Shared use of mineral supplement in extensive farming and its potential
for infection transmission at the wildlife-livestock interface
Abstract
Recently, the survival of Mycobacterium bovis on livestock mineral
blocks has been confirmed, but little is known about its implication in
the transmission of animal tuberculosis (TB) under field conditions. The
objective of this study was to describe the shared use of mineral
supplements in four extensive beef cattle farms from a high TB
prevalence area in South Central Spain, to identify the main factors
explaining their use, and characterize its potential role for the
transmission of Mycobacterium tuberculosis complex (MTC). This is
relevant to design control measures at the wildlife-livestock interface.
Animal activity was monitored by camera-trapping at 12 mineral
supplementation points during spring and fall. Additionally, swabs were
periodically taken from the mineral substrates and analyzed by PCR
searching for MTC DNA. Cattle, pig, goat, sheep, wild boar and red deer
were all recorded licking on mineral supplementation points. Livestock
species were the main users and presented a diurnal use pattern. Wild
ungulates presented a nocturnal-crepuscular use pattern, with scarce
overlapping with livestock. Wild boar presence was positively related to
cattle presence at mineral supplementation points, whereas red deer
presence was higher in supplemental points closer to forested areas,
mostly in absence of cattle. We recorded 266 indirect wildlife-livestock
interactions (i.e. two consecutive visits that occurred within 78h), all
of them derived from 21 unique wildlife visits. All the analyzed swabs
resulted negative to MTC DNA. Comparing to other environmental sources
of MTC in our study area, mainly water ponds, this research evidenced
that mineral blocks are less attractive to wildlife. However, the
potential for interspecific transmission of MTC or other pathogens
cannot be discarded. The risk for interaction at mineral supplementation
points and further transmission can be prevented by implementing
specific measures in the context of integral biosecurity plans at the
wildlife-livestock interface, which are proposed.