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Using Alfalfa and Grass Hayfields after Frost

26 October 2012
Ohio State University

US - We have had some frost over the past couple of weeks and one question that comes up is the use of alfalfa and/or grass hayfields following a frost. Management after a frost depends upon several factors. Was there a frost or a killing freeze? Is the hayfield a legume or a grass stand? What are the needs and goals of the hayfield's owner, asks Rory Lewandowski, University of Ohio.

Temperature is a consideration. A frost may burn the top of the plant, but growth will still continue from the green, unburned leaf area. A killing freeze for alfalfa is generally defined as a temperature in the 24 to 25 degree F range over a period of at least 4 hours. After a killing freeze, alfalfa is done growing and the plant can be cut for mechanical harvest, grazed, or left to overwinter. Due to this year's drought, most livestock owners need to use whatever forage is available, and I expect to see fields harvested or grazed following a killing freeze.

Sometimes the question is asked if too much top growth can lead to smothering over the winter. In alfalfa this is not an issue because the leaves will dry up following a killing freeze, become brittle and drop off the plant. The stem that remains standing is not a concern for smothering the stand. Tall grass plants however can mat down. This mat can provide a habitat favorable for disease development that could thin out the stand. For this reason, it is recommended that a grass hay field with tall growth be cut or grazed before winter.

With our shorter days and cooler temperatures it becomes very difficult to get a cut legume or grass to dry down enough to bale as a dry forage. Wrapping wilted forage or harvesting as baleage is the best mechanical option. Grazing a hayfield is usually a more economical option as compared to mechanical harvest. Use of temporary electric fencing can facilitate the grazing use of a hayfield. While forages such as alfalfa, clovers and cool-season perennial grasses do not produce toxic compounds after a frost, bloat can be a concern when alfalfa or clovers are grazed after a frost.

The risk of bloat is higher one to two days after a killing frost and when livestock are grazing a pure or mostly pure legume stand. The safest management practice is to wait a few days after a killing frost before grazing pure legume stands. At that point the forage will begin to dry from the frost damage. If animals are not accustomed to grazing high legume content stands, it is a good idea to feed some dry hay before turning into the legume field, or move animals into the legume field in the late morning or early afternoon after they have been grazing another pasture so that they are not entering with an empty rumen.

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