TREATING & THWARTING: Bloat in Cattle: A livestock expert ruminates on the rumen's role in keeping cows healthy.
So what exactly causes bloat, and how can it be treated? Even more importantly, how can it be prevented? When discussing bloat, it helps to know a bit about the rumen, and how the entire ruminant digestive system functions.
We've all heard that cows have four stomachs. This isn't true; they only have one stomach. But it's true that their ruminant digestive system is a complex, multichambered system. Part of this complexity is the precise balance of the microbes that's necessary for the system to function properly.
The RUMEN is the largest part of the digestive system. This large compartment can contain up to 50 gallons of digested feed in large cattle. Smaller cattle will have a proportionally reduced capacity. Regardless of the size of the animal, the rumen still makes up a significant part of the digestive system.
The rumen doesn't perform any specific digestive function, or secrete any digestive enzymes. Instead, the work of digestion is performed by the bacteria that live in the rumen. The rumen can contain up to 50 billion microbes per milliliter of rumen fluid. Even in an organ with such a huge capacity, the sheer number of microbes is staggering.
These microbes are working strenuously to break down the contents of the rumen and convert them into volatile fatty acids (VFAs). The microbes break down and ferment fiber, starch, sugar, and proteins. Once broken down, these materials are converted into VFAs, which are absorbed by the rumen wall. Along the surface of the rumen wall are thousands of papillae (small, finger-like projections of tissue), which help to absorb the nutrients from the VFAs. The cow obtains high-quality nutrition from the VFAs being absorbed by the rumen wall, even though the VFAs are the waste product of the microbes.
The RETICULUM, often called the "honeycomb" because of the likeness of the structure of its tissues, has a capacity of 5 gallons in a mature cow. The rumen and reticulum are regarded as one organ--referred to as the reticulorumen--because they perform similar functions. The reticulum, which catches all heavy items the cow ingests, such as feed and metal objects, is separated from the rumen by a small fold of tissue. Unfortunately, the reticulum lies close to the heart, so those metal objects can work their way into the heart tissue and cause hardware disease--another life-threatening condition.
The OMASUM, which holds up to 15 gallons in a mature cow, serves to absorb water from the digestive tract. The digestive material found here is therefore much drier than the rest of the system.
Lastly, the ABOMASUM, or "true stomach," holds up to 7 gallons. It's the compartment most similar to a human stomach, and it secretes true digestive enzymes to further break down food.
Because they have a ruminant digestive system, cows thrive on coarse, long-stemmed forage. Grass, hay, pasture, and some legumes are the perfect material for the rumen to work on.
Rumination naturally produces a considerable volume of gas, mostly carbon dioxide and methane. Once produced, these gasses rise and reside at the top of the rumen, above the solid and liquid contents. Beneath the gas, there's a "mat" of chewed, long-stemmed fiber which rests on top of the rumen fluid. At the bottom of this fluid is the more digested material, ready to pass out into the rest of the digestive system. As the gas at the top builds up, pressure receptors in the rumen stimulate the sphincter muscles in the esophagus to relax. Gas enters and is released out of the mouth, a process called eructation.
Rumen contractions serve to mix the contents so the microbes are able to make contact with the feed and reach the rumen wall for absorption. Contractions also enable the cow to regurgitate the less digested food and chew it again, helping to break it down further. This is what's known colloquially as "chewing their cud."
The rumen is naturally an anaerobic (without air) environment. The microbes that live and work in the rumen depend on this type of environment to live, and can only tolerate a small amount of oxygen--and only if the rumen is functioning well.
The rumen can function at a pH ranging from 5.7 to 7.3, but a pH level much lower than 6.0 can cause the rumen to become too acidic. The microbes that are responsible for digesting fiber are acid intolerant, and die off quickly at the lower pH levels. The acid that's produced in the rumen when food is broken down is either absorbed by the rumen wall or neutralized by salivary buffers. When there's an increased level of acid in the rumen, the saliva is unable to stabilize the pH level in the rumen. A cow can produce between 12 and 20 gallons of saliva per day, depending on what it's eating. Normally, saliva keeps the rumen pH in the range of 6.2 to 6.8, which ensures efficient digestion of food. The more long-stemmed forage the cow has to chew, the more saliva it produces. The more saliva produced, the more easily the rumen is buffered. And long-stemmed forage also has what's referred to as a "scratch" factor, which stimulates rumen activity and keeps things working as they should.
Diets that are high in concentrates, such as finely ground grains or highly digestible forages, cause the rumen buffering system to become overwhelmed, which can lead to serious problems.
A Sizeable Stomach
Bloat occurs when the systems in place to help eliminate rumen gasses become overwhelmed. There are generally considered to be two types of bloat: frothy and free gas.
FROTHY BLOAT is caused when gasses are trapped in a persistent foam that's not easily released. When this foam builds up over time, the rumen expands and causes bloat. Frothy bloat is also often referred to as "pasture bloat" or "feedlot bloat." It's called this because it occurs most often in cows put on pasture (pasture bloat) and in cows that are fed high levels of finely ground grain (feedlot bloat). Cows in both of these settings consume feed that's rapidly digested in the rumen, which causes a large amount of fine particles that trap gas bubbles. Also, the soluble proteins consumed by cows on pasture, and the bacteria present in animals on feedlots, produce foam in the rumen.
FREE-GAS BLOAT is often caused by physical obstruction of the esophagus, irregular feed intake, and obstruction of the contractions of the rumen walls. While it occurs less often than frothy bloat, free-gas bloat develops rapidly, offering little time to treat the animal before the condition becomes fatal. If an object obstructs the cow's esophagus, the gas in the rumen is trapped, causing acute free-gas bloat. A cow swallowing a large object, such as whole potatoes or fruit, is what causes blockage most often. Irregular feed intake can occur from inconsistent feeding, a change in the weather, a change in the cow's diet, spoiled food, or a lack of salt or water. The contraction of the rumen walls can be affected by damage to the vagus nerve, which transmits information from the rumen to the brain. Damage to the vagus nerve is caused by hardware disease.
With the constant presence of large amounts of gas in the rumen during the digestive process, bloat can develop quickly. The development of froth or foam in the rumen blocks the usual eructation process, trapping the gas inside. Without any release, the contents in the rumen expand, causing bloat. As the pressure builds in the rumen, it begins to press on the other organs. If the bloat isn't treated, the pressure will eventually inhibit lung function, and the cow will suffocate.
Unfortunately, in cattle that aren't monitored regularly, often the first sign of bloat will be a dead cow. There are certain signs to watch for, however, and if you're observant, and act quickly, bloat can be successfully treated.
Diagnosing and Treating Bloat
One of the first and most distinctive signs of bloat is distension on the left side of the abdomen. (The rumen sits on the left side.) Symptoms of a milder case of bloat may include discomfort, stomping and kicking at the abdomen, frequent urination and defecation, and labored breathing (more than what would seem normal on a warm day). As the symptoms progress, the cow will collapse, and at that point time is against you.
Bloat treatment depends on the type of bloat and its severity. There are three degrees of bloat: mild, moderate, and severe (see illustration above). Treatment for bloat is relatively straightforward, but it should involve your veterinarian if at all possible. While a veterinarian should treat the animal, the farmer should immediately remove the cow from its feed.
For mild to moderate bloat, a stomach tube can be passed through the esophagus into the rumen to relieve the gas pressure. To keep the cow from chewing on the tube, a Frick speculum should be used. This is inserted in the mouth, and the tube is passed through it. With frothy bloat, the tube may become blocked with foam once it's in the stomach. The farmer or vet should blow through the tube to clear it, and move the tube around to find pockets of gas. If this doesn't work, an anti-foaming agent, such as vegetable oil or mineral oil, may be necessary. With free-gas bloat, the stomach tube relieves the pressure almost immediately, and it's possible to watch as the rumen returns to normal size. With either type of bloat, observe the animal closely after treatment to make sure it was effective.
For severe bloat, or if previous attempts have failed, a trocar and cannula can be used. Insert the trocar--an instrument with a cutting point--into the rumen through a small incision, then remove the trocar and leave the cannula--a thin tube--in place so the froth and gas can escape.
The adage "an ounce of prevention is worth a pound of cure" is never truer than in the case of bloat.
To prevent frothy bloat in cows on pasture, ensure that the legume content of the pasture is at most 50 percent. This way, the cows can graze on grass and alfalfa to prevent bloat. But this strategy isn't effective on large pastures, or when the cows selectively graze on the legumes. The pasture and the cows should be monitored in these situations. Bloat also seems more prevalent in moist legume pastures, so wait to turn cattle out until the dew is off the plants. The extra moisture is thought to make the highly digestible forage break down even faster, and animals may eat more if forage is wet. Before turning cows out onto a pasture with legumes, feed them a good meal of dry hay to reduce their appetite and prevent overfeeding. Before putting your cows out to pasture, make a plan with your veterinarian for steps to treat any cases of bloat before they become fatal.
To prevent frothy bloat in cows in feedlots, use a coarser feed and mix in hay with the grain. Since cows in feedlots get frothy bloat due to high-concentrate rations, mixing in roughage helps to prevent bloat. To reduce the chance of bloat, the feed should be 10 to 15 percent roughage.
As much as possible, keep your cattle on a routine feed schedule, and avoid drastic changes in their diets. Drastic changes don't allow the rumen microbes to adapt.
All in all, bloat is much more successfully prevented than treated. A little knowledge of what the rumen needs and how it functions can go a long way toward keeping cows happy and healthy.
By day, Callene Rapp is a senior zookeeper at the Sedgwick County Zoo in Wichita, Kansas, and by night she manages The Rare Hare Barn with her husband, Eric. She handles all sorts of livestock and livestock challenges.
By Callene Rapp
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|Date:||Jan 1, 2020|
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