by: Heather Smith Thomas

Bloat generally occurs when there's a change to higher protein feeds, such as from grass to alfalfa, according to Dr. James England (University of Idaho Caine Center). Grasses don't normally cause bloat, but some species of grass can create bloating under certain conditions. “Usually cattle bloat when eating something that's highly digestible with high protein content, and they overload the rumen. Bacterial flora start to change and produce more gases and bacterial by-products produce a slime that traps the gas in small bubbles or froth,” he says. The cattle can't expel it (by belching) as quickly as it is produced.

“Depending on the type of feed, it may be frothy bloat, which is a mass of tiny bubbles. These can't be belched as readily, nor let out very easily by stomach tube or trocar. Rapid bloat onset interferes with breathing. The distended rumen puts pressure on the lungs and on the nerves that affect breathing,” says England. If the animal lies down there is even less room for the lungs to expand.

In most instances bloat occurs when hungry cow move into lush alfalfa pastures or overeat on newly erupted seed-heads on certain grass pastures. Don't turn cattle into these types of pastures when they are hungry, nor move them into new strips when grazing the pasture rotationally. “A lot of people pasture an alfalfa field in strips, and even though the cattle may have been on it awhile and you assume they are used to it, when you move them onto a new strip some may bloat. You always want to move them when they are full or introduce them to it slowly. It's also wise to keep bloat blocks available, and make sure the cattle are eating them,” he says.

Bloat is always an emergency, and you want to catch it early. “The usual treatment is to pass a stomach tube or hose to pass off the gas. If that doesn't work you'll need a trocar to poke a hole in the rumen to let the gas out. As a boy on our dairy farm, I can remember my mother always carrying a pair of long, sharp barber scissors. She could vent a bloated cow very quickly with those,” recalls England.

A dull trocar can be difficult to jab through a cow's thick hide. “A trocar can become dull after a few uses. You may need to make an initial slice with a sharp knife and then shove the trocar through it. If you slice through the skin you can then push the trocar through the layer of muscle and into the rumen,” he says.

“Once you vent off the gas and the rumen deflates, it shifts and may slide off the end of the trocar. This is where you run the risk of the cow getting peritonitis. Usually if it's just a small hole and the gas is pretty well vented, there isn't much leaking of fluid into the abdominal cavity,” he says. If you had to resort to slicing the rumen open with a knife, you may need your veterinarian to come sew up the cow afterward, and administer antibiotics to help prevent infection.

“The screw-in trocars work well in sheep or calves, to help keep the trocar in place, but it doesn't work as well in adult cattle. With the thicker depth of body wall (muscle) in cattle it doesn't catch and hold the rumen as well as you'd think it would. It always amazes me, every time I open up a cow's side, how thick the muscle is, under the skin,” says England.

“You need at least a four inch trocar and cannula. Most of the cannulas that come on trocars now, you can suture the side of it down so it won't pop back out. Depending on how far the rumen drops away from it as the gas comes it, it may still slide off the end of it, however,” he says.

Frothy bloat is difficult to release because the mass of bubbles tends to plug the stomach tube or trocar. “In these instances you need to administer Therabloat ® or other bloat treatment products by tube. It contains the same ingredient that's in bloat blocks, and helps break up the tiny bubbles so the gas can be released. It works a little better than mineral oil, which tends to end up on top of the rumen contents (oil being lighter than water) and can interfere with digestion,” explains England.

In some instances he has attached a stomach pump to the end of the tube, to pump out some of the frothy material. “It tends to keep plugging up the pump, but you can usually get some of the froth out and then put Therabloat® back in through the tube, to break up the rest,” he says.

Severe bloat—where the rumen is distended higher than the cow's backbone—is always an emergency. You need to relieve it quickly. Cows on lush legume pastures should be closely monitored. The rumen can continue to produce gas even up to several hours after they quit eating.

Preventing Bloat

There are several ways to minimize bloat on pastures, and these include timing of grazing, paying attention to plant maturity, soil moisture, and weather. Choose a dry day and wait until dew is off before putting animals in a new pasture. If they are first fed hay (enough to fill them up) before being put into the pasture, there is less chance for bloating; if they are full they don't overeat the lush legumes. Cattle may experience mild bloat when first turned in to a new pasture, but the problem usually disappears after a few days as they adjust.

It is safest to leave them on the pasture (unless they are bloating severely) rather than graze it intermittently. Disruption of grazing can lead to higher incidence of bloat (such as when cattle are taken out of a pasture overnight, or interrupted by storms or biting flies). Anything that disrupts their normal grazing patterns will result in more intense feeding periods afterward, which may increase the incidence of bloat.

Plant maturity is one of the most important factors in pasture bloat, so timing of grazing is crucial. Alfalfa pastures are safest when plants are quite mature. Bloat potential is highest when plants are in the prebud stage, and decreases as the plant grows and matures to full flower. Studies have shown that alfalfa 8 to 10 inches high tends to produce twice the amount of bloat as alfalfa 20 to 30 inches high.

Soil moisture makes a difference; plants with adequate moisture for optimum growth are more bloating. The stems are soft rather than fibrous, and the leaves are easily crushed between the fingers. Bloat potential of alfalfa is reduced if soil moisture is not sufficient for good growth.

Weather conditions play a role; bloat seems to occur more frequently following a cool day. Moderate temperatures (68 to 78 degrees F.) permit optimum plant growth. Cool nighttime temperatures, in combination with moderate daytime temperatures, may increase risk of bloat in the fall. Cool temperatures delay plant maturity and extend the growth phase. At the other temperature extreme, days that are hot enough to cause moisture stress and drying of plants reduced the risk of bloat.

Bloat incidence increases with cool weather, heavy dew and frost. Ranchers have thought alfalfa to be safe after a killing frost, but there is risk as long as leaves are green. The first frosts actually increase risk for bloat, preserving the immature stage of growth. The frost also disrupts the plant cells, releasing bloat-causing agents and increasing the rate of cell breakdown. It usually takes many hard freezes to render the plants safe.

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