Herd size linked to bovine TB risk

Intensive farming practices including larger herd sizes, maize growth, fewer hedgerows and silage use have been linked to higher risk of bovine TB (bTB), research from the University of Exeter has concluded. 

The survey, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and published in the Royal Society journal Biological Letters, analysed data from 503 farms which have suffered a TB breakdown alongside 808 control farms in areas of high TB risk.

It found that farms with herds of 150 cattle or more were 50% more likely to suffer a bovine TB outbreak than those with herds of 50 or fewer.

The research also revealed that patterns of crop production and feeding could increase the risks.

For every 10 hectares of maize, a crop that is a favourite food of badgers, which play a role in transmitting the disease, bTB risk increased by 20%.

The feeding of silage was linked with a doubling of the risk in both dairy and beef systems. Also, landscape features such as deciduous woodland, marshes and hedgerows were seen as contributory factors.

The research found that on farms with 50km of field boundaries, each extra 1km of hedgerow was linked with a 37% reduction in risk. It said this was likely because there was less contamination of pastures by badger faeces and urine in hedgerow-rich areas.

Marshland was associated with increased risk, possibly as a secondary effect of infection with liver fluke – a disease linked with wet environments and which interferes with the diagnosis of bTB in cattle, the research concluded.

“In the worst-hit areas, farms are frequently affected over and over again with crippling consequences. If lower intensity production means better animal health, it offers a sustainable long-term strategy in high-risk areas,” said Dr Fiona Mathews, associate professor in Mammalian Biology, who led the study.

“We have now shown that wider environmental management is also important. By finding out more about these links, we hope that we can help eradicate this terrible disease.”

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