Bloat is defined as the over distention of the rumen and reticulum with the normal gases of fermentation. This can be either if the form of a persistent foam mixed with the rumen contents, called primary or frothy bloat, or in the form of actual free gas separated from the rumen contents, called secondary or free-gas bloat. Bloat is a condition seen commonly in cattle and may also be seen in sheep. Susceptibility to bloat varies by the individual and is genetically determined. Unrelieved bloat is a fatal condition.
Large volumes of carbon dioxide and methane gas are normally produced in the rumen of the cow as a part of its digestive process. This gas must be released by eructation (belching or burping), otherwise the large ever increasing volume and pressure would be incompatible with life. Free gas bloat is secondary to some condition that prevents normal eructation. This may be a result of esophageal obstruction due to a foreign body, (apple, potato or turnip) inflammation around the esophagus (dying grub), stenosis or scar tissue (previous choke from a foreign body) or pressure from enlargement outside the esophagus (enlarged lymph nodes or tumors.) Interference with esophageal function due to nerve impairment may also result in failure of eructation. Free gas bloat may also be a result of rumen atony (lack of normal muscle tone) that may follow anaphylaxis (allergic shock) or grain overload (acute acidosis). Anytime that the rumen stops its normal muscular contractions that mix the ingesta, fermentation continues to occur, and free gas bloat will result. It also can occur due to positional problems. Cattle cast on their side, whether on purpose (anesthesia or positioning for surgery) or by accident (on their side with legs facing up a hill, where they cannot rise) will be unable to belch because the opening to the esophagus will be under water so to speak (beneath the gas/liquid interface) and the gas cannot be eliminated.
Free gas bloat can be treated by passing a large bore stomach tube down the mouth into the rumen, or in cases of positional bloat, getting the cow into an upright position. However, while treating the bloat will relieve the pressure on the rumen, it may not address the underlying problem causing the bloat. A trocar placed into the left paralumbar fossa (flank depression) will also temporarily reduce free gas bloat.
Frothy bloat is considered primary bloat because the production of gas mixed with ingesta (froth) is the cause of the bloat. Frothy bloat is frequently associated with the grazing of bloat producing pastures, but it can also be seen with the feeding of finely ground feed and occasionally seen with the feeding of high quality hay. The rumen is still functional, and continues its contractions, mixing stable gas bubbles into the ruminal contents resulting in a stable foam. The coalescence of the gas bubbles into free gas is inhibited, the foam cannot be eructated, and intraruminal pressure increases. Several factors influence the development of the stable foam. It is believed that certain proteins, saponins and hemicelluloses are the primary foaming agents. Protein content and rate of digestion, including the rate of ruminal passage seem to reflect a particular feeds ability to produce bloat.
Frothy bloat is most commonly seen in animals grazing pure or mostly legume pastures, particularly alfalfa and clovers (ladino, red, white). It can also be seen with grazing young green cereal crops (wheat, rye and oats), rape, kale, turnips and legume vegetable crops (peas and beans). Legumes such as alfalfa and clover tend to have a higher protein content that is highly and rapidly digestible. Other legumes such as sainfoin, crown vetch, milk vetch and birdsfoot trefoil are high in protein, but do not cause bloat, probably because they contain tannins, which precipitate protein and are much more slowly digested than the bloat producing legumes. Alfalfa is one of the few forages that is capable of sustaining levels of production that are comparable to those achieved in the feedlot. Pure alfalfa stands have the potential to more than double the net farm income generated from mixed grass-legume pastures.
Alfalfa has an initial rate of ruminal digestion that is five to ten times greater than that of most grasses. The rapid microbial digestion of alfalfa reduces the particle size of the plant and increases the passage of digested material from the rumen, enabling the animal to consume greater quantities of forage. This rapid digestion and increased consumption is responsible for the high productivity of cattle on alfalfa pasture but it also is at least partially responsible for the incidence of bloat.
Bloat risk with alfalfa, (and all forages with some risk of bloat) is highest when it is in the lush vegetative to early bloom stages of growth. Soluble protein levels may also be higher in the alfalfa plant early in the day, and this may contribute to somewhat reduced bloat risk if cattle are turned out late in the day. As alfalfa enters into the full bloom or post bloom stages, the soluble protein levels decrease, plant cell walls thick, lignin (the woody component of plants) content increases and the rate of digestion drops. Once alfalfa has reached 15-20 percent bloom stage, the risk of bloat drops substantially. As alfalfa entire the full bloom or post bloom stages, the rate of its digestion slows down and the risk of bloat is further reduced.
A killing frost does not in and of itself, reduce the risk of alfalfa bloat. Freezing can rupture plant cell walls and actually increase the release of soluble proteins in the plant. Probably the risk of bloat in frozen alfalfa decreases with time as the proteins form complexes with carbohydrates in a manner similar to that produced by wilting or drying. However, cattle can bloat of high-quality alfalfa hay and long term frozen alfalfa should be considered risk reduced, but not bloat safe. As a general rule, alfalfa is safe to graze 2 weeks after a killing frost.
Experience seems to confirm that cattle must learn to graze alfalfa. Cattle inexperienced with alfalfa will invariably graze other forages preferentially, which can result in a false sense of security as cattle will seldom bloat while these other forages are present in the stand. Once the grasses are depleted, the risk of bloat increases and may be responsible for the phenomena of bloat outbreaks 2-3 days after being introduced to new pasture.
Uniform and regular intake in the key to managing animals on legume pastures. Cattle need to be fed to satiety before being introduced to heavy stands of alfalfa. If rotational grazing is used, care should be given to ensuring that the initial paddock is not over-grazed to the point that the cattle are ravenous when they are introduced to a fresh pasture. High stocking densities increase competition for the alfalfa and reduce the likelihood of any one animal selectively grazing only the lush succulent top potion of the plant. Environmental factors that interrupt regular grazing , such as storms, extreme hot weather or biting flies, can alter intake pattern and increase the risk of bloat. Cattle generally have 3-4 grazing times per day on alfalfa pastures. The 2 major times are right after sunrise and early in the evening. Bloat usually occurs one to one and a half hours after a major grazing period. Being familiar with your cattle’s habits can enable you to observe the animals during times of greatest bloat risk. Once started on heavy alfalfa pasture, every effort should be make to maintain the herd on alfalfa.
Frothy bloat is also seen in feedlot cattle and sometimes dairy cattle on high grain diets. Exact cause of feedlot bloat is unknown, but may be associated with the production of an insoluble slime by certain species of rumen bacteria found in cattle on high- grain rations. It also may be related to the trapping of the gases of fermentation by the fine particle size of ground feed. Very fine particle size of ground feed, in addition to low roughage diets, can markedly affect foam stability, predisposing to frothy bloat.
Bloat is a common cause of sudden death. Cattle that are not observed closely may be found dead. Pasture bloat may develop on the first day on pasture, but may also occur on the second or third day. Affected animals show obvious distention of the rumen, and the left flank becomes so distended that the contour of the paralumber fossa extends above the backbone of the animal. As the bloat continues, the left flank becomes progressively more taut, the skin tightening like a drum (thus also called ruminal tympany). Difficult breathing (including open-mouthed breathing) and grunting are marked, the tongue may protrude, the head may be extended and urination is frequent. Vomiting may occur. The rumen will continue to be motile until bloat is severe. If the bloat continues to worsen, the animal will collapse and die. Death may occur within 1 hour of the development of clinical signs but is more common after 3-4 hours.
Treatment will depend upon the clinical condition of the animals when found. If death is not imminent, a large bore stomach tube may be passed and attempts to find large pockets of coalesced gas may be made. However, in frothy bloat, it may be impossible to relieve any pressure with a stomach tube, and an antifoaming agent should be given through the tube directly into the rumen. If the bloat is not immediately relieved by the antifoaming agent, then close observation of the animal must continue to determine if other life-saving alternative therapies must be given. Tying a rag through the mouth and around the back of the head will cause the animal to chew and produce saliva. This is an old-time treatment that is based in science. Saliva is full of mucin which breaks down the foam of frothy bloat; the amount of mucin in saliva is genetically determined, which helps to explain why some animals are more prone to bloat than others. This method is not recommended in place of other treatments, but if it is all that is available, it could be a life saver.
If the animal’s condition is dire, then a trocar and cannula may be used for emergency relief. A standard trocar is not large enough to adequately release the stable foam. A larger bore instrument, about one inch in diameter must be used. Trocars this large cannot be punched through the skin directly into the rumen: a skin incision must be made first and then the trocar can be placed through the muscle wall into the rumen. If a trocar this large does not relieve the bloat, then an emergency rumenotomy (surgical incision through the skin and muscle layer into the rumen). Antifoaming agents can be administered directly into the rumen through either a cannula or a rumenotomy incision.
There are a variety of antifoaming agents that will be effective. Peanut, corn soybean and mineral oils at a dose of 250-500 mls, sometimes mixed with the surfactant dioctyl sodium sulfosuccinate (docusate) as a proprietary blend, are very useful if given early. Poloxalene (Therabloat) at a dose of 25-50 grams orally or into the rumen is effective for legume bloat, but not for feedlot bloat. Bloat treatments are available from your veterinarian in a premeasured bottle. In an emergency, powdered laundry detergents mixed ½ cup per 16 ounces of water supposedly will work as an antifoaming mixture. In extremely difficult animals, liquid detergent has been squirted on their flanks, so that the animals lick it off of each other and effectively debloat themselves. Again, this could not even be expected to be remotely effective in the moribund animal. Another old technique is to mix 1 tablespoon of kerosene to 6 ounces of mineral oil and use as a drench. In most cases of bloat, drenching is not recommended because the animal is at high risk of aspirating the drench into the lungs. The idea behind mixing kerosene with oil is to impart some flavor to the otherwise tasteless mineral oil and hopefully prevent the animal from aspirating. (The logic being if it can taste the kerosene, it will know to swallow the drench.) All of these treatments rely on the antifoaming properties of the various ingredients. Once the foam is broken down, it will coalesce into large packets of free gas that can be either eructated or removed via stomach tube or trocar.
Prevention of pasture bloat can be difficult and there is no guaranteed preventative tactic. Saliva has natural anti-foaming capability, and anything to increase salivation will decrease bloat potential. Initial introduction to a bloat prone pasture may include a full feed of hay before turning the cattle onto pasture (reducing hunger, increasing saliva content in the rumen and increasing the time for digestion). Turning cattle onto dry pasture is also an important part of bloat prevention. Dry pasture will require more saliva to ingest the feed, so cattle should be given new pasture later during the day when the dew is off and avoid new pasture immediately after a rain. Pasturing more mature stands of legumes will reduce bloat potential, so it is important to avoid grazing pre-bloom pastures.
Feeding antifoaming agents on a daily or twice daily schedule is also a viable preventative measure. Oils and fats given at 60-120 ml per head per day may be effective, although doses up to 240 ml per head may need to be given during the most dangerous periods. Poloxalene is a highly effective surfactant that can be fiven at 10-20 g/head/day and up to 40 g/head/day in high risk situations It is safe and economical and can be given daily by adding to water, grain or molasses blocks (Bloatgard). Alcohol ethoxylate detergents are equally effective and are better tasting than poloxalene, but to my knowledge they are not available in the
Pastures can be sprayed with antifoaming agents such as mineral oil; this is effective if the area is strip grazed, and treated just prior to grazing. This is ideal during strip grazing, but impractical if not impossible when grazing is uncontrolled over large areas.
Perhaps the ultimate aim in prevention is to grow a pasture that permits hugh production while keeping bloat to a minimum. The use of legumes mixed with grasses in equal amount comes closest to this ideal. There are low risk LIRD (low initial rate of digestion) varieties of alfalfa available commercially. Seeding legumes with high condensed tannins in the pasture mix (10% sainfoin) can reduce the risk of bloat with strip grazing.
The grazing of pure alfalfa stands is capable of producing beef at a rate comparable to feedlot growth. It is, however, not without substantial risk. Similarly to the production of cattle in feedlots, pure alfalfa graziers should adopt the concept of what is considered an acceptable death loss.
Preventing Pasture Bloat
1. Plant pastures so that no more than 50 percent of the forage mixture is alfalfa or clover. Consider planting non-bloating legumes. Over seed heavy legume pastures with grass seed.
2. Fill cattle on dry roughage (hay) or grass pastures before turning onto legume pastures.
3. Provide other feed, such as grass pasture, hay, crop residue or grain along with the legume pasture to reduce intake of bloat-producing forage.
4. Strip graze or rotationally graze grass-legume pasture to force cattle to eat most of the plant material, rather than just the succulent top growth.
5. Never move cattle in the morning: is better.
6. Moving cattle in the rain is less risky than moving them 2 days later when it is hot. Under those conditions, alfalfa is growing rapidly and high risk for bloat.
7. Provide constant access to anti-foaming agents such as poloxalene.
8. Once cattle are turned out on pasture, do not remove them at the first sign of rumen distention. Mild, resolving bloat occurs frequently and repeatedly on alfalfa pasture. Animals will not be distressed, and will continue ruminating (chewing their cud.) Moderate bloat may be resolved by simply keeping the animal moving until the bloat dissipates. Cattle with greatly distended rumens should be removed from the pasture and treated immediately.