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Unseasonably warm temperatures have brought about an early spring flush of legumes in our pastures. As a result, the UK Veterinary Diagnostic Lab is already examining cases of frothy bloat in beef cattle.
Bloat is caused by an abnormal collection of gas in the rumen. Bloat results when an animal cannot “belch up” gases produced in the process of rumen fermentation. Pasture bloat usually occurs in cattle grazing lush legumes, such as alfalfa and ladino clover. There have been reports cattle grazing in red clover, but the risk of bloat is much lower than ladino clover. Small grains and ryegrass also have the potential to cause bloat.
The danger of pasture (frothy) bloat is greatest when pasture plants are young, lush, and high in soluble protein. Frothy bloat results from the production of a stable foam that does not allow gas bubbles to form free gas and be “belched” off. The disorder is due to the foaming properties of soluble leaf proteins, which are more prevalent in legumes.
A cow’s inability to expel the gas allows pressure to build up in the rumen. As the pressure increases, the rumen becomes distended on the cow’s upper left side between the last rib and the point of the hip. As the bloat becomes more severe, breathing becomes difficult. After the cow is no longer able to stand, death follows within a few minutes.
In these severe cases, a ¾-inch to 1-inch rubber hose can be passed through the throat (with the use of a metal tube/speculum to prevent chewing the tube) into the rumen to provide relief. Since pasture bloat is frothy, a tube to the rumen may not be sufficient. If it is not adequate, a defoaming agent (oral bloat medicine, vegetable oil, or dish detergent) may be added through the tube.
As a last resort, relief can be obtained by making a surgical hole in the rumen large enough to release the foam. An incision is made on the left side at a point halfway between the last rib and the hook bone. The incision must be sutured, and antibiotics must be administered.
The best plan is to prevent bloat. The most common antifoaming surfactant and the only one currently approved for use in the United States is poloxalene, which is incorporated into a small block (i.e., 33.3 lb) form. Most blocks are labeled to be fed at a rate of one block to every five head of grazing cattle. To encourage intake of bloat blocks, other sources of salt and salt containing mineral supplements should be removed from pastures when using them.
Bloat preventing products, such as Bloatguard®, are effective if consumed daily in adequate amounts. Rumensin® (monensin) has been demonstrated to reduce a large percentage of bloats.
When cattle graze lush plants capable of causing legume bloat, no management practices will ensure bloat doesn’t occur. The following management strategies can, however, reduce its incidence:
• Grow grass-legume mixtures instead of pure legumes.
• Avoid grazing very immature white clover or alfalfa. Research shows alfalfa grazed less than 10 inches tall had two times more bloat than when it is grazed at 19 inches.
• Put animals on lush legume pastures only when plants are free of surface moisture (dew or rain).
• Provide a full feeding of hay before turning animals into lush legume stands for the first time.
• Although bloat is associated with certain plants, some animals have a genetic predisposition to bloat, so you should cull chronic bloaters.
• Do not remove animals from pasture during first signs of bloat. Continuous grazing results in less incidence of bloat than removal and return.
• Provide access to water and minerals.
• Observe animals closely following any abrupt change in the weather.
• Feed bloat-reducing compounds.
For more information ask for UK Extension publication ID-186: Managing Legume-Induced Bloat in Cattle or ID-108: The Kentucky Beef Book.
Michael Pyles is Trimble County’s Cooperative Extension agent for agriculture.