Bleeding Calf Syndrome

So called “Bleeding calf syndrome”, Bovine neonatal pancytopaenia (BNP) is an emerging disease in Scotland and other parts of the UK, having been first noted in mainland Europe in 2006/7. The dramatic clinical signs, occurring almost exclusively in calves of less than 21 days old are of widespread internal and/or external haemorrhage.

Common sites of bleeding are from the nose, from small wounds, such as ear tagging or injection sites, and into the intestine, causing blood in the faeces. Not all affected calves show signs of external bleeding; some may be found dead. In the UK, researchers from Moredun, SAC, VLA and the Royal (Dick) School of Veterinary Studies have been working together to try to establish the reason for the sudden emergence of the disease and its cause.

The explanation for the bleeding is that there are too few platelets in the blood (this is scientifically known as thrombocytopaenia). Platelets are vital to stop bleeding and when there are too few, haemorrhage results. What has become apparent is that the low platelet count is due to bone marrow failure at an early age. Bone marrow failure means that new platelets, as well as red and white blood cells, are not produced. Because platelets are among the shortest lived of the blood components produced by bone marrow, thrombocytopaenia and bleeding is an early sign of bone marrow failure. However, as the disease affects all the cells in the bone marrow, including the white cells important for fighting infections, some calves also have infections.

The disease is fatal in the large majority of calves when bleeding is noted – only a handful of animals survive. It is currently thought that there may be other sub-clinically affected calves which do not bleed. It is presumed that these animals have a less severe bone marrow suppression and thus a smaller drop in platelets. While there are other conditions of calves which are known to cause bone marrow failure, including bracken poisoning, toxins and diseases such as BVDV, these causes have not been associated with these new cases.

The focus of research into Bleeding calf syndrome in the UK has been on three areas;

• Determination of the risk factors for developing disease, using a questionnaire completed by farms which have had cases; this is currently being analysed.
• Study of tissues from affected animals to define the bone marrow changes seen in cases and rule out known causes.
• Looking for an infectious agent.

Moredun scientists have been working as part of the UK group, specifically on the search for a virus infection. More than 50 cases have been tested by virus isolation and by other testing methods but we have been as yet unable to find any evidence of virus infections.

At this time it is not certain whether the disease starts before or after the calves are born and this will be an important area of future study.