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Eimeria bovis


Mike Taylor

Andrew Forbes

Synonym(s): Coccidia, coccidiosis




  • Phylum: apicomplexa.
  • Class: conoidasida.
  • Family: eimeriidae.

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Clinical Effects



  • High stocking densities and intensive husbandry systems with overcrowding in unhygienic yards or feedlots lead to a build-up infective oocysts and disease outbreaks.
  • Year round calving can present problems with constant use of calf pens with successive batches of young calves added to pens or buildings already housing older calves.
  • The season of the year can play a role in the appearance of coccidiosis Coccidiosis.  
  • Coccidiosis is common in spring when young calves are born and turned out onto permanent pastures close to the farm buildings. Inclement weather at this time may cause stress at this stage lowering immunity and precipitating disease.
  • Cold winters favor survival of overwintering oocysts in large enough numbers to represent sufficient disease challenge at turn out in spring; conversely mild wet springs favor sporulation, and rapid accumulation of large numbers of infective oocysts.
  • Autumn born calves may be born into an already heavily contaminated environment.
  • Stress factors, such a poor milk supply, weaning, cold weather and transport, will reduce any acquired resistance and exacerbate the condition.


  • Following ingestion of the sporulated oocyst, the released sporozoites each penetrate an epithelial cell, round up, to form a trophozoite.
  • After a few days each trophozoite has divided by multiple fission (merogony) to form a first generation “giant”meront (schizont), each consisting of a large number of elongated nucleated organisms known as merozoites.
  • The first-generation meronts are in the endothelial cells of the lacteals of the villi in the posterior half of the small intestine.
  • The meronts mature at 14-18 days post infection; the host cell and the meront rupture and the merozoites escape to invade neighbouring cells forming second generation meronts.
  • Second-generation meronts occur in the epithelial cells of the caecum and colon, but may extend into the last metre of the small intestine in heavy infections.
  • Sexual reproduction (gametogony) generally occurs in the caecum and colon, but may extend into the ileum in heavy infections.
  • The prepatent period is 16–21 days and the patent period usually 5–15 days.


  • The host becomes infected by ingestion of sporulated oocysts.
  • The sporocysts are liberated either mechanically or by carbon dioxide, and the sporozoites, activated by trypsin and bile, leave the sporocyst infecting epithelial cells in the ileum.

Pathological effects

  • The most severe pathological changes occur in the cecum, colon and terminal foot of the ileum, due to the presence of large numbers of gamonts.
  • The mucosa appears congested, edematous and thickened with petechiae or diffuse hemorrhages. The gut lumen may contain a large amount of blood.
  • Later in the infection the mucosa is destroyed and sloughs away. The submucosa may also be lost.
  • If the animal survives, both the mucosa and submucosa eventually regenerate.

Other Host Effects

  • Infection causes diarrhea or dysentery with tenesmus in heavy infections. Affected calves may be pyrexic, weak and dehydrated, lose condition and may die.


Control via animal

  • Good feeding of dams prior to parturition and creep feeding of calves helps boost resistance to coccidiosis.
  • Adequate intake of colostrum Colostrum in the first 24 hours from birth is very important in providing passive immunity until about 4 weeks of age.
  • Calves develop a strong immunity to coccidia but the immunity is species-specific and dependent on continual exposure to oocysts.

Control via chemotherapies

  • Controlling coccidiosis is a balance between preventing disease, whilst at the same time allowing the development of protective immunity through adequate parasite exposure.
  •  Treatment interventions should aim to prevent pathology and disease, but allow protective immunity to develop through adequate exposure of the hosts’ immune systems to the parasite stages.
  • The timing of treatment interventions should be based on epidemiological evidence and knowledge of anticipated disease outbreaks on farms.
  • Clinically affected animals should be medicated and moved to a cleaner environment or uncontaminated pasture as soon as possible.
  • Usually all calves in a group should be treated as even those showing no symptoms are likely to be infected.
  • The most commonly used licensed treatments are:
    • Diclazuril Diclazuril (Vecoxan) given as a single oral drench at 1mg/kg.
    • Toltrazuril Toltrazuril (Baycox) given as a single oral drench at 20 mg/kg.
    • Decoquinate Decoquinate (Deccox) given as an in feed at an inclusion rate of 1mg/kg for 28 days
  • Both diclazuril and toltrazuril can also be given as a preventative by administering prior to periods of anticipated risk of disease outbreaks following a period of stress such as weaning.
  • Other anticoccidials such as amprolium, monensin Monensin or lasalocid may be available in some non-European countries.
  • Whilst sulphonamides (sulphadimidine, sulphamethoxopyrine etc) have been widely used in the past, they no longer have a licensed claim for the treatment of coccidiosis in cattle.
  • Supportive therapy may be required depending on clinical presentation.
  • Fluid therapy Fluid therapy and astringents may be required to control diarrhea.
  • Antibiotics may be indicated for concurrent bacterial infections.

Control via environment

  • Hygiene plays a major part in the control of coccidiosis and to achieve effective control good management and hygiene is vital.
  • The incidence of disease can be reduced by simple measures such as providing dry bedding and avoidance of overcrowding and stress.
  •  Other measures that can be taken include reducing stocking densities, batch rearing of calves and avoidance of mixing different age groups.
  • Keep young animals off heavily contaminated pastures when they are most susceptible.
  • Regularly moving food and water troughs, and raising or covering them to prevent faecal contamination, can help reduce the levels of infection.
  • It is good practice to clean and disinfect all buildings between groups of animals or provide clean pasture for calves turned out to grass.

Other countermeasures

  • Steam cleaning or pressure washing helps remove fecal debris and it is important to use a disinfectant that claims activity against coccidial oocysts, as not all disinfectants will kill oocysts. 


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Phillipe P, Alzieu J P, Taylor M A & Dorchies P (2014) Comparative efficacy of diclazuril (Vecoxan®) and toltrazuril (Baycox bovis®) against natural infections of Eimeria bovis and Eimeria zuernii in French calves. Vet Parasitol 206, 129-137 PubMed.
  • Zechner G, Bauer C, Jacobs J, Goossens L, Vertenten G & Taylor M A (2014) Efficacy of diclazuril and toltrazuril in the prevention of coccidiosis in dairy calves under field conditions. Vet Rec 176, 126 PubMed.
  • Taylor M A (2000) Protozoal Disease in Cattle and Sheep. In Practice 22, 604-617.
  • Taylor M A & Catchpole J (1994) Coccidiosis of Domestic Ruminants. Applied Parasitology 35, 73-86.

Other sources of information

  • Taylor M A, Coop R L & Wall R L (2016) Chapter 8 - Parasites of Cattle: Bovine Coccidiosis. In: Veterinary Parasitology. 4th edn. John Wiley & Sons, UK. pp 369-378.
  • Enemark H L, Dahl J & Enemark J M D (2015) Significance of timing on effect of metaphylactic Toltrazuril treatment against eimeriosis in calves. Parasitol Res 114 (1).
  • Taylor M A (2004) 1.4.1 Antiprotozoals. In: The Veterinary Formulary. 6th edn. Royal Pharmaceutical Society of Great Britain and British Veterinary Association, UK. pp 171-179.

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