Some cattle are more prone to bloat than others. The question, then, is why? “There is some thought that bloat incidence is a heritable trait,” says Carl Dahlen, Extension beef specialist at North Dakota State University in Fargo. If ranchers select for bloat-resistant animals, or at least not keep daughters from a cow or bull that bloats readily, can the incidence of fall bloat on legume pastures be reduced?

Maybe, maybe not. “Some of the heritability studies were done in New Zealand where they had a high-susceptibility line and a low-susceptibility line of dairy cattle. One of the major genes for bloat susceptibility was found to be recessive, and the high-susceptibility group did experience more bloating episodes than the low-susceptibility group. However, a portion of the cattle in the low-susceptibility group still experienced bloat, so there’s no guarantee.”

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There is evidence that some bloat-prone animals may have a lower valve between the rumen and the esophagus, more easily covered with frothy foam that results when cattle eat legume forages with a high-soluble protein content. The foam that results from the fermentation of such forage can restrict the ability to belch up gas. In addition, some research has found that certain animals’ saliva is less protective. Whatever the reason, some animals seem more bloat-prone than others.

Other reasons for bloat

In addition to legumes, such as alfalfa, bloat can occasionally occur after applying a pour-on or a drench to kill grubs in the fall. Dying grubs create swelling and inflammation around the esophagus. This obstructs feed passage and hinders belching. “Bloat can occur 10 to 24 hours following the treatment,” Dahlen says. 

“If that’s the case, and we know the animals have recently been treated, using a stomach tube to relieve bloat would not be a good idea. Forcing it down the inflamed, narrowed esophagus could damage swollen tissue. To relieve swelling, antihistamines can be administered, under a veterinarian’s direction.  In this case, a person might have to open up the rumen with a trocar and pour mineral oil in through the trocar cannula,” he says.

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