Coccidiosis is a protozoan disease that exists wherever there are cattle. Nearly all cattle carry a few of these parasites in their digestive tract. Most cattle have encountered these protozoa and have developed some immunity, but may continue to shed a few oocysts (the egg form of the protozoa) in feces, which may contaminate feed and water. Calves are most vulnerable to the disease because they don t yet have immunity. If they ingest a high number of protozoa in a dirty environment, they may develop the disease.
After calves reach six months of age they ve all been exposed, though only two to five per cent will have shown symptoms, according to research studies. At weaning, when cattle are gathered and congregated, especially if calves are confined in a corral or feed yard, calves may be exposed to more manure and coccidia, and some may break with coccidiosis.
If they ve been out on large pastures, calves may have been exposed to a few protozoa, but not enough to cause disease. When the group is gathered and confined, however, they are suddenly exposed to more fecal material and a high level of infection and the stress of weaning may hinder the immune system. The best defence against this disease is good management, preventing situations in which contamination can build up to infective levels.
Steve Hendrick, an assistant professor of Large Animal Clinical Sciences at the Western College of Veterinary Medicine (WCVM) in Saskatoon, says that any time you confine cattle there will be greater exposure. At weaning time the calves are more at risk for respiratory diseases and also for coccidiosis, he says.
If hygiene is poor (such as allowing feed or water to be contaminated with feces), it doesn t take long for all the calves to be exposed. Some develop clinical signs such as a dirty hind end or blood in the manure. Diarrhea in newly weaned calves may be the result of a drastic change in feed, but often it s a sign of coccidiosis, says Hendrick.
Clinical signs can vary from subtle to very severe. A calf may merely have a slightly looser stool, but in severe cases the calf may become quite dehydrated, with sunken eyes, he says. These calves may become so weak that it s hard for them to get up.
When a group of calves becomes exposed to high levels of oocysts (the egg stage of protozoa, passed in the manure), you generally see a large number of animals with messy diarrhea, but only a few animals are severely affected. Once a few individuals break with diarrhea, however, they are spreading millions of oocysts and there is more risk for contamination of feed and water, and the whole group is soon exposed.
John Campbell, head of the Department of Large Animal Clini- cal Sciences at WCVM, says that the more fecal material, the more risk for disease. The strategies for dealing with coccidiosis are largely preventive. We don t have very effective treatments. Most calves recover on their own, but we do treat them and attempt to accelerate healing. Often, however, the damage is already done by the time we realize they have coccidiosis, and they have to heal on their own. 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 re just trying to prevent further damage and shedding, says Campbell.
The calf may need supportive therapy, especially fluids, if he s dehydrated from diarrhea. Oral fluids may be necessary, and in severe cases the calf might need IV fluids. Drugs for coccidiosis include coccidiostats like amprolium, decoquinate, and sulfa drugs, but these work better for prevention than treatment. There is no best treatment, but there are several options. Producers should discuss this with their veterinarian to try to decide what might be best in their own situation.
There are many products used for prevention, such as adding amprolium to the drinking water or adding Deccox, lasolocid or monensin to feed. We rarely see much coccidiosis when cattle are fed a diet containing monensin or another coccidiostat (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, says Campbell. Good management should be the first step.
This may mean feeding up off the ground in bunks, where cattle are less apt to defecate on the feed and avoiding contamination of water bowls. Weaned calves can be easier to deal with than baby calves, because we don t have some of the licks for cows containing monensin (available in the U.S.), which can be an advantage in reducing the coccidia load in baby calves. Some producers try to treat the cows so they are passing fewer oocysts in their manure.
Calves at weaning are somewhat easier to deal with than baby calves that get coccidiosis. The younger calves usually get it before they are eating much solid feed, says Campbell. 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. Weaned calves, by contrast, can be on feed, or have a water source that can be medicated, he says.
You won t see diarrhea right away when calves get coccidiosis. The incubation period is about three weeks from the time the animal ingests the protozoa until breaking with diarrhea. It takes awhile before you see the clinical signs, says Campbell.
The oocysts multiply within the animal to high levels and create the gut damage that leads to diarrhea. The calf will eventually fight the pathogen and develop some immunity. Calves get over the diarrhea, but in a severe case there s so much intestinal damage that the calf may lose weight and won t start gaining again for a while.
If the disease is chronic and ongoing, you see some very stunted calves. Some people call this big head disease because the calf is much older than its body size looks, says Hendrick. More often the disease is subtle and the calf just doesn t gain and grow as well as it would have.
Weather can play a role in disease outbreaks. Bad weather creates more stress, and if cattle are bedding on wet, contaminated straw or hay, and then lick themselves, they pick up a high number of protozoa. Calves may ingest oocysts when drinking from contaminated puddles. Wet weather and contamination of feed grounds and calving areas can also bring on coccidosis in baby calves.
When ranchers have experienced outbreaks in baby calves, they may try to treat the cow herd before calving (adding a coccidiostat to the cows feed, to prevent proliferation of protozoa in the intestinal tract and halt extensive shedding of oocysts in the feces). The hope is to clean out the cows and minimize contamination of the environment for young calves. Ranchers might try this before weaning time putting the calves on medicated creep feed before they are weaned and exposed to high levels of coccidia. It s hard to know whether this would be economically feasible, says Hendrick. In situations where producers have had severe outbreaks at weaning time, however, this might be something to consider.
Some ranchers may not be able to utilize creep feed before weaning time. In a feedlot situation, by contrast, where feed and water can be controlled, a coccidiostat might be more readily added to the feed or water. Before weaning it may be difficult to get enough of the medication into calves especially if they are young and are not used to eating grain or supplemental feed, he says.
One way to reduce the problem of coccidiosis is to minimize stress as much as possible. At weaning, calves often get put through the chute and vaccinated. If a lot of procedures (vaccination, deworming, castration, dehorning, etc.) take place at this time, this is stressful. And if you are putting calves through a chute, they are head to tail, and some of the calves may be shedding oocysts in their feces. The calves behind them may become exposed. Ranchers need to realize there is some risk involved, says Hendrick.
The best way to address this issue is to vaccinate at a different time (ahead of or after weaning), to reduce stress and exposure, he says. It may be difficult for a rancher to work the animals twice, but it s wise to spread out these stresses and not have it all happen at once.
Low-stress weaning methods, such as fence line weaning, pasture weaning, or use of nose paddles (that keep calves from nursing their mothers) can often help prevent disease in weaning-age calves. We haven t done studies with the nose paddles to prove there would be less incidence of coccidiosis or shedding, but I think the lower stress might be helpful, says Hendrick.
I am sure stress plays a significant role in vulnerability, as does confinement, says Campbell. If the cattle can be more spread out, such as weaning the calves on pasture, using fenceline weaning or some other low-stress method, 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.