While row-crop farmers expect cover crops to serve as a long-term payback from a short-term cost, livestock producers who graze cover crops see a more immediate return on investment. Planting cover crops produces high-quality forage and extends the grazing season into the winter, while also allowing pastures time to recover. The practice nourishes both cattle and the land with one crop.
Along with the benefits, however, there are some special considerations when using cover crops for grazing. As with any forage you feed, it’s important to know the quality to ensure you are meeting the herd’s nutritional requirements. This is particularly true when grazing cover crops. The quality will vary depending on the species, varieties and maturity. Forage quality parameters of most concern include crude protein, digestibility and fiber level as well as minerals.
Brassicas such as turnips and radishes often are incorporated into cover-crop mixes as a high-quality forage. They will have reported crude proteins of 14% to 27%, total digestible nutrients (TDN) of 70% to 80% and a lot of water—80% moisture is not uncommon. This combination can disrupt rumen function if you are not including higher-fiber forages such as grass hays, millet, sorghum or sudangrass. You may need to feed lower-quality hay, straw or other supplemental fiber to increase intake and maintain performance.
Some cover-crop species are potentially toxic to cattle. Be aware of these species, the conditions that increase the risk, and grazing management practices that reduce the potential of cattle consuming toxic forage. The most common toxicities associated with cover crops are hydrocyanic acid (HCN), commonly known as prussic acid, and nitrates.
Sorghum, sudangrass and hybrids contain HCN in the leaves and stems. The concentration depends on the species, variety, maturity, plant injury or damage. 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:
1. Delay grazing cattle until forage is 18 to 24 inches tall.
2. Avoid grazing regrowth under 12 inches.
3. Do not graze following hail or a light frost. Grazing 10 days after a killing frost is safe because the HCN dissipates quickly after the plant dies. When the plants are “lunch bag” brown, they are safe to graze.
Nitrates can accumulate in small-grain forages such as wheat, oats, rye, triticale and barley, or warm-season grasses such as sorghum, sudangrass and corn. Stressful growing conditions inhibit photosynthesis and increase the potential for nitrate accumulation. We typically associate nitrate accumulation with drought stress, but it also can occur during prolonged periods of cool, cloudy weather. This is more likely in wetter, colder areas.
To reduce the risk of nitrate poisoning, provide cattle with a feed concentrate. This adds energy to the diet and dilutes the amount of nitrates eaten. Do not crowd animals. High animal density increases the amount of plant stalks consumed. Nitrates accumulate in the lower plant stem. The picked-over forage in the bunk will have more stems, and thus more nitrates, than average.
A common complaint of 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 limit access is with temporary fencing. Fences can be set up prior to grazing or moving cattle into the next cell.
As you establish your grazing cells, be sure to consider access to water. This may limit the design of your grazing system, because many fields do not have developed water sources. An effective plan is to start grazing in the cell nearest the water source, and then move away from the water, allowing cattle to come back across the grazed areas to drink.
For more advice on growing, grazing and managing cover crops, talk with the livestock and agronomy experts at your MFA or AGChoice location.
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