Dealing With Pasture Bloat

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 of the 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 highly digestible feed with high protein content, and they overload the rumen. Bacterial flora starts to change and produce more gases. Bacterial by-products may produce a slime that traps the gas in small bubbles or froth,” he says.

“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 as free gas, 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 cows move into lush alfalfa pastures or overeat on newly erupted seed-heads on certain grass pastures. If cattle are hungry, don’t turn them into these types of pasture, nor move them into new strips when grazing the pasture rotationally. “Many people pasture alfalfa fields in strips, and even though 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. Always move them when they are full or introduce them to it slowly. It’s also wise to keep bloat blocks available, and make sure cattle are eating them,” he says.

Bloat is always an emergency, and you need 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, use a trocar to poke a hole in the rumen to let gas out. As a boy on our dairy farm, I 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 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 increases the risk for peritonitis. Usually if it’s 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 slice the rumen open with a knife, you may need your veterinarian to 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 not as well in adult cattle. With the thicker depth of muscular body wall in cattle it doesn’t catch and hold the rumen as well,” says England.

You need at least a 4 inch trocar and cannula.  “With most of the cannulas that come on trocars, 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 out, it may still slide off the end of it,” 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 some other bloat treatment by tube. It helps break up the tiny bubbles so the gas can be released. It works a little better than mineral oil, which tends to stay on top of the rumen contents (oil being lighter than water),” 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 that keeps plugging up the tube. “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. Cows on lush legume pastures should be closely monitored.  The rumen may continue to produce gas for several hours after they quit eating.  

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