Bloat in Cattle: Causes and Response

Bloat is a build-up of gas in the rumen that can kill a cow in a short time. This guide covers why it happens, how to lower the risk and what to do first, which is to call your veterinarian.

Key points

Bloat is trapped rumen gas and can be fatal quickly.
Frothy bloat is tied to lush legumes, wheat pasture and rich diets.
Free-gas bloat points to a blockage or belching problem.
Call the veterinarian first and avoid home methods.
Prevention is gradual introduction, dry hay beforehand and close watching.

Why cattle bloat

Cattle normally produce a lot of gas as they digest feed, and they get rid of it by belching. Bloat happens when gas cannot escape. The rumen swells on the left side and presses on the lungs and heart, and an animal can die from the pressure.

There are two main types. Frothy bloat is when gas is trapped in a foam. Free-gas bloat is when gas collects above the rumen contents, often because something blocks the throat or the cow cannot belch.

Cattle that gorge on rich feed can also bloat on grain, so the same watchfulness applies to feedlot rations and to any time hungry animals find an unexpected feed source, such as a broken fence into a crop field.

Frothy bloat and the feeds behind it

Frothy bloat is the type linked to lush legume pastures such as clover and alfalfa, and also to wheat pasture and high-grain diets. Certain plant compounds and fast fermentation help form stable foam that the cow cannot belch away.

Risk is highest when hungry cattle are turned onto lush, wet or frosted legume pasture. The first hours of grazing matter most, but problems can show up at other times too.

Free-gas bloat

Free-gas bloat is usually caused by a blockage or a nerve or muscle problem that interferes with belching. A calf with a chronic issue may bloat on and off. A choking cow may have something stuck in her throat.

A vet should look at any animal that bloats repeatedly or without an obvious feed link. Chronic cases can point to an underlying problem.

Recognizing it early

Walk through the herd after turning onto risky pasture and at regular intervals after. A swollen left flank is the classic sign, but behavior changes first.

Move calmly. Rushing cattle can make a bad case worse, and a severely bloated animal can drop without warning.

Check cattle at the times of day when the risk is highest, and make it a habit to count heads and look at every left flank, not only the animals that are standing near the road.

Swelling on the left side behind the last rib
Discomfort, kicking at the belly, repeatedly getting up and lying down
Open-mouth breathing, drooling or extended tongue
Staggering or collapse
Found dead and swollen after grazing risky forage

What to do right away

Call your veterinarian immediately and describe what you see. The vet will tell you whether to bring the animal in, what to do on the spot and how to prevent more cases. Do not attempt to relieve a bloated animal with home methods, improvised tools or products you have heard about from others. Mistakes can injure the animal or cause infection.

If many animals are affected, ask the vet whether to remove the herd from the pasture right now and what to offer in its place. Keep calm, quiet handling a priority.

Prevention with pasture and feeding management

Prevention is a planning job, and your veterinarian and nutritionist can design a program for your pasture. Concept-level steps include not turning hungry cattle onto lush legume stands, filling cattle with dry hay before turnout, introducing risky pasture gradually, and mixing legumes with grass.

Some operations use approved anti-bloat products or feed additives. Those must be used under label directions and professional guidance. Do not use rates passed along by neighbors.

Share the emergency number for your vet with your family and crew, and post it where it can be found in a hurry, along with directions to the pasture in case someone else has to guide a vet truck in.

Feed dry hay before turning onto lush pasture
Avoid turning hungry cattle onto legume-heavy fields
Increase time on risky forage gradually
Check herds closely during the first days of exposure
Keep a written plan and an emergency vet number handy

Common mistakes

Frequent mistakes are moving the herd to a lush field late in the day with no check afterward, assuming a calm herd is a safe herd, and reaching for a home remedy before calling the vet. After any case, record the field, the weather, the forage and the time so you and your vet can adjust. Follow withdrawal times on anything given to treated animals.

When to get help: Call your veterinarian right away for any swollen, distressed animal, and ask the vet and a nutritionist to help design a bloat prevention plan for your pastures. Any anti-bloat product must be used exactly as labeled and with professional guidance.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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