Warm-season annuals, such as sudangrass, sorghum/sudangrass hybrids, and millets, are useful forages for summer grazing because they flourish when cool season grasses experience “summer slump.” When deciding which of these forages might fit into your grazing system, recognizing the different traits and common uses of each is important. 

The management of these warm-season grasses are not the same as a cool-season grass like tall fescue. The recommended time to harvest these forages is when plants reach 20-24 inches, which will be before seedheads develop. Once plants have been grazed to 8-12 inches, cattle should be removed to provide a rest period for the forages until the height again reaches 20-24 inches (usually 10-20 days). To optimize the use of warm-season grasses, make sure you stock heavy enough to graze the grass down quickly. Ideally, a warm-season grass paddock should be strip grazed. Conduct a yield estimate so each paddock can be designed for cattle to graze down the forage within a day or at most a week, then the animals rotated to another paddock (or electric fences moved), not allowing cattle to back graze the previous area.

The potential of nitrate and prussic acid poisoning is present when grazing annual grasses in the sorghum family such as sudangrass and sorghum/sudangrass hybrids. Nitrate poisoning can occur under conditions such as high nitrogen fertilization, drought, or sudden weather changes. Plants such as sudangrass and sorghum/sudangrass contain cyanide-producing com-pounds that cause prussic acid poisoning, which occurs most commonly during drought conditions, or when the plants are physically damaged (i.e. hail or frost). To prevent these problems, do not graze during or shortly after drought periods when growth is severely reduced, or when plants are wilted or damaged. Not grazing plants too short also greatly reduces the chance of nitrate and prussic acid poisoning in warm season grasses. Rapid screening tests are now available through KY County Extension Agents to ensure the forage is safe to graze.

Below, each species is briefly described with general considerations for each.

Sudangrass can be grazed or harvested multiple times throughout the season and is commonly used for grazing hay, and haylage. This species has a thinner stem, lower lignin content, and higher digestibility in comparison to sorghum.

Sorghum/sudangrass hybrids, often referred to as Sudex, can be harvested multiple times and areas used for grazing, silage, and hay. This hybrid has a thicker stem than sudangrass and lower lignin content than sorghum.

BMR (Brown Mid-Rib) varieties are available for all above species. These have been developed using naturally occurring mutation that results in reduced lignin content and increased digestibility.

Millets, although typically lower yielding, are free of risk for prussic acid poisoning. Pearl millet can be grazed or harvested multiple times, while foxtail millet, which is shorter and finer stemmed, is a one-cut crop. Foxtail millet is ideal for a short-term (50-60 day) hay crop.

"Warm-season annuals are managed quite differently than cool-season grasses such as fescue."

For more information on different varieties, see PR-686: 2014 Summer Annual Grass Report. You can also contact your local county agent or seed dealer to find varieties best suited for you.

Categories: 
Summer
Extending the Grazing Season