Cattle are more likely to contract bovine TB from the environment they live in than from direct contact with badgers, new research has revealed.
The study, by the Zoological School of London (ZSL) and Imperial College, used GPS tracking collars to follow badger and cattle over a two-year period on 20 farms in Cornwall, recording the extent to which the two species made direct contact.
“We know that badgers can give TB to cattle, and we have strong evidence that cattle can give TB to badgers, but we’ve never known how this transmission happens,” said Prof Rosie Woodroffe, senior researcher at ZSL. “That means it’s very difficult to give farmers specific advice on how to reduce the risk.”
The new study, published today (Friday) in Ecology Letters, reveals a high level of “contact opportunity”, with badgers showing a strong preference to roam on cattle pasture rather than any other land type.
“The reason for that is that badgers’ main food source is earthworms and earthworms are high density in cattle pasture and are quite accessible to badgers,” said Prof Woodroffe.
Despite this, the researchers found that the two species hardly ever met. Even though the research showed there were many times when both badgers and cattle were on the same range, not once in the equivalent of over 2,900 “cow nights”, did they come within 5m of each other. There was no direct contact.
If anything, the two species seemed to actively avoid each other, with the report showing badgers had a disproportionate preference for land over 50m away from cattle. “Badgers may love cattle pastures, but they hate cattle,” Prof Woodroffe concluded.
Despite this, Prof Woodroffe said there was strong evidence that both species were able to cross-infect each other with bovine TB, and the most likely route seemed to be through the environment.
“A TB-Infected badger is excreting Mycobacterium bovis in its faeces,” she said. “A small number of infected badgers have TB lesions in their kidneys so will be urinating TB, or if it’s in their sputum and they are snuffling about in the ground there is a potential for them to contaminate pasture, or drinking water.”
Cattle also excrete it in their dribble and dung, she added, “so it is likely that the transmission from cattle to badgers is also happening through the environment”.
The fact the bacteria can survive for long periods could explain why herds are often prone to reinfection with TB. “That has always been blamed on badgers, but you can’t assume that, having killed a badger, the problem is gone.”
Prof Woodroffe therefore suggested that farmers should focus more on the environment when it came to managing their cattle. “If a herd gets TB, the animals which test positive are kept in isolation, then slaughtered. But the pasture that they’ve grazed on and the slurry that they’ve contributed to is not treated as an infectious substance.”
In relation to the government’s badger culling policy, Prof Woodroffe said the observations from this study might explain why the benefits in terms of TB reduction only accrued slowly.
“We know that culling badgers changes the behaviour of the badgers that are still there after the cull,” she said.
Since those badgers are no longer defending territory, they no longer need to concentrate their urine and faeces in specific locations, potentially increasing contamination in cattle pasture.
“Our research certainly does not increase the case for badger culling,” she said. “Personally, I don’t think the case for badger culling is very strong anyway.”
But Catherine McLaughlin, NFU chief adviser on animal health and welfare, said culling was still a valid policy, as part of a multi-faceted approach.
“We have always said we must use all options available if we are to stand a chance of controlling and eradicating this devastating disease,” she said.
“This includes cattle testing, cattle movement controls and on-farm biosecurity. It also includes badger vaccination, once a vaccine is available again, and culling of badgers in areas where bovine TB is rife.”