Q. I need information on frost as related to increased risk of bloat in cattle that graze alfalfa. (June 8, 2012)
A. Alfalfa reacts two ways to a hard freeze. Nitrate levels can increase, but rarely to hazardous levels. Freezing also causes alfalfa to be more likely to cause bloat for a few days after the frost. Then, several days later after plants begin to wilt or grow again; alfalfa becomes less likely to cause bloat. So waiting to graze alfalfa until well after a hard freeze is a good, safe management practice.
Fall grazing of alfalfa is not without problems, though. Bloat always must be a concern, but alfalfa that has been frosted and started to dry down has fewer tendencies to cause bloat than summer alfalfa.
To protect your livestock from bloat, fill them with hay before turning them onto alfalfa. Also, maintain access to dry hay or corn stalks while grazing alfalfa to help reduce bloat.
Finally, bloat protectants like Poloxalene can be fed as blocks or mixed with grain. This can be an expensive supplement, but it works well when animals eat a uniform amount each day.
Also be careful not to damage your alfalfa stand. Only graze when fields are dry and firm. Reserve a small sacrifice area to graze and for feeding when soils are wet to avoid damaging the entire field.
Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln, Lincoln, NE