Infection with Eimeria is one of the most economically important diseases of sheep. Historically, some Eimeria spp
were thought to be infectious and transmissible between sheep and
goats, but the parasites are now considered host-specific. The names of
some species of goat coccidia are still erroneously applied to species
of similar appearance found in sheep. E crandallis and E ovinoidalis (ninakohlyakimovae) are pathogens of lambs, usually 1–6 month old; E ovina appears to be somewhat less pathogenic. Older sheep serve as sources of infection for the young. All other Eimeria of sheep are essentially nonpathogenic, even when large numbers of oocysts are present in feces.
Signs include
- diarrhea (sometimes containing blood or
mucus),
- dehydration,
- fever,
- inappetence,
- weight loss,
- anemia,
- wool
breaking, and death.
- The ileum, cecum, and upper colon are usually most
affected and may be thickened, edematous, and inflamed; sometimes, there
is mucosal hemorrhage.
- Thick, white, opaque patches containing large
numbers of E ovina oocysts may
develop in the small intestine. Because oocysts are prevalent in feces
of sheep of all ages, coccidiosis cannot be diagnosed based solely on
finding oocysts. Peak oocyst counts of >100,000/g of feces have been
reported in 8- to 12-wk-old lambs that appeared healthy. However,
diarrhea with oocyst counts of a pathogenic species of >20,000/g is
characteristic of coccidiosis in sheep. Immune complex
glomerulonephritis has also been attributed to coccidiosis. Fly strike
and secondary bacterial enteric infections may accompany coccidiosis in
lambs.
Lambs 1–6 month old in lambing pens, intensive grazing
areas, and feedlots are at greatest risk as a result of shipping, ration
change, crowding stress, severe weather, and contamination of the
environment with oocysts from ewes or other lambs. Because occurrence of
coccidiosis under these management systems often becomes so
predictable, coccidiostats should be administered prophylactically for
28 consecutive days beginning a few days after lambs are introduced into
the environment. A concentrated ration containing monensin at 15
g/tonne can be fed to ewes from 4 wk before lambing until weaning, and
to lambs from 4–20 wk of age. The toxic level of monensin for lambs is 4
mg/kg. Lasalocid (15–70 mg/head/day, depending on body wt) may be
effective. A combination of monensin and lasalocid at 22 and 100 mg/kg
of diet, respectively, is an effective prophylactic against naturally
occurring coccidiosis in early weaned lambs under feedlot conditions.
Treatment of affected sheep once coccidiosis has been
diagnosed is not effective, but severity can be reduced if treatment is
begun early. A single treatment of toltrazuril (20 mg/kg) can
significantly reduce the oocyst output in naturally infected lambs for
~3 wk after administration. Diclazuril (1 mg/kg) is an effective oral
anticoccidial in lambs and is administered once at about 6–8 wk of age
(most common) or (twice at 3–4 wk of age and again 3 wk later).
Sulfaquinoxaline in drinking water at 0.015% concentration for 3–5 days
may be used for treatment of affected lambs. In groups of lambs at
pasture, the frequent rotation of pastures for parasite control will
also help control coccidial infection. However, when lambs are exposed
to infection early in life as a result of infection from the ewe and a
contaminated lambing ground, a solid immunity usually develops and
problems are seen only when the stocking density is extremely high.