Our beef cow recently threw up lots of rumen contents, including water and partially digested hay. She is eating again, but I would like to know what can cause this?
This seems like a pretty straightforward question, but there can be several issues behind this kind of behavior.
Cows must "chew their cud" for the rumen to function properly. They regurgitate rumen contents while resting and chew this, known as "cud," for several minutes before re-swallowing it. This process is repeated over and over.
In fact, 70% or more of your cows at rest should be chewing their cud. This process grinds up grasses, hay and grains, making them more available for the rumen microbes to digest. Additionally, during this process, cows secrete large volumes of saliva, which has a high pH and is essential in preventing rumen acidosis. If the pH of the rumen gets too low, many of the microbes will die and the rumen will not function properly.
To keep the rumen healthy and happy, cows need a lot of high-quality long-stem fiber from grasses, hay and silage. Overfeeding supplemental feed or feeding very finely ground feed can lead to rumen acidosis even with adequate long-stem fiber. Poor-quality hay with low energy and protein content can also reduce rumen microbes and lead to acidosis. This acidosis can lead to "throwing up" rumen contents as you describe.
Another consideration, although very rare in beef cows, is when the abomasum, or true stomach, becomes displaced or shifts. This most commonly occurs to the left side and is called a left-displaced abomasum or LDA. This can also lead to regurgitation.
Cows will often eat feed or commodities too fast and become choked. Again, very fine feed is more of an issue. This will often cause them to forcefully cough and gag in an attempt to clear the material from the esophagus. This can occasionally occur with hay, especially poor-quality hay and is often difficult for the cow to clear. If the cow cannot clear the esophagus, this becomes an emergency situation. Here, the cow will be unable to regurgitate gas produced by the rumen, bloats and, without treatment, dies.
Lastly, any type of irritation or swelling in or around the throat or esophagus can interfere with normal regurgitation. I have seen this caused by ulcers in the mouth or esophagus, or abscesses or tumors around the esophagus.
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