in the soil) can severely damage winter annuals and will decrease potential production.

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