Beware the threat of winter coccidiosis

Coccidiosis cases in autumn born calves housed over the winter are common and the disease risk remains high until Christmas.

Their immunity to the Eimeria parasite is variable and the relatively mild early winters of recent years has allowed coccidial oocysts to remain viable in the housed environment.

Dr Kat Baxter-Smith, livestock veterinary adviser with MSD Animal Health, said any passive immunity to coccidial oocysts gained from dam colostrum starts to wear off once the calves reach three weeks old.

“The majority of autumn born calves are beyond that age now so are particularly vulnerable over the next few weeks,” she said.

“However, while most older animals excrete some coccidial oocysts in their faeces most of the time, not all farms see clinical disease.

“The outcome of any infection in calves is a balance between the infection pressure from coccidial oocysts in the environment, calf immunity and stress factors such as overstocking, poor hygiene or adverse weather events.”

She said diarrhoea can be seen before the oocytes are shed in the faeces, adding: “Sampling more than one animal increases the chances of detecting a high oocyte count and helps with deciding the correct disease management plan.”

Good management of coccidia means helping calves to avoid disease and any growth setbacks while ensuring youngstock get enough exposure to the parasite to develop good immunity.

Dr Baxter-Smith said: “In ideal conditions, sound hygiene and management practices can control the level of oocyst challenge in the environment. But on most farms, strategic use of anticoccidial treatments will be required to manage the challenge and allow immunity to develop without loss of performance or disease.

“With most immune adults excreting only a few oocysts into the environment, it is infections in calves that result in very high levels of oocyst output. This causes heavy potential infectivity in the environment, leading to higher challenges and clinical disease in subsequent groups of youngstock.

“Anticoccidial treatments should therefore be targeted at youngstock; to allow exposure, but also to remove the parasite before there is any impact on productivity - and before further environmental contamination occurs.

“Timing of coccidiosis treatment is therefore crucial. You must treat after the calf is exposed, but before its gut is damaged.

This means detailed historical records of previous disease outbreaks are valuable, so always try to keep calves in age-related groups and treat all calves in those groups at the right time.”

Treatment options for youngstock include triazinone derivatives like the oral drench diclazuril. Calves with clinical signs of disease may also need other supportive treatment until the gut damage has had time to heal.

Dr Baxter-Smith added: “Oral drenches like Vecoxan® are generally the most convenient way of ensuring each calf receives the correct dose at the right time.”

Easy-to-administer as a single oral dose, Vecoxan® is a flexible coccidiosis management solution for calves of any weight, in any management system and

without any environmental restrictions or meat withdrawal period.

In addition, its strategic use with all young animals in a group allows natural immunity to develop with no need to dilute manure from treated animals before spreading¹.



  1. Van Leemput & Louineau. Diclazuril for coccidiosis in ruminants: safe for the environment? Poster at the 21st International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP), Ghent, Belgium. August 19-23, 2007.