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Preventing bloat in grazing cattle

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By Rick Greenwell

We have had a lot of people to contact us regarding cattle dying and bloat.  Here is an article from Dr. Jeff Lehmkuhler, Dr. Roy Burris, Dr. Michelle Bilderback and Dr. Ray Smith, all University of Kentucky College of Agriculture Specialists.

Bloat has been reported by county extension agents to be a problem this spring with cattle grazing lush pastures.  Good growing conditions for white clover have resulted in pastures containing large amounts of clover and limited precipitation has slowed grass growth.  Cattle are consuming greater quantities of clover due to the short grass resulting in conditions promoting legume bloat or frothy bloat.  Similar conditions can also occur when grazing wheat.

Prevention of frothy bloat is best accomplished by planning in advance.  In a series of articles celebrating the centennial of the American Society of Animal Sciences which were published in the Journal of Animal Sciences in 2008, Vasconcelos and Galyean discussed progression of our understanding of digestive disorders including bloat.  The following information regarding the prevention of legume bloat is based on the published research regarding this topic covered by the authors above as well as product details from the manufacturer.

Unlike gaseous bloat commonly associated with high grain diets, frothy bloat is more difficult to relieve using the esophageal tube approach.  Frothy bloat associated with grazing is often the result of consuming forages that are high in soluble protein combined with rapid fermentation.  This produces a stable foam in the rumen blocking the normal escape of the gas from fermentation through eructation or belching.  This build up of gas results in rumen distension similar to blowing up a balloon which can impact the animal’s ability to breath normally due to pressure against the diaphragm.

This stable foam must be disrupted to allow the gas to escape.  Saliva contains mucin which has been shown to be key in disrupting and preventing the formation of this stable foam.  Wet, lush forages however, reduce chewing activity and saliva production.  Risk is greater during periods when the forage is wet such as when dew is present in the morning and evenings.  Stimulating rumination by providing palatable, good quality grass hay is believed to help prevent frothy bloat.  Some researchers, however, have not shown this to be effective means of preventing or reducing the severity of bloat.

Feed additives are commonly utilized to prevent and reduce the severity of bloat.  Using ionophores hasbeen shown to be effective in preventing and reducing the severity of bloat.  Monensin (Rumensin ™)is commonly utilized in wheat grazing areas to prevent wheat pasture bloat.  It has been shown to be reduce the incidence of frothy bloat from legumes in cattle when consumed at levels near 150-200 milligrams per head daily.  Monensinis readily accessible from feed dealers and several offer mineral products containing it.  It is important to note that free choice mineral mixtures are approved for grazing stockers and replacement heifers.  There is not, however, an approval for providing a free-choice mineral containing monensin for beef cows and it must be mixed in with at least 1 lb of grain supplement according to the product label.

Poloxalene is another feed additive shown to be very effective in preventing frothybloat.  It is more effective than monensin and other ionophores, however, it can be costly to feed.  Poloxalene blocks are commonly utilized by producers for their convenience.  Poloxalene can also be obtained in a powder form to be mixed in supplements or mineral mixtures.  During periods of severe bloat risk, the target intake level of poloxalene is 2 grams per 100 lbs of body weight.  This can be reduced to 1 gram per 100 lbs of bodyweight as the risk to bloat diminishes.  It is recommended that poloxalene be introduced 2-3 days prior to introduction into pastures that are at risk to promote bloat.  Poloxalene must also be consumed on a daily basis as there is no carry over protection.

There are additional practical management strategies to reduce the incidence of frothy bloat.  Ideally, the legume content should be kept below 50% to reduce the risk of bloat throughout the grazing season.  Allowing the legumes to mature to late bud, early bloom stage will also reduce the risk bloat.  Risk to bloat from legumes is reported to be higher for vegetative, prebud stages.  Moving cattle to pastures with less legume content and returning to pastures when the legumes have advanced in maturity might be an effective strategy if such diversity exists on your farm.  Avoid moving cattle to new fields with high legume content when they are hungry.  Attempt to fulfill their hunger with high quality hay if necessary before moving into legume pastures.  Monitor cattle frequently throughout the day.

When faced with an emergency case of frothy bloat, prompt treatment is extremely important as death can occur in as little as one hour after grazing begins but is more commonly seen 3-4 hours after bloat starts. If life threatening, your veterinarian may do an emergency rumenotomy (cutting a hole in the rumen) to relieve the pressure.  If not in immediate danger, passing a stomach tube into the rumen and administering an antifoaming agent such as mineral oil may aid with the problem.  For more information you are encouraged to contact your county Agricultural Extension agent and your veterinarian.