Five Tips for Spring Cover Crop Grazing

Keep these tips in mind to maximize the transition to grazing cover crops.

by Denise Schwab, Iowa State University

As fields start to green up from last fall’s cover crops, cattle producers can’t wait to get cows out of calving yards and onto fresh grass. Here are a few tips to remember when grazing cover crops.

1. 1. How long do you want the forage to last? If you want to terminate in a short time, graze as soon as it greens up. If you want some substantial grazing to occur, wait till the forage is about 6 inches tall to start grazing. Typically, cereal rye will be the first forage to break dormancy, followed a week or two later by triticale and wheat. Giving the forage time to get established results in more season-long growth, but graze early enough to prevent it from getting ahead of the cows and getting too mature.
2. 2. Transition the diet. Nothing is worse on the rumen than an abrupt change from a dry forage and grain diet to a wet, high-protein forage-only diet. The rumen microbes need time to adjust to diet changes. Spring cover crops are both high in protein (13%-19% crude protein) and high in water content, resulting in a fast passage rate. The energy content tends to be fairly high (55%-60% total digestible nutrients), but because of the high water content, it is a challenge for the cow to meet her energy and dry-matter intake needs. Continue to supplement your dry forage diet while the cows are grazing cover crops, just cut back on the quantity fed, or provide free-choice dry hay as a supplement. However, supplementing other feed in many cases is not practical since cows generally are not very interested in stored feed once they are turned onto cover crops. The best compromise may be to fill up the cows on their existing ration before turning them out for the first time this spring and allow their gut fill to regulate how much they consume initially.
3. 3. Have a sacrifice paddock or drylot option in case of heavy spring rainfall. Typical spring grazing should not negatively affect grain yields. In some cases it could actually increase yields. However, excessive hoof traffic during extremely wet weather may cause some compaction. It may also cause the need to smooth the soil surface or perform mild tillage to address some surface compaction that may exist. Move water and mineral sites regularly to reduce congregation areas. Consider strip-grazing to both increase forage utilization and to reduce the risk of compaction when raining. When heavy rain or a long stretch of rain occurs, move cows off the field.
4. 4. Beware of grass tetany and nitrate risk. Grass tetany is a risk any time cows are grazing lush spring forages that are high in protein, moisture and potassium, and low in magnesium, calcium and sodium. Feed a high-magnesium mineral for a week or two prior to turnout to reduce the risk of grass tetany. Supplementing dry forage, if cows will eat it, can help to both slow the rate of passage through the digestive system and dilute the low-mineral grass with higher-mineral dry forage. Grasses, including cover crops, are good at scavenging nitrogen from the soil to produce leaf tissue and grain. Cover crops heavily fertilized, manured or following a drought may accumulate nitrates, which can be toxic in the cow. Because nitrates tend to concentrate in the lower part of the plant, use rotational grazing to leave more residue, along with supplemental dry forages to reduce the risk of nitrate toxicity.
5. 5. Termination of the cover crop. Remember that the cover crop needs to have green growing leaf tissue for contact herbicides to work. Plan for 1-2 weeks of regrowth after grazing for herbicide application to be effective.

Keeping these few tips in mind will help make grazing cover crops a positive investment for your cattle operation.

Editor’s note: This article is reprinted with permission from the Growing Beef newsletter. Denise Schwab is an ISU extension beef specialist.

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