Adult cattle are rarely affected by coccidiosis, but they pass the parasite eggs, called oocysts, in their manure. They serve as a source of infection for calves who have not yet gained enough immunity to fight off this protozoan parasite. Calves can become ill if they pick up large numbers of oocysts.

The best defense against coccidiosis is preventing situations in which contamination builds up to infective levels. Stress allows the parasite to divide more rapidly and go through more life cycles in the gut. If a calf's immune system is hindered by stress, the number of cycles is greater before he can begin to resist the parasite, creating more damage to the gut lining.

Death rates can be high in calves suddenly introduced to a high level of infection, as when warm wet weather "wakes up" oocysts in old manure around feeding areas. The incubation period from the time the calf ingests oocysts until breaking out with diarrhea is 16 days or longer. By day 18 or 19, the calf has diarrhea and there may be blood in the feces, and by day 21 there are oocysts in the manure.

If calves don't become reinfected the disease runs its course; the big problem is reinfection in a contaminated environment. Then there are parasites at several stages within that calf until the process goes on long enough that his immune system begins to build resistance. The calf may also have extensive gut damage that takes a long time to heal. If he loses a lot of blood he's anemic and weak. Supportive treatment fluids by stomach tube or I.V. may be needed. Mild cases may have diarrhea but no blood in the manure.

Matted hair on the rump (as seen on these two calves) is a sure sign all is not well. Keeping feeding areas clean will do a world of good.

Feeding hay provides ideal conditions for coccidiosis in baby calves if cattle are grouped in feeding areas, such as when fed round bales. Ranchers should manage cattle in ways that help prevent contamination of pastures, and minimize stress on calves. It helps to keep group size small.

Best prevention is having cattle spread out on good pasture or to keep changing the feed area. Then oocysts passed in manure are widely scattered over a large area; calves don't pick up enough to cause massive infection. They encounter the parasite and begin to build immunity, but don't get enough to develop the disease.

If the same feeding areas are reused during wet weather, you are feeding on contaminated ground. The cows are continually passing a few oocysts, which stay dormant in manure for a while if weather is cold. When it warms up, the oocysts become infective. Calves who lie on manure and then lick themselves, or suck a dirty udder, are exposed to high levels of infection. Move cattle to new ground when possible, getting them away from areas of concentrated manure, or continually move the bale feeders.

If coccidiosis shows up in calves, get them away from the source. Move the cattle, feed in a different area, or put them in a fresh pasture. Use of small pens often leads to manure buildup and infective conditions.

Cows pass a small number of oocysts, but if a young animal is sick it spreads thousands. It is always better to try to prevent coccidiosis than to treat it after calves get sick. Several drugs are effective against coccidiosis if given before symptoms appear, and less effective after a calf is already sick; supportive treatment may be necessary to save him. Your vet can recommend a treatment program. In a group of confined calves, all the calves should be treated, even if they are not all sick.