Every year about now, thousands of head of cattle are turned out on lush, green pastures that have sprung up after a long hard winter. Maybe this description is a bit of an exaggeration but the basics are accurate. As temperatures warm and moisture levels increase in many cases, growth of lush grasses and legumes increases dramatically. This may be especially true this year in areas that have been under severe drought and may now be receiving some rainfall for the first time in months. While the rainfall is a blessing the potential problems may not be.
Endemic with the growth of these pastures is a condition most cattle producers are familiar with to at least some degree, that of bloat. Bloat is often classified as being either pasture or feedlot bloat. It is more accurate to identify it as being either free-gas bloat or frothy bloat. Frothy bloat normally occurs in cattle eating legumes or lush grasses as well as in feedlot cattle. Free-gas bloat is less common on pasture or in the feedlot.
Bloat is a digestive disorder characterized by an accumulation of gas in the first two compartments of a ruminant's stomach (the rumen and reticulum). Production of gas (primarily carbon dioxide and methane) is a normal result of fermentation processes. The gas is usually discharged by belching (eructation) but, if the animal is unable to remove the excess gas, pressure builds up in the rumen-reticulum exerting pressure on the diaphragm which prevents the animal from inhaling, and bloat occurs. The most common type of bloat is frothy bloat where gas builds up in a foam or froth above the rumen contents and the normal belching is inhibited.
Observable bloat can occur after as little as 15 minutes of grazing. Often the animal bloats only mildly and stops eating. The discomfort is eventually relieved. In more severe bloat, the animal's rumen is distended by ballooning of the rumen, it urinates and defecates frequently, bellows and staggers. Death, due to restricted breathing and heart failure follows unless action is taken.
Bloat can occur on any forage that is low in fiber and high in protein but is most common on immature legume pastures. As noted before, frothy bloat results from the production of a stable foam that does not allow gas bubbles to form free gas and be "belched" off. It usually occurs in cattle grazing lush legumes, such as alfalfa, ladino, or white clover. The danger of bloat is greatest when pasture plants are young, lush, and high in soluble protein. The disorder is due to the foaming properties of soluble leaf proteins, which are more prevalent in legumes. The essential feature is that rupture of the naturally occurring small gas bubbles is inhibited and intraruminal pressure increases because eructation (belching) cannot occur. This condition can arise from diets of lush legumes or winter wheat pasture. It may also be seen with high-concentrate finishing ratios in the feedlot. Table 1 categorizes a number of different forages by their tendency to cause bloating in cattle. Current research supports both animal and plant characteristics as having an effect on incidences of bloat. Research has shown that some cattle can be classified according to their susceptibility to pasture bloat into high or low susceptibility and the offspring show influences of their parentage. A number of inherited characteristics are related to bloat. Individual cattle have been classified as having either high or low susceptibility to legume bloat. Highly susceptible cattle typically have larger rumen volumes than “non-bloating” animals. There is a slower rate of passage of particles from the rumen in bloating cows. In one research study, cattle that bloated on a given day consumed 18 to 25 percent less alfalfa immediately before bloat than non-bloaters did in the same time period.
Bloating usually occurs when cattle are first turned onto legume pastures. It seldom occurs on grasses, (or pastures with at least 50 percent grass), coarser pastures, or hay. Bloat usually follows a heavy feeding or grazing period. Animals that are hungry or greedy feeders are most susceptible. This is one reason why, in many cases, a producer will see his “best-doing” cattle are the ones which can develop this condition, due largely to their aggressive eating habits. Other conditions also increase the incidence such as frost, dew or rain on the field. Bloat incidence is likely to be increased during periods of rapid plant growth in the spring or following a summer rain. Also, adaptation of animals to a particular feed is an important factor. Animals may be at increased susceptibility for the short-term due to changes in rumen microflora. As animals become adjusted to a particular pasture or ration, they have less susceptibility to bloat. Cattle that are unadapted to the fresh forage tend to be the most susceptible, i.e. fresh stocker cattle just turned out for gain.
An old wive's tale stating that the risk of bloat may be reduced by waiting until the dew is off the alfalfa is true. A study demonstrated that cattle were 2 to 17 times more often likely to bloat when fed between 7 and 8 a.m. than when they were fed 4 hours later.
All this being said, most bloat occurs:
• When cattle are first turned onto pastures in the spring.
• When cattle are moved to new pastures if the previous pasture was grazed too short so that cattle are hungry.
• In late summer, during periods of rapid plant growth after rain following a period of drought.
Reducing the Incidence of Bloat
Sound management can help reduce the incidence of bloat. It probably will not eliminate it completely but it can reduce it substantially. Some steps to take can include:
1. Begin grazing in the spring on pastures that are grass or grass-legume (at least 50 percent grass) mixtures. This will allow the animal time to adjust to the pasture.
2. Make sure that the animal is full when first put onto pasture in the spring. This reduces the intake of the fresh pasture until the rumen has had time to adjust to the new feedstuff.
3. Do not start animals grazing when the forage is wet from dew or rain.
4. Start animals on legume pastures gradually. For example, leave cattle on pasture one hour the first day and gradually increase grazing time to four hours by the third day and day-long grazing by day five.
5. Be sure that fiber is maintained in the animal ration during initial grazing periods. Feed some dry hay or corn silage to grazing animals prior to turning them out to pasture.
6. Check animals for bloat carefully every two hours when beginning grazing.
7. When rotating cattle or sheep among pastures, be sure that animals are moved fast enough so that they are not excessively hungry when going onto fresh pastures.
8. Animals with supplemental feed will be less likely to bloat. For example, a dairy cow, where 40 to 50 percent of the intake is pasture will be less likely to bloat than beef cattle, dairy heifers, and sheep, where pasture comprises 100 percent of the diet. Stocker cattle receiving at least a couple of pounds of supplement are also less susceptible.
9. Where bloat has been a problem, consider seeding using birdsfoot trefoil as the legume because it is non-bloating.
10. Consider using Bloat Guard® (Poloxalene) during periods where bloat is likely. Poloxolene can be mixed with grain supplement or drinking water, drenched, or fed as a pasture block. Effectiveness of this product depends on daily intake. Thus mixing with a daily supplement is more effective than feeding in blocks on pasture. Another useful product is Rumensin® which has also shown efficacy in reducing the incidence of bloating
11. Some animals are chronic bloaters. If a particular animal frequently shows signs of bloat, it may be best to remove that animal from the herd.
What if a Case of Bloat Develops?
Inevitably, no matter how hard you try and how well you manage, you will still, from time to time, encounter some problems with bloating. When bloat is observed, immediately remove all animals from pasture and offer dry hay. This will reduce the bloat problem in all animals that will eat. Forcing bloated animals to walk is also helpful. Bloat
can cause death in as little as 1 hour so it is important to be prepared to render emergency treatment. When handling an effected animal remember to move them calmly and quietly. As noted, the walking may improve the physical conditions in the rumen causing the animal to eructate, thus releasing some of the gas. If the bloating has not been lessened once you get the animal to the pen then several options are possible. They include:
1) stomach tubing – this involves restraining the animal and passing a rubber hose down it's esophagus (taking care to avoid passing it into the animal's trachea) and into the rumen providing a mechanical release of the gas.
2) Administration of oil – using a vegetable oil drench will reduce the surface tension and allow the gas to escape.
3) Trocar – This should be the last possible consideration and only in the case of a true emergency. Use of a trocar, a devise that punctures the rumen from the outside is a rapid and effective means of releasing the gas. It also provides a tremendous opportunity for introduction of infection.
As with many conditions, the best defense is a good offense. It is much more effective to take a proactive stance in the prevention of bloat than have to treat it after it occurs. In most cases this involves planned avoidance understanding that some isolated incidences may very well occur. Once again, good management is crucial to prevention.
Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.