Scientists detect Johne's-linked antibodies in newborn calves

Blood samples already taken from newborn calves could offer researchers a new way to investigate early-life exposure to Johne’s disease.

Scientists at the Royal Veterinary College found that antibodies linked to the disease could be detected in calves after they had received colostrum from their mothers.

However, the researchers stressed that the measurements cannot diagnose Johne’s disease or prove that a newborn calf has been infected.

Instead, the findings may help scientists study when calves are most at risk and support future improvements in herd surveillance.

The study involved 38 newborn dairy calves and their mothers at a commercial farm in south-west England.

The blood samples had originally been collected to check whether the calves had successfully absorbed antibodies from colostrum.

Researchers then used the remaining serum to measure antibodies associated with Mycobacterium avium subspecies paratuberculosis, known as MAP, which causes Johne’s disease.

Calves born to cows with detectable MAP antibodies had higher levels of MAP-specific antibodies than calves whose mothers did not.

The results were consistent with antibodies being transferred from cow to calf through colostrum.

Researchers also found that the relationship between antibody levels and colostrum absorption differed depending on whether the mother tested positive or negative for MAP antibodies.

Johne’s disease is a chronic and incurable infection affecting cattle.

Animals are thought to become infected during the first weeks or months of life, but symptoms may not appear for several years.

The disease damages the lining of the small intestine and can cause severe weight loss, reduced milk yields, diarrhoea and death.

More than half of UK dairy herds are estimated to be affected, creating significant animal welfare and economic concerns.

Most current surveillance programmes focus on adult cattle, leaving uncertainty over how exposure occurs during early life.

Jonathan Hedgecock, an RVC veterinary graduate and lead author of the study, said further research into new testing methods was needed.

He said: “Many calves are already blood sampled for serum total protein at a young age, so being able to test calves at this age would be straightforward as we wouldn’t need to take additional blood samples nor would we have to wait until they develop disease as adults.”

Dr Steven Van Winden, associate professor of population medicine at the RVC and supervisor of the research, said the long delay between infection and visible disease made Johne’s difficult to investigate.

He said: “Johne's disease is unusual because infection typically occurs very early in life, yet we often cannot detect its consequences until years later.”

“Our study shows that antibodies against the disease can be transferred from cow to calf and measured in newborn calves.”

He added: “While much more work is needed, this opens up an intriguing possibility for studying exposure risk during one of the most important periods in a calf's life.”

The researchers said the findings could eventually support further work on herd surveillance and early-life risk assessment, but additional studies will be needed before the approach can be used more widely.