Coccidiosis in Cattle


Coccidiosis is a gastro-enteric disease affecting calves (as well as other animals) caused by a single-celled protozoon parasite which causes severe damage to the lining of the gut and subsequent diarrhoea. It is mainly a disease of young animals before they have developed immunity. The disease is much less common or severe in older animals.

Diarrhoea is a common condition in young calves and can be due to a number of different factors. Pathogens such as viruses (rotavirus, coronavirus), bacteria (E.coli, Salmonella), parasites (worms) as well as nutritional factors can all be involved. Apart from the immediate health impacts, and calves can die from dehydration if not treated appropriately, it has been demonstrated that there are longer term effects on productivity. Calves with more episodes of diarrhoea when they reach reproductive age, may be older at their first calving, require more inseminations, have lower milk yield and are more likely to be culled early. Clearly, it’s important to manage calf scours in order to preserve both short term and long term health and productivity.


Coccidiosis is an infection caused by 2 species of coccidia, Eimeria bovis and Eimeria zuernii. These are widely spread in Australia, are very contagious and highly resistant to environmental conditions. Younger calves between 3 weeks to 6 months of age are worst affected and stress is a contributing factor. Regrouping or rehousing, changes to feeding (e.g. weaning) or climatic changes can all precipitate an outbreak.

After ingestion of oocysts from the environment, the oocysts release intermediate stages which invade and multiply in the cells lining the calves’ intestine. This stage cause the gut damage which results in the signs of disease.

Calves can show a number of signs. Some are subclinical (i.e. not overtly obvious) such as loss of appetite, weight loss, poor condition and slightly loose faeces. Others may be more seriously affected and show bloody or dark faeces, presence of shreds of intestinal lining in the faeces, abdominal pain and on occasions, death possibly associated with secondary infections. A key point to keep in mind is that by the time signs appear, the damage to the gut has already been done. It can take up to 3 weeks from infection before actual signs appear. As with most conditions prevention is the key.

Diagnosis is based on the clinical history on the farms, signs shown by the calves and examination of faeces for oocysts. Early in the infection, oocysts may not yet have appeared in faecal samples so sometimes a repeat test may be necessary to confirm the diagnosis.


There are no vaccines to prevent coccidiosis and prevention is based on good calf management, nutrition, hygiene and minimising stress. Prevention of the disease and clinical signs can be achieved by treatment with Baycox (toltrazuril) about 1 week before outbreaks are historically expected on a particular farm. Often coccidiosis occurs soon after changes to diet or housing or mixing of calves from different sources. A treatment 1 week prior to these times will help prevent disease. If one calf in a group is showing signs, it should be assumed the other calves have been exposed and should be treated too.


Baycox contains 50mg/mL toltrazuril, a potent coccidiocide. Unlike some feed additives such as coccidiostats which suppress infection, Baycox kills each developmental stage of this organism. If given before signs are seen but are historically expected, coccidiosis related diarrhoea can be prevented and further contamination of the environment with oocysts is reduced. At the same time, the ability of the calves to develop their own immunity is not affected.

Economic benefits of treatment

Apart from better calf health, better survivability and less oocyst shedding resulting in lower environmental contamination, preventing and treating coccidiosis has longer term economic benefits.

Baycox treated cattle have been shown to*:

  •  Have a lower age at first service
  •  Reached reproductive age sooner
  •  Have higher pregnancy rate

Baycox Product Profile

Active ingredient: toltrazuril 50mg/mL

Dosage: 3mL/10kg bodyweight

Withholding period: Meat; 56 days

*Influence of a metaphylactic treatment with Baycox® Bovis on the reproductive performances of Friesian heifers: a preliminary study. Veronesi et al. Parasitol. Res. (2013)