Coccidiosis is an intestinal infection caused by protozoa and usually affects calves rather than adult cattle.
The pathogens are ingested by calves in a contaminated environment.
Most adult cattle have encountered these protozoa at some point during their lifetime and have developed some immunity, but may continue to shed a few oocysts (the “eggs” of the protozoa) in their feces, which can contaminate feed or water.
Calves are most vulnerable to the disease because they have less immunity and if they ingest a high number of protozoa, they may break with coccidiosis. The main sign of illness is bloody diarrhea.
“In baby calves we don’t see coccidiosis until they are about three weeks of age or older,” said Dr. John Campbell, department of Large Animal Clinical Sciences at the Western College of Veterinary Medicine in Saskatoon.
The incubation period — which is the time between when the oocysts are ingested until the parasite has gone through its life cycle enough to damage the intestinal lining and cause diarrhea — is about three weeks. Diarrhea in younger calves would not be due to coccidiosis.
“The main source of this pathogen for young calves is adult cows and the environment. Adult cows can have protozoa in their intestinal tracts without clinical disease,” said Campbell.
If calves are stressed due to weather issues or other problems and if their pen or pasture is crowded or has a buildup of manure, they can be exposed to significant numbers of coccidia.
After these protozoa get inside the calf’s intestine, they multiply swiftly, due to their unique life cycle.
“One oocyst can multiply to 23 million oocysts in an infected animal very quickly. A calf that ingests 50,000 oocysts can have significant clinical disease,” he said.
The dose/number of protozoa that the calf is exposed to determines the severity of clinical disease.
“The coccidia replicate within the intestinal tract and as they emerge from the intestine they damage the intestinal lining. If the infection is light, the damage can be repaired quickly by the body, but heavy infections cause more severe intestinal damage and loss of blood and electrolytes into the feces,” he said.
Minimizing or preventing exposure is the key to preventing this disease in young calves.
“Many of the things we do to prevent calf scours, such as having a separate wintering area for cows (avoiding fecal contamination of the calving area), spreading out pairs in the calving area and using a system like the Sandhills calving system or Lacombe system are all important factors for preventing coccidiosis,” said Campbell.
“We also need to prevent manure contamination in watering and feeding areas. It’s difficult to get young calves to consume enough medicated creep feed to prevent infection but we have a couple other options for reducing fecal contamination.
A drug called toltrazuril (trade name Baycox) can be given to calves as a preventive therapy. It should be given as a single oral dose prior to onset of clinical signs and has been shown to reduce the clinical signs of coccidiosis and improve weight gains,” he said.
In some cases, veterinarians may recommend an ionophore such as monensin in the cow ration before calving to reduce the shedding of coccidia oocysts in the cow herd. Both of these therapies require consultation with a veterinarian.
Calves at weaning are easier to deal with than baby calves.
“The younger calves (still nursing their mothers) usually get this disease before they are eating much solid feed,” said Campbell.
Coccidiosis can be prevented with medicated feed, but it’s harder to medicate baby calves. Even if creep fed, they won’t eat enough to be effective.
“Weaned calves, by contrast, can be on some kind of feed, or have a water source that can be medicated,” he said.
“This is primarily a disease involving confinement and hygiene. The more fecal material, the more risk. Manure build-up, over time, can be a factor in establishing infection.”
A confined group of calves is more exposed and protozoa levels build up in that group and there is more shedding of oocysts.
Death rates can be relatively high in calves that are suddenly introduced to a high level of infection, as when warm wet weather “wakes up” oocysts in manure around feeding areas — whether in springtime with baby calves, or during a wet fall with weaned calves.
If the calves don’t become re-infected, the disease runs its course, but a common problem is reinfection in a contaminated environment. Then there are parasites at several stages within the calf until the process goes on long enough that its immune system builds resistance.
A calf may have extensive gut damage that takes a long time to heal. Mild cases may have diarrhea but no blood in the manure.
“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,” Campbell said.
“Often, however, the damage is already done by the time we realize they have coccidiosis, and they must 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, you just try to prevent further damage and shedding.”
The calf may need supportive therapy, especially fluids, if it’s dehydrated from the diarrhea. Oral fluids may be necessary, and in severe cases the calf might need IV fluids. If it loses a lot of blood, it becomes anemic and weak.
If calves will be exposed to high levels of coccidian at weaning time or when groups of calves are brought together into a feedlot, this disease can usually be prevented by using an appropriate drug in the feed or water.
“There are many products used for prevention, such as adding amprolium to drinking water or adding Deccox, lasolocid or monensin to the feed. You rarely see significant coccidiosis when cattle are fed a diet containing monensin or another coccidiostat (drugs than inhibit these protozoa). These drugs do a good job of controlling it, but you might still have some sick animals if their environment is badly contaminated,” said Campbell.
Good management should be the first step.
This may mean feeding in bunks, where the feed is less likely to be contaminated with feces, and providing water in tanks or bowls that are high enough that there’s less risk for contamination. If feed bunks or water tanks get dirty, they should be thoroughly cleaned.
Weather can also be a factor in outbreaks. If everything is wet and cattle are lying in dirty bedding and then licking themselves, they may pick up heavy loads of oocysts, or may ingest them when drinking from contaminated puddles.
When cattle are gathered and brought to a confined area for weaning, this may make calves 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, however, they are exposed to more fecal material and higher level of infection.
The stress of weaning can make them more susceptible to infection. Stress hinders the immune system. This allows the parasites to divide more rapidly and go through more life cycles in the gut, creating more damage to the gut lining, before the calf can begin to resist the parasite.
“This is probably why we commonly see cases of coccidiosis at weaning, just as we see respiratory diseases. Stress plays a significant role in vulnerability, as does the confinement,” said Campbell.
If cattle can be more spread out, such as weaning calves on pasture, using fence-line weaning or some other low-stress method like using nose flaps and leaving calves with their mothers out on pasture, 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 said.