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Frost, Alfalfa and Bloat

By Jenifer Heyden, M.Sc., PAg, Regional Livestock Specialist, North Battleford

September 2018

Do you have alfalfa or clover regrowth that you’re planning on grazing this fall? Are you worried about bloat? Should you be worried about bloat? With recent frosts and a decline in available pasture, many producers have been inquiring about turning their cows out onto alfalfa regrowth.

Legumes such as alfalfa and clover can cause bloat in cattle. Non-bloat legumes include species such as birds foot trefoil, sainfoin and cicer milk vetch. Bloat causing forages are digested rapidly whereas bloat safe forages are digested more slowly.

Alfalfa and clover can cause frothy bloat if not managed properly. Frothy bloat results from the quick degradation and fermentation of plant material and rapid release of plant cell contents. Gases are trapped in a thick foam in the rumen and the cattle are not able to burp to release the gas.

The first killing frost also plays an important role in bloat. Frost preserves the stage of growth at which the alfalfa is at, at that point in time. Second growth may be immature, and immature plants are the more likely to cause bloat. With a killing frost, the frost disrupts the plant cells and increases the rate of cell breakdown. The plants must then dehydrate or desiccate in order to become safe for consumption.

The plant cells in a lush, young alfalfa plant are very turgid, like a recently blown up balloon. A balloon that you’ve just blown up is easy to pop, thus releasing plant cell contents rapidly. As alfalfa matures and the number of frost events increases, the risk of bloat declines. The plants begin to wilt and the plant cell balloons begin to deflate, so to speak, and it takes more time for degradation to occur, thus reducing the risk of bloat.

For producers who are concerned about bloat here are some considerations:

  • If possible, offer another source of dry forage along with the alfalfa.
  • Don’t turn out hungry cows. Allow the cattle to consume their normal feed in the morning and introduce them to the alfalfa in the afternoon.
  • Introduce the alfalfa slowly, to allow sufficient time for rumen microbes to adapt to the change in feed.
  • Consider minimizing the area cattle have to graze – this will ensure that cattle are not only selecting the leaves and fines but will force them to clean up the more fibrous stems as well. The more fiber, the less chance of bloat.

If you need more information on grazing alfalfa and managing bloat, contact your local Regional Livestock & Feed Extension Specialist or the Agriculture Knowledge Centre at 1-866-457-2377.

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