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Lamb with coccidiosis


Coccidia can infect many animals, but especially mammals and birds. Coccidiosis is one of the most economically important diseases of sheep. It is caused by microscopic, single cell protozoan parasites of the genus Eimeria. With few exceptions, coccidia are host-specific meaning there is no cross-infection between hosts. Even sheep and goats are infected by different species of coccidia. None cause disease in people.

At least 11 species (maybe more) of coccidia are known to infect sheep, but only two are known to be highly pathogenic: Eimeria crandallis and Eimeria ovinoidalis.  Pathogenic species such as these affect both the small and large intestine. The other species which infect sheep are not known to cause any disease issues. At some point in their life, almost all sheep are exposed to coccidia and shed oocysts in their feces. However, most sheep, even lambs, are asymptomatic, as they usually develop immunity to coccidia at an early age.

Life cycle
Coccidia have a direct life cycle, meaning no other animal or organism is involved. Their life cycle is more complex than nematodes (worms). As with other parasites, there is a free-living stage (exogenous) which takes place outside the animal and a parasitic phase (endogenous) which takes place inside the animal (in the gut). Within the gut, there is both an intracellular and extracellular component. Coccidia undergo both sexual (gametogony) and asexual (schizogony) reproduction. The duration of the life cycle is 2 to 4 weeks, depending upon the species of Eimeria.

The egg-like structure of coccidia is called an oocyst (not be confused with an oocyte, which is an immature female reproductive cell). Oocysts are extremely resistant to environmental stress, including ordinary disinfectants. They have a thick wall that protects them. However, they can be killed by heat (sunlight and drying) or extreme cold (freezing). This is why pasture is a less favorable environment than enclosed housing. However, oocysts can overwinter on pasture in small numbers. They can survive for months in the soil.

The coccidia life cycle starts when oocysts are shed in the feces of infected animals. If conditions are conducive (warmth + humidity + oxygen), the oocysts “sporulate” (mature) and become infective. Animals ingest infective oocysts. Once in the gut, the oocysts break open, releasing high numbers of parasites, which invade the gut wall.

Each parasite grows by asexual reproduction to produce a hundred or more “daughter” parasites. The daughter cells break out and invade fresh areas of the gut wall. Within 10 to 14 days, the parasites have multiplied by up to a million-fold. By this stage of infection, parts of the gut wall are packed with parasites, which develop into male and female sex cells. Oocysts are shed in the feces, starting the cycle all over again.

From the sheep’s perspective, clinical symptoms do not usually appear until late in the life cycle. At each stage of the cycle, intestinal cells are invaded and destroyed, causing repeated damage to the intestine. The intestinal damage can release blood and cause inflammation of the lining of the gut. Villi (finger-like projections that increase nutrient absorption) are damaged. The animals lose blood, water, and protein and cannot absorb nutrients as efficiently. Coccidiosis can cause permanent damage to the animal's digestive tract. Some animals may never thrive, despite treatment. Some die.

As with other gastro-intestinal parasites, immunity is acquired with a gradual exposure to the parasite. Sheep develop immunity to coccidia sooner than nematodes (roundworms). However, if exposure to coccidia overwhelms the animal’s immune system, clinical disease results. This is particularly true of young lambs, whose immune systems are still developing. Disease is rare in adult animals, but they serve as reservoirs of infection.

Transmission is the oral-fecal route. Lambs become “infected” when they consume sporulated oocysts. Fecal contamination of hay, grain, bedding, pasture, udders, teats, water troughs, and feeders (especially creep feeders) are all sources of infection. Environmental build-up of coccidia occurs in the barn and dry lot, as well as areas on pasture. Transmission of coccidiosis to lambs favors warm and wet environmental conditions. Clinical disease often erupts during the transition from winter to spring.  Outbreaks are often related to seasonal changes in rainfall. Extreme weather can trigger disease.

While there is disagreement as to whether colostrum provides newborns with protective immunity to coccidiosis, very young lambs (< 3 weeks) are not usually affected.  Lambs, 1 to 6 months of age, are at greatest risk for coccidiosis. Those under 3 months of age are most commonly affected, though older lambs may exhibit poor performance, due to earlier infections. Coccidiosis affects both nursing lambs and growing lambs that have been weaned.

Disease outbreaks are most common in intensively-managed flocks. While coccidiosis is considered more of a risk with housed animals, intensive grazing situations can create similar environmental conditions, resulting in disease outbreaks. Overcrowding (or stocking) is one of the primary risk factors associated with outbreaks of coccidiosis. Coccidiosis is often seen with other diseases, such as pneumonia and sore mouth (orf).


As with many diseases, there are two forms of coccidiosis:  subclinical (chronic) and clinical (acute or severe). Subclinical coccidiosis often goes unnoticed, as symptoms may not be apparent. Mostly, subclinical coccidiosis reduces performance (growth and feed conversion) of lambs. It is the most common form of the disease and most costly. Clinical coccidiosis is when disease symptoms are observed. Without effective treatment of clinically-parasitized animals, serious damage or death can occur.

Diagnosis of coccidiosis can be difficult, as other diseases present with similar symptoms and fecal oocyst counts are not a reliable method of diagnosis, at least not by themselves. When making a diagnosis, factors to consider are epidemiology (who, when, and where), clinical signs, fecal oocyst counts (and speciation), response to treatment, and post-mortem examination of animals.

Coccidiosis should be suspected any time there are digestive problems in young animals that are being raised under intensive conditions. The most common sign of coccidiosis is scours (diarrhea). Feces are usually brown and soft. They may be foul-smelling. Liquid (watery) feces are common with severe infections. Sometimes, feces are smeared with blood or mucous.

Affected lambs exhibit symptoms consistent with ill thrift:  lethargy, weakness, anorexia, dehydration, loss of weight and body condition. A hollow, hunched-up appearance is common among clinically-parasitized lambs. Lambs may strain to defecate, which could result in rectal prolapse. They may experience abdominal pain. Their abdomen may be distended (pot-bellied). Fever is not common, but parasitized lambs may have pale mucous membranes (anemia). Severe infections could result in death.

Fecal oocyst counts (OPG) aid in diagnosis, but are not a definitive method of diagnosis, because there is not always a strong relationship between oocyst counts and the severity of disease. Large numbers of oocysts (e.g. 100,000 OPG) have been found in animals that are unaffected, while (clinical) disease may be present in animals with few oocysts in their feces.

The other reason fecal oocyst counts are not a definitive method diagnosis is because not all coccidia are pathogenic. To be useful, fecal analysis should include speciation. However, this is seldom done, except under research conditions. Despite the general relationship between clinical coccidiosis and oocyst excretion, no threshold for treatment has been established, though a fecal oocyst count of >20,000 OPG of a pathogenic species is considered characteristic of coccidiosis in lambs.

A necropsy is the most reliable method of diagnosis. The most common finding is multiple, raised white lesions on the intestinal mucosa. 1 to 6 mm in diameter. Thickening of the intestinal wall, due to edema, is not uncommon. In acute cases, the intestinal lumen may contain blood. The coccidia organisms themselves cannot be seen at necropsy, as they are microscopic.


As with other diseases, prevention of coccidiosis is far more cost effective than treatment. This is because by the time clinical signs have appeared, most of the damage has already been done.

Good hygiene
Prevention starts with good husbandry practices, especially sanitation. Since coccidiosis is transmitted in the manure, it is important that animals be raised in hygienic conditions. Pens should be stocked according to industry recommendations. In fact, it is probably a good idea to exceed space requirements. The barn or birthing facility should be cleaned before lambing. Pens need to be kept clean and dry. In intensively-managed sheep operations, it may be necessary to bed daily.

Removal of soiled bedding is ideal, but generally not practical. Moreover, excessive cleaning of cement floors may be more conducive to organism survival, as moisture is more likely to accumulate in a thin layer of manure. Frequent clean-out is generally not necessary if the bedding on the top of the manure pack is clean and dry. It is especially important to keep lambing jugs clean. Ideally, jugs should be cleaned and limed between births. Slatted floors will greatly reduce transmission of coccidia.

Feeders need to be kept free from fecal matter. Designs which prevent fecal contamination should be favored. Fence line feeders are a good way to minimize fecal contamination. Hay can be fed in racks. It may be necessary to cover hay racks to keep animals out. A horizontal bar will help to keep lambs out of creep feeders. Elevated feeders are preferred to feeders at ground level. Open troughed feeders are especially problematic, as lambs like to play and sleep in them. Feed pans or troughs should be removed or turned over after feeding. No feed should be fed on the ground. Water receptacles must also be kept free from fecal contamination. Areas around water troughs need to be kept dry. Leaky waters need to be fixed. Water should not be allowed to overflow.

Good nutrition
Good nutrition is essential to maintaining high levels of immunity in all animals. Good nutrition starts with colostrum (the first milk). Pregnant ewes should be fed to optimize the quality and quantity of colostrum that they produce. Ewes in good body condition will produce more milk and better-quality colostrum than ewes that are thin. Mature ewes usually produce better colostrum. Land O’Lakes markets a colostrum substitute if ewe’s milk is insufficient.

Lambs need to consume adequate amounts of colostrum. Even if the colostrum doesn't provide specific antibodies to coccidia, it improves the lamb's immune function. The sooner colostrum is consumed, the better. Colostrum is only produced for the first 24 hours by the ewes. The lamb’s ability to absorb antibodies diminishes with time. Absorption is most efficient in the six hours after birth. The recommended consumption of colostrum is 10 to 15 percent of body weight. Colostrum can be fed with a bottle or tube fed to at-risk lambs or those whose dams lack sufficient colostrum.

Balanced rations, with the appropriate amounts of energy, protein, vitamins, and minerals, should fed to all animals at all times. There is software that can be used to balance rations. Animals in better body condition are better able to tolerate parasite and disease challenges. Body condition score can also be used to make treatment decisions. It is part of the Five Point Check©.

It is important that there is always enough feeder space. In fact, it’s never a bad idea to exceed industry recommendations for feeder space. Competition for feeder space is an added stress. Young lambs should not have to compete for feeder space with older, bigger lambs. When there is not enough feeder space, it is always the smaller, weaker lambs that will be pushed out.

Because coccidiosis is frequently observed in newly-weaned lambs, it is essential that weaning be carried out as stress-free as possible. Weaned lambs should always be kept in familiar surroundings, with their same pen-mates. It is the ewes that should be moved to another location for drying off. While fence line weaning may be advantageous to other species, it does not appear to reduce the stress level in lambs.

It is important that lambs be consuming the same diet after weaning, as they were consuming before weaning. Lambs of different age and management groups should not be mixed, especially at the time of weaning. Tight birthing periods make it easier to batch manage lambs. To avoid additional stress, any management practice should be performed prior to weaning.

In extensive production systems, pasture rotation will help to minimize exposure to infective oocysts. Lambing should take place on clean, well-drained pastures. Avoid grazing in low-lying areas and near streams and ponds. Since animals tend to defecate near water troughs, it may help to move water troughs and feeders around. Low stocking densities will go a long way towards preventing outbreaks of coccidiosis on pasture.

Because coccidiosis is often seen with other disease conditions, it is important to control other diseases in the flock. Anything that lowers the immunity in the lamb will make it more susceptible to coccidia infection. It can be too difficult for lambs to fight more than one disease at a time. There are vaccines for pneumonia and sore mouth. Ventilation is key to controlling respiratory problems in housed animals. Be aware of the build-up of ammonia in the barn. Ewes and lambs should be vaccinated for clostridial diseases. Foot rot should be controlled or eliminated (ideally) from the farm. There are numerous strategies for controlling other gastro-intestinal parasites.

Outbreaks of coccidiosis are often associated with shipping (transportation) stress. Ideally, newly-weaned lambs should not be shipped. When transportation is required, industry recommendations should be followed. Lambs should be loaded using low stress handling techniques. They should not be overcrowded in trucks and trailers. Lambs should not be worked or transported in the heat of the day.

Intensive production (pens)
Extensive production (pasture)

Clean barn before lambing
Clean jugs between births
Tight birthing periods
Batch manage lambs
Clean, dry bedding
Good nutrition
Adequate intake of colostrum
Good disease management
Avoid overcrowding
Timely use of coccidiostats
Well-designed feeders
Adequate feeder space
Low-stress weaning
Minimize stress

Clean, well-drained pastures
Pasture rotation
Avoid "hot spots" on pasture
Move feeders and waterers
Avoid overstocking
Timely use of coccidiostats
Good nutrition
Adequate intake of colostrum
Good disease management

Genetic control

There is some evidence that some breeds and individuals are more resistant to coccidia infections and that heritabilities are similar to nematode (worm) resistance. However, data is lacking, as far less research emphasis has been placed on protozoan parasites, as compared to nematodes. So far, no long-term selection studies have been conducted. 

Repeatability estimates for oocyst counts suggest that selection for resistance to coccidia should be theoretically possible. At the same time, it would be difficult to select simultaneously for resistance to both worms and coccidia, unless a favorable genetic correlation was determined, or a selection index developed. In fact, it has been hypothesized that animals that are more resistant to extracellular parasites (worms) may be more susceptible to intracellular parasites (coccidia).

Using coccidiostats
While there is no vaccine for coccidiosis (for sheep), coccidiostats can be added to feed, mineral, water, and milk replacer to aid in the prevention of coccidiosis. There are two coccidiostats approved for use in sheep. Lasalocid (Bovatec®) is an ionophore antibiotic. It can be fed to sheep maintained in confinement. Decoquinate (Deccox®) is a non-antibiotic coccidiostat. It can be fed to lambs.

A form of Deccox® is added to some milk replacers (e.g. Pipestone). Monensin (Rumensin®), another ionophore, is not FDA-approved for sheep, but has been fed to sheep, under the supervision of a veterinarian. Monensin is highly toxic to horses. Mixing errors have caused toxicity in lambs. Bovatec® has a lower risk of toxicity than Rumensin®. Deccox® is the safest to use.

Coccidiostats have an effect on different stages of the coccidia life cycle. The ionophores kill coccidia, whereas Deccox® prevents its growth. Bovatec® kills the “free living” stages of coccidia, as they move from cell to cell in the intestine, while Rumensin® works on three different stages of development. Deccox® provides the widest range of activity of all the coccidiostats. When used properly, all of the coccidiostats can reduce oocyst output significantly, while allowing lambs to develop immunity to coccidia.

The effectiveness of coccidiostats depends upon two key factors: timing and dosage. Coccidiostats must be fed early in the coccidia life cycle before the onset of clinical signs (usually 3-4 weeks ahead of time). Coccidiostats must be consumed at sufficient (labeled) levels. Adequate consumption is challenging since coccidiostats are often contained in free choice feeds or mineral. Consumption of feed by lambs can be variable. Underdosing is a big problem in nursing lambs. Forage consumption further reduces intake of the drug. As lambs get older, it may necessary to change the feed mixture to make sure they are consuming the proper amount of the coccidiostat.

Coccidiostats should be fed strategically. They should not be fed year-round, as year-round use may increase the probability of resistance. Anecdotal reports suggest that some farms may have resistance to Bovatec®. It is common to feed a coccidiostat to ewes during late gestation, though there is disagreement as to whether this is a necessary management practice. The rationale is that feeding a coccidiostat will reduce contamination of the lambing area, thereby reducing exposure of the lambs. There is evidence that there is an increase in oocyst excretion (similar to worms, though not as high) by the periparturient ewe.

Feeding ionophores in late pregnancy may have an added benefit of reducing exposure to toxoplasma gondii, cat coccidia (the only coccidia species that is not species-specific). Toxoplasmosis is a common cause of abortion in ewes. Other potential benefits of coccidiostats may include increased feed efficiency, enhanced growth rate, and reduced incidence of free-gas bloat.


Once a diagnosis has been made, it is important to initiate treatment immediately to prevent permanent damage and death losses. All animals sharing the same space should be treated. Anthelmintics (dewormers) do not have an effect on coccidia. The drugs that are used to prevent coccidiosis are not same ones that are used to treat clinical disease. Currently, there are no drugs FDA-approved to treat coccidiosis in sheep. Extra label drug use is required.

Extra label drug use is when a drug is used in any manner that is not listed on the product insert or label. For example, Corid® is not labeled for sheep. A different dose or route of administration also constitutes extra label drug use, as is using a drug to treat a disease that is not listed on the label. Only licensed veterinarians have the right to use or prescribe drugs extra label. For a producer to use a drug extra label, a valid veterinarian-client-patient relationship (VCPR) must exist. This usually means that the veterinarian must have familiarity with the farm and the animals treated. It is important that all producers comply with extra label drug requirements.

Amprolium (Corid®) is used to prevent and treat coccidiosis in sheep. It is added to the drinking water (as a preventative) or administered as a drench (as a treatment). The dilution is different, depending upon the intended use: prevention vs. treatment. Corid® is considered more effective as a treatment, as it acts late in the coccidia life cycle, after coccidia have already done some damage. There is anecdotal evidence that there is resistance to Corid® on some farms, especially goat farms.

While Corid® can be purchased over-the-counter at a feed or farm supply store, it is not labeled for sheep. Therefore, its use requires veterinary supervision. Corid® is usually given for 3 to 5 days. It has a unique mode of action. It mimics thiamine (vitamin B1). For this reason, care should be taken when using it, as there is some risk of polioencephalomalacia (thiamine deficiency) with high doses and prolonged use.

Sulfonamides such as sulfamethazine (Sulmet®) or sulfadimethoxine (Di-Methox®) are the other drugs commonly used to treat coccidiosis in sheep. As with other water-soluble antibiotics, sulfa drugs must be obtained from a veterinarian and used under veterinary supervision. Like Corid®, sulfa drugs are added to the drinking water or administered as a drench. Drenching is always preferable, as it ensures that an animal, especially a clinically-parasitized one, gets the proper dose of the drug. Sick and nursing animals are not likely to drink enough water for treatment. Three to five days is the usual treatment duration. There is some toxicity risk with sulfa drugs if they are overdosed or used for prolonged periods. Animals should be weighed to make sure a safe and effective dose is administered.

Lambs that are treated may require additional supportive care, such as re-hydration. Probiotics may help with appetite. After treatment they should be moved to a clean pen, either a pen with clean bedding or an uncontaminated pasture. Good nutrition should be provided.

While producers are fortunate to have medical choices for treatment and control of coccidiosis, the emphasis should be on management options, aimed at reducing exposure to the infective organism and improving immunity of the animal.

Drug Tradename Dose Comments
 Amprolium Corid® Varies Not approved for sheep
 Decoquinate Deccox® 0.5 mg/kg Approved for young sheep
 Diclazuril Clinacox®
1 mg/kg Not approved for sheep
Approved in other countries
 Lasalocid Bovatec® 20-30 g per ton of feed
15-70 mg/head/day
Approved for confined sheep
 Monensin Rumensin® 20 g per ton of feed Not approved for sheep
 Ponazuril Marquis® Consult vet Not approved for sheep
 Toltrazuril BayCox®
20 mg/kg Not approved for sheep
Approved in other countries
 Sulfaquinoxaline Sulmet® Varies Not approved for sheep
 Sulfadimethoxine Albon®
Varies Not approved for sheep
Unapproved drugs require extra label drug use and a valid veterinary-client-patient relationship

Other drugs
Experimentally, ponazuril has been used to treat coccidiosis in kid goats. A single dose (10 mg/kg) was found to as effective at reducing oocyst counts as a five-day treatment of Corid® (50 mg/kg). Ponazuril is a metabolite of toltrazuril. In the US, it is available as Marquis®, a paste used to treat protozoal myeloencephalitis in horses.

Outside the US, there are other treatment options. Totrazuril (BayCox®) and diclazuril (Vecoxan®) are licensed in Europe and other countries for the control of coccidia in sheep (and calves). Toltrazuril (20 mg/kg) is usually effective as a single treatment, whereas diclazuril (1 mg/kg) may require two treatments. Research has shown toltrazuril to be a more effective treatment option as compared to diclazuril, as it has a longer duration of action. Farm history dictates when to give both drugs, as they should be given prior to the onset of symptoms. Toltrazuril has a very long withdrawal period (48 days for lambs), whereas diclazuril has no meat withdrawal. Toltrazuril can be obtained in the US, but it is illegal to use.

Natural control
Researchers continuously search for more "natural" methods to control internal parasites, including coccidiosis. One of the most promising is sericea lespedeza. Sericea lespedeza (Lespedeza cuneata; CL) is a perennial, warm season legume, often called “poor man’s alfalfa," because it can be grown under sub-optimal soil conditions. It can be grazed or fed as hay, silage, or (leaf meal) pellets. Considerable research has demonstrated the effectiveness of SL in the control of Haemonchus contortus (barber pole worm). More recently, researchers have discovered that SL has a similar effect on coccidia. Lambs consuming SL diets have lower oocyst counts and less clinical signs (of coccidiosis) than those consuming control diets. It is the condensed tannins in SL that give it its anti-parasitic properties.

To aid in the control of coccidiosis, researchers recommend that lambs be fed a SL diet 1 to 2 weeks prior to weaning and for 3 to 4 weeks after weaning. Continuous feeding of SL is not recommended, due to potential anti-nutrition factors. Unfortunately, SL pellets are not widely available, and when they are available, they can be pricy. The only company ( that produces SL pellets is located in Alabama.

Oregano and other essential oils have shown some promise in the control of coccidiosis, especially in poultry. More research is needed before they can be recommended as control options for sheep. Because the poultry industry is so much larger and coccidiosis is a wider spread problem, this is likely where “natural” prevention/treatment options will emerge. There are commercial vaccines for coccidia control in poultry. The nematode-trapping fungus Duddingtonia flagrans sold as BioWorma® unfortunately has no effect on the life cycle of coccidia.



Late updated 19-Apr-2021 by Susan Schoenian.
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