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. Here are four things for producers to keep in mind as they prepare to graze cover crops this fall.

Know the Quality of Your Forage

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“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.

Know Your Carrying Capacity

The stocking rate is going to depend on the carry capacity of the cover crop and individual management goals. A number of factors influence carrying capacity, including soils, type of cover crop, stage of growth and rainfall. To determine carrying capacity accurately, producers first must determine forage production of the area to be grazed.

The most accurate method to calculate forage production is the clip-and-weigh method, Sedivec says. This method requires the actual harvesting of standing forage at a given time to predict available forage.

The available forage is measured by hand clipping and weighing a specified number of plots within a grazing/forage production area. See NDSU Extension publication “NDSU Range and Forage Production Sample Kits” (https://tinyurl.com/NDSU-RangeSampleKits) for detailed instructions on calculating forage production.

Once forage production has been determined, then make an adjustment for harvest efficiency. Harvest efficiency is the amount of the plant that livestock will impact during the time they are grazing the pasture. Harvest efficiency is expressed as a percent and should be multiplied by the total amount of forage on the pasture to provide the amount of forage available for grazing animals.

When grazing cover crops, harvest efficiency will depend on the desired amount of residue following grazing. The two most common scenarios are take all, no residue left behind, 75% harvest efficiency; and take half, leave half, 35% harvest efficiency.

Design Considerations to Optimize Grazing Efficiency

One common complaint from those grazing cover crops is forage waste. Forage waste can be reduced and harvest efficiency increased by dividing the field into cells based on stocking rate.

Limiting the area cattle can access reduces feed waste and improves nutrient distribution. The most effective way to do this is with temporary fencing. Fences can be set up prior to grazing or prior to moving cattle into the next cell.

When establishing grazing cells, be sure to consider access to water. This may limit the design of the grazing system because many fields do not have developed water sources. The most effective design is to start grazing in the cell nearest the water sources and work away from them, allowing cattle to come back across the grazed cells to access water.

“Integrating cover crops into your grazing system has the potential to enhance cattle and crop production when done properly,” Meehan says. “Keep these keys in mind as you begin grazing cover crops this fall.”