Death losses from pasture bloat are estimated to be approximately 2% annually but are sometimes much higher (10% to 20%) on individual pastures.
“Costs of bloat include not only losses of livestock but also decreased productivity from avoidance of the most nutritious pastures due to bloat risk,” says Michelle Arnold, DVM and University of Kentucky ruminant extension veterinarian. “Bloat incidence varies year-to-year depending on the relative presence or absence of clover; years with low residual grass cover in the fall, especially after fall drought, and sufficient moisture in the spring will favor clover dominance.”
Frothy bloat occurs when cattle graze forages high in soluble protein and low in fiber, most commonly pastures with a high percentage of immature legumes (alfalfa, white clover) or succulent, vegetative wheat or rye pastures.
“This disorder is caused by the interaction of many factors including environmental conditions, the structural and chemical composition of the forages present, and physiologic factors within the animal,” Arnold explains.
Because it is multifactorial, frothy bloat occurrence is sporadic, unpredictable and difficult to completely prevent. It is most reported when cattle, especially yearlings, graze legume or legume-based pastures (over 50% legumes) in the late winter and early spring.
What is Bloat?
Ruminant animals produce large volumes of gas through the normal fermentation process during forage digestion. This gas is predominantly belched (eructated) or it passes through the gastrointestinal tract. If something interferes with gas escape from the rumen, pressure builds up and causes an obvious distension in the left flank of the abdomen, a condition known as bloat.
The swollen rumen occupies a large amount of space within the abdomen resulting in compression of the lungs and diaphragm, which interferes with breathing and tissue oxygenation, obstruction of blood flow to vital organs and potentially the rapid death of the animal. Bloat may be classified into one of two types — free gas or frothy — with both possible in cattle whether on pasture or in a confinement feedlot setting.
Free gas bloat in pastured cattle is most often due to obstruction of the esophagus (choke) with rapid onset of bloat and death if not addressed quickly. Free gas bloat from choke can be relieved by passing a tube down the esophagus into the rumen, simultaneously clearing the esophageal obstruction and releasing the trapped gas.
Frothy bloat, on the other hand, results when fermentation gases become trapped within a stable foam in the rumen (like the head of a beer) and the animal is no longer able to belch up the gas. Simply passing a tube into the rumen will not solve the problem, because the froth prevents gas from leaving the pressurized rumen. For effective relief, anti-foaming agents must be delivered directly into the rumen to disperse the foam and allow the gases to escape.
Frothy Bloat Characteristics
Frothy bloat results when fermentation gases become trapped in a stable foam in the rumen that cannot be released by eructation. Requirements for this foam to form are:
- Consumption of a highly digestible, high-protein forage (such as alfalfa, white clover, wheat) that results in rapid gas production, promotes the growth of ruminal microbial populations and increases rumen fluid viscosity.
- The presence of fine plant particles (from ruptured chloroplasts) that cause gas bubbles to coalesce in rumen contents.
- Active ruminal bacterial production of an excessive amount of bacterial “slime” (a mucopolysaccharide complex also known as a biofilm).
“The incidence of bloat is variable between animals and depends on the individual animal’s rate of forage fermentation and production of ruminal gas, the digesta passage rate and the foaming properties of rumen contents,” Arnold says.
For example, a slower passage rate allows more time for foam formation and a higher chance of bloat. Similarly, the abundance of certain salivary proteins within saliva decreases that animal’s formation of rumen foam.
“Some animals have a genetic predisposition to bloat, and chronic bloaters should be culled,” Arnold says.
Signs of Bloat
According to Arnold, the signs of bloat are easily recognized if observed; the problem is an animal may go from normal to dead within an hour.
Cattle with early bloat display a distended left flank, and they stop grazing, may kick at their belly and be reluctant to move.
As bloat advances, the animal may appear distressed (may vocalize, eyes may bulge), stand up and lie down repeatedly, strain to urinate and defecate, exhibit rapid and open mouth breathing, grunting, staggering and, in advanced cases, the animal will go down.
“Death is rapid at this stage due to compression of the lungs, diaphragm and major organs by the distended rumen,” Arnold says. “Animals that are mildly affected can be drenched orally or through a stomach tube with a liquid anti-bloat preparation containing the surfactant poloxalene. After dosing, it is encouraged to keep the animal moving to allow the preparation to mix with the frothy rumen contents.”
Severely bloated animals in distress need immediate veterinary attention. Arnold says this may be achieved by inserting a wide bore trocar and cannula into the rumen at the highest point on the left flank (where the swelling is greatest).
“After gas and froth is released, an anti-bloat preparation can be poured through the cannula into the rumen to help break down all remaining froth/foam,” she explains. “If poloxalene is unavailable, vegetable oil (250-500 mL) or mineral oil (100-200 mL) can be used.”
In most cases of advanced frothy bloat, a trocar and cannula will quickly plug up with foam and will not be adequate to relieve the pressure.
“In those cases, a 10-to-20-cm incision will have to be made using a scalpel or clean, sharp knife inserted into the highest point of the left flank,” Arnold says. “It may be necessary to manually remove the frothy material from the rumen. In these emergency cases there is usually no time to wait for a vet to arrive, so livestock owners will have to do this themselves. Veterinary attention is still necessary to irrigate the abdominal cavity, clean and stitch the wound and begin antibiotic treatment to prevent serious infection.”
Prevention Tips
Arnold shares these tips to help prevent frothy bloat:
- Avoid grazing cattle on lush, rapidly growing, immature legume or wheat pastures. “This is exceptionally important if the forage is wet from dew or rain,” she says. “Moisture plays a role in a forage’s bloat potential. Hungry cattle graze more aggressively when moved to a new pasture, so they should not be moved to new pastures with high legume content until midday — after the dew has dried and after they have grazed or consumed hay in the morning.”
- Watch cattle closely for the first few days on new pasture. “Bloat onset may be observed within an hour after introduction to new pasture, but cattle more commonly bloat on the second or third day following introduction,” she says. “Observe animals closely following any abrupt change in the weather.”
- Slow the movement of cattle to new paddocks when practicing rotational grazing to offer cattle more mature forages in pastures.
- Provide cattle with free-choice access to anti-bloat blocks or offer feed daily that is top-dressed or mixed with poloxalene.
- Ensure cattle always have palatable grass hay available.
- Provide additional calcium to growing cattle grazing wheat pasture. “Cereal grains are notoriously low in calcium; ruminal and gut motility is greatly compromised in animals with subclinical deficiencies of blood calcium,” she says.
- Always provide a good trace-mineral mix to grazing cattle as high potassium and low sodium levels in the rumen are associated with bloat.
- Provide access to a clean water source.
- Long-term control is based on growing grass-legume mixtures and/or incorporating bloat-resistant legumes into pastures.
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