NDSU Extension - Stark & Billings County

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NDSU Extension Offers Tips for Fall Grazing Cover Crops

Cover crop acreage is expected to increase in response to the U.S. Department of Agriculture Risk Management Agency's revision to the preventive-planting insurance provisions, according to North Dakota State University Extension livestock experts.

The revision has allowed producers to hay or graze a cover crop on preventive-plant acres beginning Sept. 1. This increase in cover crop acreage provides an opportunity for ranchers.

 

"Cover crops are a great way for ranchers to add flexibility into their grazing system," says Miranda Meehan, Extension livestock environmental stewardship specialist. "Planting cover crops will produce a high-quality forage and extend the grazing season while allowing rangeland and pastures adequate time to recover."

 

However, grazing cover crops can present some challenges to ranchers.

 

Know the Quality of Your Forage

 

"Forage testing helps ensure the feed you are feeding your cattle meets their nutritional requirements," says Kevin Sedivec, Extension rangeland management specialist. "This is especially important when grazing cover crops because the quality will vary, depending on the species, varieties and maturity."

 

Forage quality parameters to be most concerned with include crude protein, digestibility, fiber level and minerals.

 

Brassicas such as turnips and radish often are incorporated into cover crop mixes as a high-quality forage. Research on species and variety of brassicas conducted at NDSU found crude proteins of 14% to 27% and total digestible nutrients of 70% to 80%. In addition, brassicas can contain as much as 80% water, depending on the timing of grazing.

 

This combination can disrupt rumen function if high-fiber plants such as millet, sorghum, sudangrass and corn are not included in the mix. Ranchers may need to provide low-quality supplemental fiber, such as low-quality hay or straw, to increase intake and maintain performance.

 

Be Aware of Potential Toxins

 

Many species of cover crops have the potential to be toxic to cattle. Producers must be aware of potentially toxic species, conditions that increase the risk of toxicity and grazing management practices that reduce the potential of cattle consuming toxic forage. The most common toxicities associated with cover crops include hydrocyanic acid (HCN), nitrate and sulfur.

 

Forage sorghum, sudangrass and hybrids contain HCN in the leaves and stems. The concentration of HCN depends on the species, variety, maturity, plant injury and environmental damage (hail and frost). The concentrations of HCN decrease as the plant matures. Damage or injury to the plant from hail, insects, frost or harvest breaks cells and releases the toxins.

 

These grazing management strategies reduce the potential for HCN toxicity:

 

* Delay grazing cattle until forage is 18 to 24 inches tall.

 

* Avoid grazing regrowth under 12 inches.

 

* Do not graze following hail or a light frost. Grazing after a killing frost is safe because the HCN dissipates quickly after the plant dies.

 

Nitrates can accumulate in small-grain forages (wheat, oats, rye, triticale and barley), sorghum, sudangrass and corn. When plants encounter stressful growing conditions, photosynthesis is inhibited and the potential for accumulation of nitrates is increased.

 

"We typically associate nitrate accumulation with drought stress, but it also can accumulate during prolonged periods of cool, cloudy weather," Meehan says.

 

These strategies can help reduce the risk of nitrate poisoning when grazing:

 

* Do not move hungry cows.

 

* Provide cattle with roughage to reduce the amount of nitrate ingested.

 

* Do not overstock pastures when grazing high-nitrate forages. Overstocking increases the amount of high-nitrate plant parts (stems and stalks) that cows consume.

 

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