I’ve written a lot in past blogs about the amazing physiology of the cow. From cud chewing to massive milk production, the bovine is an impressive feat of engineering, for sure. But, as with most biological systems, there are occasional design flaws.


Take the rumen. This giant fermentation vat, encompassing the majority of the bovine’s upper digestive system, is home to billions of microorganisms that break down the grass and hay the cow consumes. If you looked at a functioning rumen in cross-section, you would notice there are layers to its contents; this is called the compartmentalization of the rumen. At the bottom of the rumen is a liquid layer. This is the most-digested stuff — food that’s been sitting in there the longest, waiting to pass into the intestines. The layer on top of that is called slurry — sort of a mix between liquid and solid. This is the almost-digested stuff. On top of the slurry is the solid layer. This is the stuff just-chewed, the hay and grass, creating a mat that floats on top. Above this mat is gas, the by-product of all the fermentation going on inside.


Normally, the “gas cap,” as it’s called, floats happily at the top of the rumen with periodic escapes through the esophagus. Bovines burp (the medical term is eructate) a lot because of this. But what happens what that gas cap can’t escape? You get a bloated cow.


There are two ways a cow can bloat. One type occurs if the esophagus is physically obstructed, preventing the release of gas. The second type, called frothy bloat, occurs when the cow has consumed a lot of lush legume grass such as clover or alfalfa. The consumption of a large quantity of rich legumes creates foam in the rumen that sits on top of the gas cap. The small bubbles in this foam prevent the cow from burping and releasing gas.


If the gas is not released either mechanically through passing of an orogastric tube or chemically via administration of a surfactant that breaks down the froth in a way not dissimilar to soap detergent, the animal will die.


I have encountered bloat occasionally. One case particularly sticks out in my memory.


One afternoon, a client called in a panic about her daughter’s 4H show steer. She reported that he seemed bloated and wasn’t sure what to do. I came right out and found an ornery steer and a frantic and frazzled client who had just struggled to get the steer into the chute.


I brought out my orogastric tube and was quickly feeding it down the steer’s mouth through a metal speculum. I looked over at the client, discussing how sometimes you’ll be able to hear the gas rushing out of the tube when suddenly: POW! A wad of partly chewed cud flew out of the tube onto the shoulder of the client, followed by a huge rush of air.


“WOW!” I said, relieved at the instantaneous and very satisfying resolution of the problem at hand.


“ARGGGGG!” yelled the client in horror at the unexpected lump of grassy goo on her person.


I couldn’t help it. I burst out laughing. I mean, who wouldn’t, right?


After the initial shock subsided and the client realized her steer was back to normal, she, too, started laughing. Thank goodness for clients with a sense of humor! To add to the humorous mayhem, after complaining that this steer “had a mind of his own” and was the “most ornery steer I’ve ever dealt with,” the steer mostly dragged the client out of the chute and back to the pasture gate.


After making sure said steer was safely put away and the client hadn’t been yanked around too harshly, I giggled my way back to my truck. Who knew bloat could be so entertaining?


Dr. Anna O'Brien


Image: smereka / Shutterstock