NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare.

Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

CCN

(Cerebrocortical necrosis, Polioencephalomalacia)

The NADIS data show that several outbreaks of this disease has been seen in recent months

What is CCN?

CCN is a brain disease, seen in cattle and other ruminants. It mostly affects weaned calves or youngstock on feedlots (with 6 to 18 months being the most common age). Although common it’s usually seen only in one or two animals at a time. Outbreaks with large numbers of affected animals can occur, but even in these cases the proportion of affected animals remains low. For example, in a recent outbreak in a group of 50 pedigree Charolais heifers only 5 animals were affected.

The cause of CCN is not fully understood but there is a very strong link to deficiency of vitamin B₁ (thiamine). The bacteria in the rumen normally create this vitamin, so cattle do not normally need it in feed. However, if there are thiaminases (enzymes that break down B₁) in the rumen, then the animal can become deficient. These enzymes can come from the food (e.g. bracken), but more commonly they are produced by rumen bacteria. These are normally present in the rumen at low levels, but in some situations they multiply greatly and produce enough thiaminase to cause deficiency of B₁. Some outbreaks of CCN have been associated with sulphur toxicity, but even in these cases, B₁deficiency may be involved.

Clinical Signs

§ Sudden onset in an apparently normal calf

§ Depression

§ Blindness

§ Muscle tremors, particularly head and neck

§ Head pressing, neck twisting and flicking eyes

§ Disease progresses to convulsions, collapse, and death

Diagnosis

· Clinical signs are helpful, but can mimic other disease so get veterinary advice as soon as possible .

· Response to treatment is almost diagnostic in itself

· Post-mortem examination of the brain is the only practical method of confirming CCN

Treatment

· High doses of vitamin B₁ given intravenously, with follow-up injections

· The earlier treatment is given the more effective it is. However, even with early treatment the death rate can be 25%

· Supplementation of apparently non-affected animals may be beneficial

Prevention

As a sporadic disease CCN is difficult to prevent. Minimising rapid dietary changes may prevent the bacterial flora change that leads to increased thiaminases

Richard Laven PhD BVetMed MRCVS