Blindness, CCN and PEM

CCN (Cerebrocortico necrosis) in calves, or PEM (Polioencephalomalacia) in Sheep

CCN is a condition affecting growing cattle (up to 18 months typically) and sheep of all ages, tending to occur in outbreaks and is associated with high concentrate rations, Low roughage diets, including lush grass which is high in sugars but low in structural fibre which is associated with Sub-Acute Ruminal Acidosis and acute Acidosis. The condition has been associated with well-nourished calves that have been left hungry or find themselves on a poorer plane of nutrition suddenly.

The cause of CCN is not fully understood but there is a very strong link to deficiency of vitamin B1 (thiamine). Thiamine is critical for the brain at a cellular level and also for water and electrolyte balance of the animal and a deficiency can lead to lactate accumulation in the muscle tissues

The  bacteria  in  the  rumen  normally create this vitamin, so cattle do not normally need it in feed. Young and growing animals do not always have a fully functioning rumen and so cannot properly synthesise B vitamins leaving a requirement for supplementary B Vitamins in the diet.  Alongside actual deficiency, if there are thiaminases in the rumen, then the animal can become deficient. Thiaminases actively break down Vitamin B1 and certain enzymes actually inhibit Vitamin B1 from being absorbed from the bloodstream. These enzymes can come from   the   food, some species of fern and bracken also contain the thiaminase enzyme as a natural insect repellent, but more  commonly they are produced by rumen bacteria.

These bacteria are normally present in the rumen at low levels, but in some situations, especially where the pH in the rumen is lowered (SARA / Acidosis) they multiply greatly and produce enough thiaminase to cause deficiency of B1. The presence of excessive levels of Sulphur in the diet can have an inhibitory effect so care must be paid to water sources which contain high Sulphur levels and also the spreading of certain fertilisers which are high in Sulphur

Identifying suspected cases

Affected  animals  are  dull  and  may  isolate themselves from others in the group.  There is high head  carriage  and  affected  cattle  may  stagger. There is blindness but animals react abnormally to sudden touch and loud noises. As the disease progresses, animals often head press into corners and there is frequent teeth grinding.  Seizure activity is common during the later stages if untreated. Ultimately this condition, if left untreated, will lead to death.