The latest perspectives on coccidiosis in calves, its diagnosis and control, impact on animal performance and its link to chronic peri-weaning scours, were presented at a technical symposium held by Bayer Animal Health in Killarney, Ireland, in November, and by Dr Tony Andrews at the BCVA congress which followed.
At the Bayer technical symposium, Dr Abdülkerim Deniz, from Bayer Animal Health in Germany, explained that of the 13 species of the protozoan Eimeria, there were three pathogenic species: E. bovis and E. zuernii in housed situations, and at pasture E. alabamensis.
The most common species found in the UK are E. bovis and E. zuernii. These differ in appearance under the microscope and in their prepatent periods (the time from uptake of oocysts to excretion), which are 17-22 days and 15-19 days respectively.
The effects of coccidiosis are hard to quantify. Most calves could be carrying sub-clinical levels of infection, and despite the lack of any outward signs of disease will suffer depressed feed intakes and compromised growth and future performance.
When the disease reaches clinical levels, diarrhoea results – this can start before oocysts are shed, and is likely to be watery where E. zuernii is the cause, whilst haemorrhagic diarrhoea is typically seen in E. bovis cases.
Coccidial oocysts can survive temperatures as low as -8deg. C for up to five months and have even been known to survive winter on Norwegian pastures. Currently no disinfectant is 100% effective against them.
So the establishment of metaphylactic methods of control, along with good hygiene and management, are essential to prevent clinical disease outbreaks and to limit intestinal damage and subsequent reduced animal performance.
Optimum treatment timing
For housed calves, the onset of diarrhoea is likely to occur after re-grouping – as animals pick up oocysts from previous calves. However, the best time to take preventive action with a coccidiocide such as Baycox Bovis will vary from farm to farm for two reasons: firstly, the prepatent periods of the two pathogenic strains differ; and secondly, it depends on the housing and management of the calves as to when they will encounter stress and environmental disease challenge.
To determine appropriate timing for treatment, Dr Deniz recommended taking faecal samples for oocyst detection two weeks after relocating calves from individual pens to group pens, and then again one week later, and assessing oocyst levels. He recommended metaphylactic treatment to be initiated one week prior to the peak of oocyst excretion.
Faecal speciations to identify if pathogenic strains are present on a unit are available from Bayer Animal Health. Keith Cutler, from the Endell Veterinary Practice, presented his experiences of coccidiosis in general cattle practice. The text book signs of coccidiosis – tenesmus and bloody faeces – were rarely seen.
He did, however, find a lot of periweaning scour in dairy-bred calves – this manifested as chronic pasty faeces in calves of three to 10 weeks of age, which persisted for several weeks. Faecal coccidial oocyst counts would be low and so farmers usually blamed the scour on too much cake. However, in many of these cases, coccidial infection could be to blame.
At the BCVA congress itself, Dr Tony Andrews presented his findings on why the prevalence of coccidiosis significantly increased in the 1990s and still remained at high levels today.
He referred to VLA data which showed a sharp rise in the incidence of clinical coccidiosis cases in the 1990s, peaking to 706 samples in 1997 and remaining at similar levels for the past decade. However, prior to 1992 there had been less than 250 cases per year.
He said this may have been due to the fact that antibiotic growth promoters used to be included in cattle rations; ahead of legislation banning their use, many feed companies began voluntarily taking them out of rations in the mid 1990s.
Another syndrome associated with coccidiosis is chronic peri-weaning diarrhoea. This typically manifests as morbidity of over 50% after weaning. This syndrome became prominent in the mid-1990s, the same time as the rise in coccidiosis cases.
Dr Andrews said that coccidial incidence is hard to discern as all cattle will have this at some stages of their lives. Cases of clinical disease are now more prevalent: in one large study of enteritis in unweaned calves, coccidiosis was the third most common cause of diarrhoea after cryptosporidiosis and coronavirus (Andrews, 2000). In another report it was the most common enteric problem in calves aged three to 12 weeks (Otter and Cranwell, 2007).
Signs of coccidiosis are typically seen in calves aged three weeks to six months, with a number of animals affected and low mortality. Some animals will exhibit soft or loose faeces, often with poor growth. Occasionally blood and tenesmus, and anaemia may be seen. Infected calves are likely to be more susceptible to other diseases.
Dr Andrews recommended taking five faecal samples for testing per 20 calves. It was also important to take from apparently healthy calves as well as those obviously affected – and to record which animals had clinical signs as well as those which did not.
Coccidial infection was “probable” if the faecal oocyst count was 5,000opg in one or more samples and there were physical signs in a group, or where the average count of 2,500opg was found in two or more calves. Where tests revealed one or more counts of over 2,500opg and mild signs, then this denoted “possible” coccidial infection.
The cost of coccidiosis
The production losses associated with coccidial infections in calves are hard to quantify since variables such as feed intake and feed conversion rates are not really known, plus almost all animals will at some time have sub-clinical levels of the disease.
Dr Andrews referred to research (Fitzgerald ,1972) in which calves infected with coccidiosis lost weight and did not regain it, being 22-27kg lighter than uninfected calves 10 months later.
Dr Andrews concluded that, as a rule of thumb, heavier heifers give more milk and for every 1kg of extra weight an extra four litres of milk in the first lactation was possible. Coccidial infection could ultimately cost between £25 and £60 per calf, not including remedial treatment costs.
Bayer’s Dr Deniz had quoted Swedish research (Svenson and Hultgren, 2008) which showed that in 105 Swedish dairy herds (a total of 1,562 cows), animals which had shown mild diarrhoea before 91 days of age gave an average 344kg less milk in their first lactation.
Andrews, A. H. (2000) Calf enteritis – New information from NADIS. 5 (1): 30-34. Fitzgerald, P. R. (1972) The economics of bovine coccidiosis. Feedstuffs 4th September, 44: 28-30 Otter, A. and Cranwell, M. (2007) Differential diagnosis of diarrhoea in adult cattle. In Practice 29 January 2008, pp9-19. Svensson, C. and Hultgren, J. (2008) Associations between housing, management and morbidity during rearing and subsequent first-lactation milk production of dairy cows in south-west Sweden. J. Dairy Sci. 91: 1,510- 1,518.