Eye on Extension: Grazing alfalfa in the fall can be a challenge


VALLEY — In the fall cattle producers often look for feed sources to help put weight on their cows before winter. One option is the grazing of alfalfa fields that have some regrowth. However, the grazing of alfalfa has some risks after a hard freeze.

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, safer management practice.

So what is bloat? Bloat is a buildup of gas in the digestive system, commonly the rumen of ruminant animals. As with most animals this gas is lost thru eructation (belching). Sometimes there is an interruption and the gas builds up faster than it is lost. 

This trapped gas may form a foam or froth in the rumen that further prevents it from being expelled. With the frothy bloat it is harder for animals to expel the gas.  There is also a non-frothy bloat called dry bloat. It is less common. Frothy bloat often occurs on pasture where non-frothy bloat occurs mostly in feedlot conditions.

Bloat can be caused by a number of situations:

• Certain proteins in forages

• Amount, rate of intake and coarseness of the roughage

• Rate of digestion of grains due to fine processing

• Host parasite reaction after grub treatments

• Enlargement of the lymph nodes

• Bloat can be inherited

Preventing bloat is desirable, not only to reduce death but to improve performance.  Pasture (frothy) bloat can occur in animals grazing lush legumes, such as alfalfa or clover, or from grasses such as wheat pasture.

Fall grazing of alfalfa can cause bloat. Alfalfa that has been frosted and started to dry down has fewer tendencies to cause bloat than summer alfalfa. But, turning in to graze too early can increase the risk.

To protect your livestock from bloat, fill them with hay before turning them onto alfalfa. Also, maintain access to dry hay while grazing alfalfa to help reduce bloat.  Bloat protectants 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. Start feeding the bloat guard supplements several days before turning on to an alfalfa pasture. This lets the animals build up a quantity of control before the onset of bloat may occur. 

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.

Cooler temperatures, especially at night, are often associated with bloat.  This may be due to animals eating more in cool weather. Animals also tend to bloat more frequently in the morning, possibly because their biggest meal of the day occurs at this time.

When you change an animals diet, do so slowly. Allow the digestive microbes a chance to get used to the new feed. You may turn animals out for a couple hours then take then off the field for the first couple days.  Then increase the amount of time in the alfalfa field over the next few days until they are there full time.

For more information on this and other topics of interest to you, contact the San Luis Valley Extension Office at 719-852-7381 or email Marvin Reynolds at [email protected]    

Extension programs are available to all without discrimination, Colorado State University Extension, U.S. Department of Agriculture and Colorado counties cooperating.

By Marvin Reynolds is the Area Extension Director for the San Luis Valley Area.

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