University of Minnesota Beef Team
For most of the Midwest, the spring and summer of 2010 have been good to us. Most areas have received adequate rainfall to support stellar crop growth, and some areas have received more than adequate rainfall, making it very difficult to get hay put up without rain. Whatever your challenge is, one cannot argue that pastures have been doing extremely well this year.
For those producers who utilize legumes in their pastures - beware. Typically, the first grazing on a mixed pasture (grasses and legumes) will result in a very good balance between the two types of forage. However, most grass species will lose ground, in comparison to the legumes, as the summer progresses. In some cases, pastures can appear to be purely legume stands, which must be managed carefully.
Bloat, or ruminal tympany, is caused by excess gas in the rumen, which cannot be eructated (belched) for any one of multiple reasons. In the case of secondary ruminal tympany, the cause is usually some type of physical obstruction, or physiologic obstruction. Examples of physical obstruction might be choke (foreign body in the esophagus), or positioning of a cow in such a way (low, uneven terrain) that the rumen contents covers the cardia (area where the esophagus enters the rumen), so that the gasses can not be released. Examples of physiologic obstruction would include tetanus, milk fever, vagal indigestion (long-term result of pneumonia), and any other disorder that decreases rumen contractions.
Primary ruminal tympany is caused by the production of a stable froth, which does not allow normal eructation (belching). Primary ruminal tympany is usually classified two ways: Pasture bloat and grain bloat.
Pasture bloat typically occurs in the spring and fall, when legumes are typically immature, and there is likely to be fairly heavy dews on the pastures.
The immature legumes will have a higher percentage of soluble proteins, as well as an increase in moisture content, both of which are significant contributors to the creation of the stable froth that results in pasture bloat.
Typically, as the summer progresses, rainfall decreases, plants become more mature, and the amount of dew present on pastures decreases. This combination of factors leads to a significant decrease in the risk of bloat during the middle to end of summer.
However, in some areas, none of these “typical” events are occurring, and legume pastures in these areas are higher risk now, than they were in the spring. Since bloat is difficult to predict, can be very quick in its development and progression (<4 hrs), and because cattle on pasture can sometimes be difficult to observe, treatment is often an emergency (manual puncture of the rumen behind the last rib on the left side of the animal), if one is lucky enough to find the bloated animal before it becomes a carcass.
Grain bloat most often occurs in dairies and feedlots, where animals are fed high concentrate rations. Particle size is implicated in cases of grain bloat. Smaller, finer particles create a more homogeneous froth, which becomes more stable at a lower pH (rumen acidosis). Animals that are fed legumes in addition to high concentrate rations are at an increased susceptibility for grain bloat.
Providing adequately large particle size will not only decrease the creation of the stable froth, but will also increase the time an animal spends ruminating. Increased rumination will increase saliva production. Saliva acts to buffer the rumen, keeping the pH at a more normal level. Saliva also contains very important proteins and mucin that aid in breaking up the froth, and help prevent bloat.
Some pasture legumes have been selected for a decreased risk for causing bloat. These plant types will have slightly lower soluble proteins, tend to be more fibrous than their normal counterparts, and in general, will take longer to digest.
Water content in and on the plants also contributes to bloat, as the increase in water will increase the volume of froth, and will also decrease saliva production, which will allow increased formation of the froth in the rumen.
Animals also have genetic susceptibility to bloat. Cattle that are more susceptible typically have a larger rumen volume, and often have specific salivary protein concentrations that differ from cattle that are less susceptible to bloat.
As with most herd health issues, prevention of bloat is the best option. In Australia and New Zealand, producers were using oils and tallows to break up the tiny bubbles in the froth. These were either drenched daily, sprayed directly on the pastures to be grazed, or were smeared on the flanks of the cattle, to be licked off over the course of the day. This is an impractical practice in most of the Midwest.
Poloxalene is used to break up the froth in emergency situations (drench), but also is contained in molasses blocks that can be placed in the pasture to be grazed, so that the cattle can consume it as they are grazing the bloat causing forages. There is some data to show that the ionophores (monensin and lasalocid) also aid in the prevention of bloat.
The best prevention is to avoid grazing immature legumes, and wait for the pastures to reach a level of maturity and fiber content that is safe for the cattle to graze.
Bloat can be very hard to predict, and often is dependent upon factors that are beyond our control. Keeping a close eye on your pastures, and reacting to changing conditions will help you stay out of trouble.
For additional information about this or other cattle related topics, please visit the University of Minnesota website at www.extension.umn.edu/beef.