Coccidiosis in young calves is caused by infection by protozoan
parasites called Eimeria spp. which parasitize the lining
of the alimentary tract causing diarrhoea. E. zuernii, E.
bovis and E. alabamensis are the most common and
pathogenic. Infection causes a loss of absorptive capacity of
the gut with consequent diarrhoea and possibly dysentery.
Outbreaks of disease are commonly seen 3-4 weeks after mixing
groups of recently-weaned dairy calves. Disease outbreaks occur in
young dairy calves associated with overstocking and contaminated
accommodation. Contaminated watercourses are a major risk of
coccidiosis for young spring-born beef calves while at pasture
during the summer.
Fig 1: Outbreaks
of coccidiosis can occur in calves associated
with contaminated surface water (note the midden in the
Contaminated surface water is a risk for coccidiosis,
paratuberculosis, leptospirosis and salmonellosis. This area must
be fenced off and mains water supplied where available.
In severe clinical coccidiosis there is sudden onset of profuse
foetid diarrhoea containing mucus and flecks of fresh blood with
staining of the perineum and tail. Straining with partial
eversion of the rectum may occur in severe cases. Affected animals
do not have an elevated rectal temperature but their appetite is
greatly reduced and they develop a gaunt appearance.
Coccidiosis in a group of beef calves showing sudden onset of
profuse foetid diarrhoea containing mucus and flecks of fresh blood
with staining of the perineum and tail. This outbreak
occurred during hot summer weather which caused the stream
supplying water to this field to dry up to pools of contaminated
Straining with passage of only mucus. Partial eversion of
the rectum may occur in severe cases.
More usually, chronic wasting and poor appetite are the
presenting signs. Morbidity is high but mortality, even in
severe cases, is low. Convalescence is protracted in all
cases causing financial losses due to poor weight gains.
Early weight loss in beef calves with diarrhoea caused by
Your veterinary surgeon will also consider:
Many calves affected - parasitic gastroenteritis such as type I
ostertagiosis when at pasture during late summer, and
If only one calf is affected - intussusception, abomasal
ulceration, persistent infection with BVDV, necrotic enteritis,
ragwort poisoning, peritonitis will be considered by the veterinary
Veterinary diagnosis is based upon typical clinical findings
affecting a large number of calves in the group.
Interpretation of faecal samples is not simple because there are
low numbers of oocysts present in the faeces of many normal
calves. The stage of infestation also greatly influences the
number of oocysts present in faeces. The demonstration of large
numbers oocysts in faecal samples is helpful but speciation to
determine whether these coccidia are pathogenic (capable of causing
disease) is expensive and rarely undertaken in field
outbreaks. There is a good response to specific
Histopathology findings of coccidiosis in the gut of a dead calf
confirms the clinical diagnosis.
It is very important to move calves from infected
pastures/premises immediately. Toltrazuril and diclazuril can be
used for both treatment and prophylaxis of coccidiosis. Oral fluid
therapy may be indicated in certain cases. Your veterinary surgeon
should be consulted on the best therapy in your situation.
Strict attention to disinfection of buildings between batches of
calves and clean feeding areas mean that coccidiosis is uncommon in
modern clean dairy units.
Decoquinate can be used in-feed for prevention of coccidiosis in
Disease in beef calves may result from contaminated water
courses in pastured cattle during summer months where there is no
other water supply. Fence off all surface water wherever possible
and supply piped water to water troughs.
As survival of oocysts is possible from one year to another -
calving on the same pasture each year may increase the risk of
Weight loss and protracted convalescence may result in lower
weaning weights in beef calves. Gathering calves for
treatment, plus medicines, also adds to the costs of disease.
Fig 6: Poor
growth/condition loss following coccidiosis.