You turn pairs onto a good stand of alfalfa or clover mixed pasture in June, come back a couple hours later, and one cow is standing off by herself with her left side ballooned out past her hips. That’s frothy bloat, and it doesn’t give you much time to think about it. A cow can go down and die within an hour of the first sign, sometimes faster. It’s one of the quicker ways to lose an animal that looked perfectly healthy at breakfast.
The trap with bloat is that it shows up on your best feed. Lush, fast-growing legumes—alfalfa, red and white clover, sometimes even young sweetclover—are exactly the pastures you want cattle on for gain. But those same plants ferment fast in the rumen and produce a stable foam that traps gas. The animal can’t belch through the foam, pressure builds against the diaphragm and lungs, and she suffocates from the inside.
When and Where It Bites
Early summer is prime time in Montana, especially the first few days cattle go onto a new legume stand. Wet, growing forage is worse than mature or wilted forage. A heavy dew, a frost, or a stretch of cool cloudy weather that keeps plants tender all raise the odds. So does moving hungry cattle onto that pasture midmorning after they’ve had nothing much overnight—they’ll gorge, and the fresh, wet growth goes down fast.
Pure grass pastures rarely cause frothy bloat. It’s the legume component that drives it, so irrigated meadows and hayfields you’re grazing after a cutting are the spots to watch. Alfalfa in the vegetative-to-early-bud stage is the highest risk. Once it flowers and coarsens up, the danger drops, though it never goes clear to zero.
Keep Them From Blowing Up in the First Place
Prevention beats treatment by a mile here, because treatment often means you’re already out in the pasture with a dead cow and two more looking bad.
- Fill them up before they go in. Never turn hungry cattle onto lush legume pasture. Feed hay first, or let them clean up a grass paddock, so they walk in with a full rumen and take the green stuff a little at a time.
- Feed a bloat blocker. Poloxalene is the standard—it breaks up the foam so cattle can belch. It comes in blocks, in loose mineral, or top-dressed on feed. The catch is cattle have to actually consume enough of it every day, so watch that the whole bunch is hitting the block and not just the boss cows. Start it a few days before you turn onto the risky pasture.
- Introduce the pasture gradually. Turn out for an hour or two the first day, then pull them, and build up over several days. Rumen microbes adjust, and cattle that have been on legumes a while handle it far better than fresh ones.
- Graze it when it’s drier. Wait for the dew to burn off before turning in. Grazing a mixed stand with more grass in it, or letting alfalfa get to bloom, both cut the risk.
Don’t count on any one of these alone. A poloxalene block does no good if the cows won’t eat it, and a full rumen only buys you so much on a heavy dew.
When One’s Already Blown Up
Check cattle often the first several days on new legume pasture—morning, midday, and evening—because that’s when trouble starts. The signs are hard to miss once you know them: a distended left side that’s tight as a drum, drooling, stamping, an animal that won’t move with the others, and finally open-mouth breathing and staggering. When she goes down, you’re nearly out of time.
Mild cases can sometimes be walked slowly to relieve gas, and there are commercial anti-foaming drenches made for bloat that work if you get them in early. In a genuine emergency with a cow going down, a trocar or a cut into the rumen at the left flank can save her life, but that’s a last resort and a messy one—know how and where before you’re standing over a dying cow trying to figure it out. Better to have your vet’s number handy and the drench in the barn than to be learning field surgery in a panic.
The honest answer is that once you’re treating bloat, you’ve already lost the easy part of this fight. The producers who don’t lose cattle to it are the ones who filled bellies before turnout, kept the blocker in front of them, and eased the herd onto that rich green feed instead of throwing the gate wide on a hungry bunch. Green grass in June is money in the bank, but only if you let them eat it on your terms.
