You can walk a bunch of cows all summer and never see a thing wrong. They graze, they slick off, they look bred. Then the preg-check chute in the fall tells a different story — a string of opens, and the ones that did settle scattered clear across a two- or three-month calving window. Nobody was ever sick. That pattern, more than any single dead animal, is what trichomoniasis leaves behind.
Trich is a protozoan that lives as a venereal disease in cattle. It gets passed at breeding, cow to bull to cow, and it doesn’t announce itself. There’s no fever, no snotty nose, no cow down. The damage happens early in pregnancy, weeks after she was bred, when the embryo dies and she quietly comes back into heat. From the seat of a pickup she just looks like a cow that got bred a little later than her neighbor.
Why the older bull is the problem
The bug hides in the folds and crypts of a bull’s prepuce, and it does best in an older bull. As bulls age, those folds get deeper, and a mature bull that picks up trich tends to carry it for the rest of his life without ever showing a mark. He breeds a cow, leaves the infection, breeds the next one, and spreads it through the herd one cow at a time. Younger bulls sometimes clear it on their own, but you can’t count on that, and you sure can’t tell by looking.
Cows and heifers are usually the opposite. A cow that gets infected will often clear it herself if she’s given enough sexual rest — a season off from a bull. The trouble is she doesn’t clear it fast enough to save that year’s calf. She loses the pregnancy, cycles again, maybe settles late, maybe stays open. Either way you’ve traded a calf on the ground in February for a late one in May, or none at all.
Add it up across the herd and you get the classic signature: poor conception, a calving spread that runs on and on, and a cull list of open cows that were in fine flesh all summer. It’s easy to blame the weather, the mineral, or a lazy bull. Trich rides in under all of those.
Where it comes onto the place
The two main doors are a bull you brought in and a bull that let himself in. Buying a non-virgin bull — an older bull out of somebody else’s breeding pasture — is the fastest way to import it. A guaranteed-virgin bull that’s never bred a cow can’t carry it. That’s the whole appeal of turning out clean, young bulls, and of buying from an outfit that tests.
The other door is the fence. A neighbor’s bull that walks through a wire down in the timber in May can breed a handful of your cows and be gone before you know he was there. If his herd has trich, now yours does too. This is the unglamorous reason to ride your boundary fences before and during the breeding season, and to sort out any strange bull the day you find him instead of “getting to it.”
There’s no shot that prevents trich the way blackleg vaccine prevents blackleg, and there’s no treatment worth talking about in a bull. The tool that works is testing. A vet takes a preputial scraping and runs a culture or a PCR test, and it usually takes more than one sample to call a bull clean, because the bug doesn’t shed evenly. Many states, Montana included, tie testing to the sale and movement of breeding bulls — check the current rules with your vet or brand office before you buy or sell, because those requirements change and vary by situation.
What actually holds the line
Testing is the front end. The back end is management, and it costs you almost nothing.
- Run a defined breeding season instead of leaving bulls out year-round. A tight window gives cows the sexual rest they need to clear the infection and shows you fast when conception falls apart.
- Preg-check every fall and cull the opens and the very late cows. Don’t roll an open cow forward and don’t keep a chronic late-bred as a “maybe.” She’s the reservoir for next year.
- Lean toward young, guaranteed-virgin bulls, and be careful about turning bought cows or bred females out with your herd until you know their history.
- Keep the fences up and keep strange bulls out. One wandering herd bull can undo a clean program in a week.
Trich is a slow, quiet loss. It doesn’t kill a cow in the pasture where you can point at it — it takes the calf months before it would have been born, and it takes it from enough cows that you feel it at weaning and at the sale barn. Test the bulls, keep the fences tight, and cull the opens, and you starve it out. Ignore it, and you’ll spend a couple of Novembers wondering where your calf crop went.
