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Introduction
Coccidiosis is one of the most common and important parasitic diseases of cattle worldwide ( Daugschies and Najdrowski 2005 ). The Eimeria parasites that cause coccidiosis are commonly seen where cattle are raised under intensive conditions. Bovine coccidosis is primarily a disease of young calves, normally occurring between three weeks and six months of age ( Taylor and Catchpole 1994 ). All age groups of cattle are susceptible to infection, but clinical disease is most common in young calves reared under intensive husbandry conditions and more common in housed animals than those on pasture (Taylor and Bartram 2012). Eimeria infection causes diarrhoea leading to reduced weight gain and economic losses ( Fitzgerald 1980 , Gräfner and others 1985 ).
Of the 21 Eimeria species that have been reported in cattle ( Daugschies and Najdrowski 2005 ), 13 species are commonly reported in cattle, of which two species (E. zuernii and E. bovis ) are considered highly pathogenic ( Taylor and others 2007 ). Clinical signs of haemorrhagic diarrhoea are associated with the presence of these two species, which occur in the lower small intestine, caecum and colon ( Ernst and Benz 1986 , Taylor and Catchpole 1994 , Taylor 2000 ). In addition, a third species, Eimeria alabamensis , has been reported to cause enteritis in first-season grazing calves in the first week following turnout in some European countries ( Gräfner and others 1985 , Svensson and others, 1994 ).
Outbreaks of clinical coccidiosis are usually associated with a previously stressful situation such as change of environment, overcrowding or feed changes. These outbreaks can appear suddenly and may prove troublesome to resolve as they often occur in intensive farming systems, particularly where good husbandry and management are lacking ( Taylor 2000 ). Coccidiosis is often diagnosed by faecal examination in order to detect oocysts and it is generally recommended that the pathogenic species are identified as present, rather than simply counting oocyst numbers ( Jolley and Bardsley 2006 ), as there is no strong correlation between the numbers of oocysts shed and severity of clinical signs ( Daugschies and others 2007 ), although a threshold of 500 oocysts per gram of faeces (OPG) of pathogenic Eimeria species has been suggested as relevant...