You can lose a good mature cow to anaplasmosis and never see it coming. She’s fat, she’s bred, she raised a calf last fall — and one morning in August she’s standing off by herself, breathing hard, and by the time you walk up on her she’s down. The disease has been in your herd for months. The flies and ticks of summer just finished the job.
Anaplasmosis is caused by a tiny organism, Anaplasma marginale, that gets into red blood cells and destroys them. The animal’s body tears down the infected cells faster than it can build new ones, and the cow ends up severely anemic. Everything that follows — the weakness, the heavy breathing, the staggering — comes from blood that can’t carry enough oxygen.
Why it shows up when it does
The bug spreads three ways, and all three peak in summer. Ticks carry it. Biting flies — horse flies, stable flies, the same crew already working your cattle over — move infected blood from one animal to the next. And you can spread it yourself with a dirty needle, a castrating knife, dehorning gear, or a tattoo plier that went from one animal straight to the next without cleaning.
There’s a long lag between infection and sickness. A cow bitten in May or June may not break with clinical signs until late July, August, or into September. That delay is why anaplasmosis catches people flat-footed. By the time cows are going down, the transmission happened weeks earlier and you can’t undo it.
The cruel part is which animals it hits. Calves and yearlings usually shrug it off with little more than a mild infection — and then they carry it for life. It’s the mature cows, the three-year-olds and up, that develop full-blown disease and die. The older the animal, the worse it tends to be. So the disease quietly works through your young stock without symptoms, then takes out the productive heart of your cow herd.
What it looks like in the pasture
Early signs are easy to miss because they look like a cow that’s just off. She drops back from the herd. She’s slow. Milk falls off and her calf looks gaunt. As the anemia deepens, you’ll see pale gums and a yellow cast — to the whites of the eyes, the gums, the vulva — from the breakdown of red blood cells. She breathes hard with any effort. Bred cows can abort.
One thing every hand needs to know: an anaplasmosis cow that’s badly anemic can turn aggressive and unpredictable. Her brain isn’t getting oxygen and she may come at you or a horse. More important, stress and exertion can kill her outright. If you rope, run, or rough-handle a cow in the late stages, you can finish her off before any treatment has a chance. Move suspects slow, or leave them and bring treatment to them.
If you’ve got a cow showing these signs, get your veterinarian involved. Long-acting oxytetracycline is the standard treatment, but it works best caught early, and a vet can confirm what you’re dealing with — anemia and jaundice can come from other causes too.
Keeping it out, or keeping it down
Once anaplasmosis is established in a herd, you’re managing it, not eradicating it, because carrier animals stay infected for life and keep the cycle going. A few things actually move the needle:
- Change needles often. One needle per animal is the gold standard at working time; at minimum, change frequently and never share blood-contaminated needles across the chute. Disinfect knives, dehorners, and tattoo pliers between animals — that’s good practice for a pile of reasons, and anaplasmosis is one.
- Stay after the flies. Your horn fly and biting-fly program isn’t just about gain and pinkeye; fewer biting flies means fewer chances to move infected blood. Tick control where ticks are a problem helps the same way.
- Know where new cattle came from. Bringing in carrier animals — bulls especially — is a common way the disease arrives on a clean place. Testing can identify carriers if you’re trying to keep a herd free of it.
- Talk to your vet about feeding chlortetracycline through the vector season. In herds with a known problem, a medicated mineral or feed program during fly-and-tick months can hold clinical cases down. That route requires a Veterinary Feed Directive now, so it runs through your veterinarian — get that conversation started before the cows start breaking, not after.
The mistake that costs the most is treating anaplasmosis as a one-off — doctoring the cow that went down and moving on. She didn’t get it alone. If one mature cow breaks in August, others in that group are likely infected and may be days behind her. Walk your older cows in the heat of summer with this in the back of your mind, and watch for the one hanging back, breathing hard, with that yellow look around the eyes.
