Coccidiosis in Lambs
· There are 15 types of coccidian that may affect sheep. Only two are recognised to causing this disease in the UK; Eimeria ovinoidalis and Eimeria crandallis.
· Lambs take in coccidian oocysts (eggs) by oral route. Inside the gut the oocysts hatch, invade the gut cells and multiply dramatically. This leads to damage to the inside lining of the gut; as coccidia emerge by bursting cells and this also dramatically increases the amount of oocysts shed in the lambs faeces. The amount of oocysts shed can be as much as million-times more than were ingested.
· Damage to the cells lining the ileum, caecum and colon results in diarrhoea which may contain mucus or blood. This may be accompanied by straining, pain, weight loss and possibly death of the lamb. Even animals that don’t show clinical signs may show poor weight gain as the gut has a reduced ability to absorb nutrients from food.
· Source of oocysts: low numbers of oocysts are shed by some ewes and oocysts from previous season lambs will survive overwinter. Lambs will then multiply these numbers dramatically.
· Most often seen in lambs aged 4-8 weeks, not common over 3 months old.
· Lambs are able to mount a good immune response to coccidian so there is a lower risk if lambs are exposed to low levels earlier in life. However, this low level exposition will contribute to environment infestation of coccidian. Clinical disease is seen when young lambs are exposed to large amounts of coccidian. Such situations include when: young lambs are moved to pastures previously grazed by older lambs; lambs kept in extended clean conditions after birth are turned out onto contaminated pasture. Immunity to one type of coccidia is not universal.
· Nematodirus is another common cause of diarrhoea and death in 6-12 week old lambs at grass and may occur alongside coccidiosis.
· Treatment: during an outbreak, immediately either diclazuril or toltrazuril should be given to all lambs over 3 weeks old. During an expected outbreak, when lambs are turned out, 10-14 days after this date, lambs should be treated with diclazuril. (as diclazuril has no residual activity). However toltrazuril has a longer duration; so only one dose is necessary. Ideal timing is 7 days after turn out, or before expected outbreak. Tzuril has shown to be more effective than Dzuril.