Bleeding calf syndrome, or bovine neonatal pancytopaenia (BNP), is a condition in young calves characterised by extensive, unexplained haemorrhage and death, says Fiona Howie.
The disease was first identified in 2009 and was initially given the name bleeding calf syndrome, but this was changed to BNP by agreement of a pan-European group studying the condition, she says.
“Studies have shown the condition was caused by the use of a particular BVD vaccine, Pregsure, which has since been removed from the market.
“BNP has now been identified throughout the UK, in many countries in Europe and in New Zealand,” says Ms Howie.
The disease affects calves between seven and 28 days old, she says. “They may be fevered, appear to be suffering from pneumonia or bloody diarrhoea and be seen to bleed from the nose, gums or sites of ear-tags or injections.
“In other cases, however, the calves may be found dead having shown no sign of bleeding while alive. When these calves are examined post-mortem there is evidence of extensive internal bleeding.
“It’s now known the Pregsure vaccine caused some cows to produce antibodies against particular proteins on the surface of cells present in cattle with a different genetic make up to their own [like blood types in humans], as well as against BVD,” Ms Howie explains.
“Although the cow itself is unaffected because she does not express these proteins, her calf could be affected if it inherits enough of these proteins from the bull.”
The colostrum from the cows contain these rogue antibodies and depending on a number of factors, such as the genetics of the calf, amount of colostrum ingested and concentration of the antibodies, the antibodies can attack the calf’s cells, she says.
“The protein is expressed on a wide range of bovine cells, but is present in the highest quantities on the blood generating cells of the bone marrow, making them the main target.
“If enough cells are killed, this results in bleeding and a failure to fight infections followed by failure to replace the lost blood and death of the calf.”
As much as 5 per cent of the calf crop has died in some outbreaks, adds Ms Howie.
“There is strong evidence other calves on affected farms may suffer less severe bone marrow damage and manage to survive, but their ability to fight infection is suppressed.”
Despite withdrawal of the vaccine in 2010, numerous cases continue to be identified by SACCVS this year.
Many of these cases are from farms where BNP has not been identified in previous years and from cows known to have raised healthy calves every year since being vaccinated with Pregsure, says Ms Howie.
“At present there is no cure for BNP and it appears there will continue to be cases of it while cows historically vaccinated with Pregsure remain in the national herd.
“The condition can be controlled within individual herds by withholding the colostrum from any cows known to have been vaccinated with Pregsure for the first 24 hours of the calf’s life. Instead, calves should be fed colostrum which has been collected from younger cows, which did not receive the vaccine”
Analysis of blood samples can be used to investigate possible BNP involvement in live calves and provide a prognosis.
Ms Howie says: “Where clinical signs are seen in young calves which fit those described for BNP [including unexplained deaths] then producers are encouraged to submit the calf to SACCVS or the Animal Health and Veterinary Laboratories Agency for post-mortem examination.”
SACCVS receives financial support from the Scottish Government through the Veterinary and Advisory Services Programme.