Weaned calves more susceptible to coccidiosis due to low immunity, new environments

Protozoa in a contaminated environment cause coccidiosis, a common intestinal disease.
    Most cattle have encountered these protozoa and have developed some immunity, but may continue to shed a few oocytes, or the egg-form of the protozoa, in their feces, which may contaminate feed or water.
    Calves are vulnerable to the disease because they don’t yet have much immunity, and if they ingest a high number of protozoa in a dirty environment, they may break with coccidiosis.
A look at coccidiosis
    This intestinal infection can cause diarrhea and weight loss, along with lowered resistance to other diseases. Calves may have blood in the manure, anemia and emaciation.
    In an outbreak, most animals in a group become infected, but usually only a few show symptoms. In a serious outbreak, up to 80 percent of the group may develop clinical illness.
    Among those showing symptoms, mortality rate can be as high as 10 to 15 percent unless calves are treated in early stages. In calves that don’t show symptoms, subclinical infection may reduce weight gains until the intestine is fully healed.
    Mortality rates can be high in calves with no previous exposure if they are suddenly introduced to a high level of infection, such as when calves are put into contaminated weaning pens or shipped to feed yards. Many outbreaks occur during the first 30 days calves are in feedlot or weaning areas, especially if wet conditions stimulate development of oocysts that are shed in manure.
    “Calves at weaning are somewhat easier to deal with than baby calves that get coccidiosis,” says John Campbell of the Department of Large Animal Clinical Sciences at Western College of Veterinary Medicine in Saskatchewan, Canada.
Treatment and prevention
    Coccidiosis can be prevented with medicated feed, but it’s harder to medicate baby calves because even if you try to creep feed them they won’t eat enough of it to be effective, he says.
    “Weaned calves, by contrast, can be on some kind of feed, or have a water source that can be medicated,” he says.
    “This is largely a disease involving confinement and hygiene. The more fecal material, the more risk for disease. Manure build-up, over time, can be a factor in establishing infection. A confined group of calves becomes more exposed, the protozoa level builds up in that group, and there is more shedding of oocysts,” he says.
    If a calf is born during dry weather out on pasture, he won’t encounter coccidia and won’t build immunity and may break with coccidiosis in the fall when exposed to more contaminated conditions.
    Calves that picked up a few oocysts in the spring might not have enough infection to break with the disease themselves but may still serve as a source for other calves at weaning time, on winter pasture if they grouped together as stockers, or over-wintered as replacement heifers.
Addressing coccidiosis
    “The strategies for dealing with coccidiosis are preventive. We don’t really have very effective treatments. Most calves recover on their own, but we do treat them and attempt to accelerate healing,” Campbell explains.
    “Often, however, the damage is already done by the time we realize they have coccidiosis, and they have to heal on their own,” he continues. “We can try to prevent further damage, but we can’t do much for what has already happened with the parasite damaging the gut wall. By the time you see bloody diarrhea, the calf must deal with that, and we are just trying to prevent further damage and shedding.”
    The calf may need supportive therapy, especially fluids, if he’s become dehydrated from the diarrhea. Oral fluids may be necessary, and in severe cases the calf might need IV fluids.
    “There are many products used for prevention, such as adding amprolium to the drinking water or adding Deccox, lasolocid or monensin to the feed,” Campbell says. “You rarely see significant coccidiosis when cattle are fed a diet containing monensin or another coccidiostat, which are drugs than inhibit these protozoa. These drugs do a pretty good job of controlling it, but you could probably still have some sick animals if their environment is badly contaminated.”
Management strategies
    Good management should be the first step.
    “This may mean feeding up off the ground in bunks, where the cattle are less apt to defecate on the feed, and avoiding contamination of water troughs,” Campbell comments.
    Weather can also be a factor in outbreaks.
    Campbell explains that, if everything is wet, and the cattle are lying in dirty bedding and then licking themselves, they are more apt to pick up heavy loads of oocysts or may ingest them when drinking from contaminated puddles.
    “The incubation period is about three weeks from the time the animal ingests the protozoa until breaking with diarrhea. Thus it takes awhile before you see clinical signs,” he says.
    Cattle that are gathered and brought to a confined area for weaning become more vulnerable. If they’ve been out on large pastures they may have been exposed to a few protozoa, but not enough to cause disease. When the group is gathered and confined, they are suddenly exposed to more fecal material and a high level of infection, along with the stress of weaning which can hinder the immune system.
    “This is probably why we commonly see cases of coccidiosis at weaning time, just as we might see respiratory diseases. I am sure that stress plays a significant role in vulnerability, as does the confinement,” says Campbell.
    If cattle can be more spread out, such as weaning calves on pasture, using fence line weaning or other low-stress methods, these risks may be reduced.
    “Anything you can do to lower the stress at weaning could be helpful, but calves can still get coccidiosis without stress if the environment is dirty. The stress, however, could make it worse,” he explains.
    Heather Smith Thomas is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.