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 Pasture & Range: October 1998 Other Pasture & Range Articles |
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by Charles Griffith |
Bloat can be a problem in cattle grazing high quality grasses and legumes. Bloat problems will vary with species of animals and among individuals of the same species. Sheep and goats can be affected by bloat but are considered less susceptible. Bloat is caused by the formation of a stable froth in the rumen of susceptible animals, preventing the normal belching of rumen gasses. The resulting accumulation of excess gas in the rumen produces pressure on the lungs and can eventually restrict breathing to the point of causing death by suffocation.
Bloat is characterized by a gradual swelling of the left side of the animal. Bloat is apparent within 20 minutes to an hour after the onset of gas retention. If the condition is mild, normal movement of the animal will again allow the normal release of excess gas and the condition diminishes. If the gas buildup continues, the animal will collapse and die from suffocation within a relative short time. Immediate treatment is necessary.
Stocker cattle grazing winter pasture during the 1997-98 growing season had abnormal bloat problems. We can only speculate as to the reason why. The summer and fall in most areas were dry and hot. This created conditions for nitrate nitrogen to remain in the soil from the previous growing season and then additional nitrogen was applied prior to fall planting without knowledge of nitrogen levels in the soil. When rain finally came in late October during ideal temperatures, plant growth was very rapid creating an abundance of forage. The winter was mild with good moisture and we experienced excellent plant growth throughout and a likelihood of plants with very high levels of crude protein (CP). Scientists advise that bloat correlates to a group of soluble proteins and at least some of those proteins are enzymes involved in photosynthesis.
Cattle were turned in to graze in late November and early December. As plants were bitten off, regrowth was rapid. The regrowth could have been the problem. Bloat often occurs when cattle graze the lush regrowth of wheat and other winter annual grasses. With excess soil nitrogen these plants will often test in excess of 30% CP.
Plants testing high in CP are not the only cause of bloat, but from our years of experience we know they act as a catalyst that increases the potential for bloat. We have experienced this same situation with cattle grazing legumes such as alfalfa. If cattle graze juvenile plants that test high in CP then the bloat potential is very high. I should add that this does not mean all plants testing high in CP will cause bloat. Also, there are other kinds of bloat, such as feedlot bloat, not associated directly with plants. When cattle graze older plants in the bud to early bloom stage of maturity, bloat is seldom a problem.
From our years of experience we have developed the following guidelines for the management of bloat:- • Test the forage for crude protein or nitrate levels before turning cattle in to graze. Collect the sample in early morning (8 to 10 a.m.) when most bloat problems occur. If the test indicates protein in excess of 20 percent, treat this as a warning of potential bloat problems.
• Set up a multiple pasture rotation grazing system such that you can control when and how intense animals graze a plant and then have the option of removing animals to another pasture so plants can have a designated rest period. Avoid grazing young immature plants. In our experience, cattle grazing "aged" winter pastures in a rotational grazing program seldom have a serious bloat problem.
• Feed some hay before turning animals onto pastures with a high potential for bloat. Then watch animals carefully for an hour or two. If swelling and bloat begin to develop, remove the animals from the pasture quickly. If one animal swells, then treat him as being a highly susceptible animal.
• When using rotational grazing, make pastures small enough or use strip grazing so that animals consume a mixture of stems and leaves and dilute the CP intake.
• When using rotational grazing, plan to make moves in mid-afternoon to minimize grazing of forage with heavy dew, which also correlates to bloat potential and nitrate toxicity.