Bleeding calf syndrome is an emerging disease in Scotland and other parts of the UK, which was first noted in mainland Europe in 2006-2007. It is almost always seen in calves of less than 21 days old, and is indicated by widespread internal and/or external hemorrhage. The common sites of bleeding are the nose; small wounds, such as ear tagging or injection sites; and from the intestine, where the symptom is blood in the feces. Not all affected calves show signs of external bleeding; some may simply be found dead.
The Moredun Research Institute (MRI) in Scotland is involved in collaborative work on the condition together with UK researchers from the Scottish Agricultural College, the Veterinary Laboratories Agency and the Royal (Dick) School of Veterinary Studies. The scientists have been working to try to establish the reason for the sudden emergence of the disease and also to identify its cause. There was also a meeting on the disease at the recent European Buiatrics Forum, open to scientists from all over Europe.
The bleeding appears to be linked to a low platelet count in the blood (thrombocytopenia), which disrupts the normal clotting mechanism designed to prevent hemorrhage. In turn, the low platelet numbers are caused by a bone marrow failure at an early age. This will affect all blood cell manufacture — although the shortage of platelets and bleeding will become obvious most quickly, affected animals short of white blood cells will find too hard to fight subsequent infections. It is not yet clear whether animals are born with the disease, or contract it after birth.
Work to date indicates that bleeding calf syndrome is fatal in the large majority of calves where bleeding is observed — only a minority of these animals survive. The scientists believe that there may be subclinical cases with no obvious bleeding, possibly involving a less severe bone marrow suppression and smaller drop in platelet numbers.
Bone marrow failure in calves is known to be caused by factors such as bracken poisoning, other toxins and diseases such as BVDV. However, no link has been established between these factors and the cases over the last two years.
The UK research effort into bleeding calf syndrome is concentrating on three areas: a determination of those risk factors associated with the disease, based on a questionnaire from those farmers with experience of the disease; the study of tissues from affected animals, in order to define the bone marrow changes seen in affected calves and to rule out known causes of failure and work to identify an infectious agent.
Moredun scientists have focused on the search for a virus infection, and have screened samples from more than 50 cases by virus isolation and other testing methods, but have as yet been unable to find any evidence of virus infections.
This information was excerpted with permission from the January 2010 Animal Pharm e-newsletter (www.animalpharm news.com) and written by Jamie Day.