Most of the trouble a Montana cowherd runs into in June you can see. A cow’s lame, a calf’s coughing, a bull comes up sore. Anaplasmosis isn’t like that. It moves quiet all summer, and the first hard evidence a lot of producers get is a good older cow found dead in September with nothing obvious wrong, or one that turns belligerent and staggers when you push her into the corral. By then the thing has been working in the herd for weeks.
It’s worth understanding now, in vector season, because June is when the flies and ticks start moving the disease around and when the few management decisions you can make actually matter.
What it does and why old cows pay for it
Anaplasmosis is caused by a blood parasite that gets inside red blood cells and destroys them. The animal’s own system clears the infected cells, and the cow ends up anemic. A young calf can carry it and barely blink. The older the animal, the harder it lands, which is why this disease has a habit of killing your best mature cows and your herd bulls rather than the calves.
The signs come from lack of oxygen. A sick cow drops off feed, gets weak, and falls behind the herd. Her membranes go pale and can turn yellow as things progress. Some get aggressive and hard to handle right before they go down, because a low-oxygen brain doesn’t think straight. Bred cows can abort. On summer range, a lot of the deaths just show up as cattle found dead in a draw, and it’s easy to blame something else.
Here’s the part that makes it stick: an animal that survives becomes a lifelong carrier. She looks fine, breeds back, raises calves, and stays a reservoir the rest of her life. That’s usually how it walks onto a place that never had it. You buy a nice older cow or a bull at a sale, she’s a carrier, and the following summer the flies do the rest.
How it gets from one cow to the next
Two roads. The first is biting insects and ticks. Horn flies, horse flies, stable flies, and ticks pick up infected blood off a carrier and carry it to the next animal. You can’t spray your way completely clear of that, but a herd getting hammered by flies is moving a lot more blood around than one that isn’t. Every reason you already have to knock down horn flies applies double where anaplasmosis is a concern.
The second road is the one you actually control, and it’s the one that gets overlooked: blood on your equipment. A needle used on a carrier and then run into the next ten head. A dehorner, a tattoo pliers, a castrating knife, an ear-tagger, a bander gone through a whole calf crop without cleaning. It takes only a trace of blood. If you processed cattle this spring and reused a needle across the bunch, you moved blood the same way a horse fly does.
- Change needles often when you work cattle, and don’t share one across a bunch of adults.
- Disinfect dehorners, knives, and taggers between animals when you can.
- Keep after fly control through the whole vector season, not just once in June.
Feeding through the fly season
On places where anaplasmosis is established, the common approach is feeding chlortetracycline in the mineral or feed through the vector months to hold the disease in check. That’s a real tool and a lot of eastern Montana outfits use it. Two things to know before you count on it. One, medicated feed-grade chlortetracycline now requires a Veterinary Feed Directive, so you need your vet involved and the paperwork in order before you buy it. Two, cattle have to actually eat enough of the mineral to get the dose, and you already know how they walk off the mineral feeder when the grass greens up. A feeder that sits empty or gets ignored isn’t protecting anything.
Talk to your veterinarian about whether your country and your herd warrant it. If you’ve bought outside cattle, especially mature cows and bulls from areas where anaplasmosis runs, tell your vet that too. It changes the risk picture more than anything else on the place.
The disease is easy to miss until it’s costing you cows. The prevention is unglamorous — cleaner needles, steady fly control, a mineral program the cattle actually use. None of it will show up as a win you can point to. It just shows up as the September you don’t spend dragging dead cows out of the brush.
