final report - ARCHIVE: Defra

Management tools
7.4 Continued analysis of post-RBCT data
If recolonization of culled areas is slow, then the effects of proactive culling, as carried out in the RBCT, can
be expected to continue for some years. Indeed, the latest analysis of the RBCT data shows that the incidence
of bTB in cattle within proactively culled areas has now declined to a level substantially below that recorded
at the time of cessation of culling, while the ‘edge effect’ has disappeared (Jenkins et al., 2008a). It is essential
that provision continues to be made for periodic analysis of RBCT data relating to cattle bTB incidence in and
around proactively culled areas and within corresponding control areas, until such time as an equilibrium
situation is re-established (i.e. until there are no significant differences in herd breakdown rate between
proactively culled, surrounding and control regions). Only then will it be possible to compare the overall costs
and benefits of proactive culling.
7.5 Alternative culling regimes
So far, proactive culling has only been considered in the form of simultaneous removal, over a large area, of as
many badgers as possible. However, it is possible to envisage other forms of less-intensive culling that would
reduce badger populations more gradually and might, as a consequence, avoid major perturbation effects. The
aim of such culling would be to reduce badger population density to a level at which the disease is no longer
self-sustaining. We suggest that consideration be given to the modelling of alternative culling regimes, using
existing information about badger behaviour and population dynamics.
7.6 Fertility control
7.6.1 The Krebs Report gave brief consideration to the possibility of using fertility control as a way of reducing
badger population density and hence of controlling bTB in badgers (Krebs et al., 1997, p. 86). The
advantage of this approach is that it would be less detrimental than culling to badger welfare and
hence would be more publicly acceptable. Also, from the point of view of their reproductive biology,
badgers are in principle a good candidate for fertility control (Tuyttens & MacDonald, 1998). The use
of chemosterilants, delivered orally and aimed at female badgers, was considered by Krebs et al. to be
the most promising method of achieving fertility control. However, the risk of uptake by non-target
species, including cattle, was acknowledged to be a serious obstacle to this approach.
7.6.2 Since the Krebs Report, interest in agents of fertility control has switched towards immunocontraception,
which involves preventing reproduction by stimulating immune responses against gametes or
reproductive hormones. Immunocontraceptive agents should in principle be longer lasting, cheaper
and more species-specific than chemosterilants. However, despite considerable expenditure on the
development of immunocontraceptives, especially in the USA, France and Australia, some very basic
scientific, ecological and ethical issues remain to be resolved (e.g. Cooper & Larsen, 2006). In addition,
immunosterilization is being developed primarily in the context of control of pest species, not control
of disease. It could be inappropriate for the latter purpose because it would select against individuals
that have the best immune systems (Nettles, 1997) and might also interfere with disease diagnosis
(Tuyttens & MacDonald, 1998).
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