Association of immune responses of Zebu and Holstein-Friesian cattle and
resistance to mycobacteria in a BCG challenge model.
Mycobacterium bovis is the main causative agent of bovine
tuberculosis (BTB) in cattle and it is also responsible for a proportion
of human TB cases. The annual cost of BTB worldwide is estimated at
US$3 billion. Zebu cattle are considered to be more resistant to some
infectious diseases than Holstein-Friesian (HF) cattle, including BTB.
However, epidemiological studies do not necessarily take into account
usage differences of the two types of cattle. It could be argued that HF
cattle suffer greater metabolic stress due to their mainly dairy use,
whereas Zebu cattle are mainly used for beef production. However, in
experiments comparing Zebu and European cattle, the number of animals
has been too small to draw statistically robust conclusions on the
differences in the level of resistance between these breeds of cattle.
Here, we used a recently developed vaccination-and-BCG challenge model
to compare the ability of naïve and vaccinated Zebu and HF cattle to
control/kill mycobacteria. Young male cattle of both breeds with similar
ages were housed in the same accommodation for the duration of the
experiment; after correcting for multiple comparison, we found that
there was a trend for vaccinated HF cattle to have lower cfu numbers
than non-vaccinated HF cattle (ρ = 0.057). No such trend was observed
between vaccinated and non-vaccinated Zebu cattle (ρ = 0.560);
similarly, no difference was observed between naïve HF and Zebu (ρ =
0.862) cattle. In contrast, evaluation of antigen-specific IFNγ
secretion indicated that Zebu and HF cattle differed in their response
to mycobacteria. Thus, under the conditions used in this work, the data
indicate that there are no differences between Zebu and HF cattle.
Further experiments, using larger numbers of animals may be required to
determine whether Zebu and HF cattle differ in their susceptibility to
infection with M. bovis.