The frustrating thing about anaplasmosis is the delay. A tick or a horse fly picks up the organism off one carrier cow and hands it to another sometime in June, and nothing happens. No fever you’d catch, no cough, no limp. Then three, four, even six weeks later a good mature cow quits the bunch, stands off by herself breathing hard, and when you push her she comes at you instead of moving off. By the time you see trouble, the insect that started it is long gone and the damage is done inside her.
It’s a blood disease. Anaplasma marginale gets into red blood cells and the cow’s own immune system tears those cells apart trying to clean house. That’s what makes her anemic. The membranes around her eyes and her gums go pale, then take on a yellow cast as things get worse. She’s weak, she’s short of air on any hill, and a lot of the aggression people notice is just an oxygen-starved animal that feels cornered. Push a cow that far along too hard and she’ll die from the handling before the disease finishes the job.
Who gets hit, and who carries it
Age is the cruel part. Calves and yearlings that get exposed usually shrug it off with mild or no clinical signs. Cows two years and older are the ones that get sick, and cows past three or four are the ones that die. So the disease skips the young stock you could most afford to lose and takes the mature, proven cows and herd bulls you can’t replace with a phone call.
An animal that survives becomes a lifelong carrier. She looks completely normal and never gets sick again, but her blood stays loaded, and she’s the reservoir every biting fly and tick works off of the next summer. That’s why anaplasmosis tends to settle into a place once it arrives and stay there. It’s showed up in parts of Montana, more in the eastern and southern country, and it’s the kind of thing that can ride in with purchased cattle you didn’t know were carriers.
You spread it as much as the flies do
Ticks and biting flies get the blame, and they earn it. But a fair share of transmission is human-caused, and it all happens at the chute. One needle used down a whole run of cows carries blood from animal to animal as sure as any horse fly. Same with a dehorning tool, an ear tagger, a tattoo pliers, or a castrating knife that goes from one animal to the next without cleaning. If you’ve got a carrier in the herd and you’re using single-use tools on the whole crew, you’re doing the disease’s work for it.
- Change needles often, and never share a needle across a group of adult cattle if you can help it.
- Clean and disinfect anything that draws blood between animals during working.
- Keep the fly and tick pressure down through the season with whatever program you already run.
- Be careful bringing in outside cattle, and ask what the source herd’s status is.
Why June matters
The vectors ramp up as the weather warms, so June and early July are when most of the transmission that shows up in late summer actually takes place. That’s the window to get out ahead of it. In herds and regions where anaplasmosis is a known problem, feeding a low level of chlortetracycline in mineral or feed through the vector season is the common tool for holding clinical cases down. That’s a medicated feed decision that runs through your veterinarian now under the feed directive rules, so if it’s something you need, that’s a call to make before the season is on top of you, not after.
Treating an animal that’s already clinical is a different conversation, and a touchy one, because a badly anemic cow can drop dead from the stress of being gathered and run through the chute. If you find one standing off, breathing hard, pale and yellow around the eyes, the smart move is to leave her be and get your vet on the phone rather than to rope and drag her to the corral.
Anaplasmosis is easy to blame on bad luck because the cause and the sickness are weeks apart. They’re not really disconnected, though. The needle you reused at branding and the flies you let build up in June are still working in August. Handle both while it’s early and cheap, and you keep your old cows old.
