Gavin

Virtually 100% of young cattle (under 2 years of age) in NZ will show the presence of Coccidia in the faeces.

But first lets go back to the way they measure and report the presence of Coccidia.

The test is not a quantitative test i.e. the number of oocysts /gm of faeces but a qualitative one - looking for the oocysts in the faeces and roughly counting the number of oocysts per high powered field. The results are reported as

none seen - infection zero or very low

+              - infection very low and so should show no clinical signs

++            - Moderate infection with a significant number showing clinical signs

+++          - severely infected- scouring, straining, bloody faeces, loss of weight, death!!

The presence of some oocysts in the faeces is important in the development of some immunity to infection and so prevent the full blown disease. The severity of infection depends on the environmental challenge . These are mainly dirty wet bedding, puddles, swamps and drains contaminated with cow faeces . In Northland very high challenges are also seen in late summer early autumn after a period of rain and high humidity.

Concentrate feeding (pellets or meal) containing a coccidiostat will help to ensure that the Coccidia count stays at no more then the 1+ range . This obviously will only be achieved when concentrate intakes are greater then 0.5 kg/calf /day.  Calves bullied off the trough may be vulnerable so trough space is important. 

The typical clinical picture even in a severe challenge is where 20 % of calves will be severely ill and scouring dull etc.  After 5-6 days these calves will slowly recover (if treated) or die, then another wave of scours in another group will occur,  and so on.  So the answer to his question is that 20 -50 % will be showing clinical signs at any one time