Study examines link between red deer and cattle TB on Exmoor

Peer-reviewed preliminary research suggests groups of wild deer roaming on Exmoor may be linked to outbreaks of TB in local cattle herds.

Retired medical scientist Keith J Collard used lateral flow blood tests to look at the incidence of bovine TB in 106 wild red deer (Cervus elaphus) across Exmoor, ranging from less than one year to 10 years old. 

In total, 30 deer tested positive for TB (28.3%), of which stalked deer had a higher incidence (19 out of 55; 34.55%) than hunted deer (11 out of 51; 21.57%). 

See also: Charlie Flindt: We need to talk about deer numbers

Although the study only examined a small number of deer and areas in the UK, the results suggest TB could be more prevalent in wild red deer than previous studies had found, said Dr Collard, a former associate professor at the University of Plymouth and an expert in physiology.

He observed a “significant correlation” between the number of farms with TB reactors and the number of TB-positive deer in the regions. This indicated a “strong likelihood” of cross-species infection and supports previous studies that deer could be vectors for TB in cattle.

The National Trust-owned Holnicote Estate in the north-east of Exmoor National Park was the region with the highest incidence of cattle TB relative to the number of farms.

The trust banned deer hunting with hounds on their land in 1997 and its sole deer management strategy is stalking.

Dr Collard suggested the lack of disturbance due to hunting with hounds has had a “major effect” on the tendency for deer to congregate in high concentrations on the 5,026ha estate, which has contributed to the high level of TB in deer. This finding is supported by previous studies in Europe and New Zealand.

This theory could be tested scientifically with the reintroduction of hunting with hounds on the estate, he said.

Badgers are thought to be the main wildlife reservoir of TB, and farmers have raised cattle water troughs to stop them using them. 

Deer can still access these water troughs. However, Dr Collard says the most likely cause of infection between deer and cattle is shared grazing, either on farmland pasture or on the moor.

Oral vaccination

The study was published in the European Journal of Wildlife Research and it was funded by the Badgworthy Trust for the Preservation of Exmoor and the Badgworthy Land Company.

It concludes that a recently developed oral vaccination is the best method of limiting TB incidence in all host species. 

Blood samples were obtained from deer culled by the Devon and Somerset Staghounds, the Quantock Staghounds and from registered stalkers operating in the area.

All animals were culled as part of a deer management strategy on Exmoor and not specifically for this study. 

A Defra spokesperson said: “Wild deer are susceptible to TB infection, but in Great Britain they are generally considered to be spillover hosts – meaning they are unlikely to sustain the infection within their own population in the absence of infected cattle or a wildlife reservoir. There are usually only a few isolations of M bovis from wild deer each year.

“We continue to work with the farming community in Exmoor on this and are conducting a survey of TB in the wild deer population in the region.”