Aims. To investigate the relationship between loss of parts of the pinna in
rabbits and rabbit haemorrhagic disease (RHD).
Methods. A case-control study design was employed. Rabbits with ear lesions
were shot on farms in various locations in the South Island of New Zealand
. For each case, an attempt was made to obtain a sex- and size-matched cont
rol rabbit from the same farm on the same day. Serum samples were collected
immediately after shooting. The serum samples were tested for RHD titres f
rom 1:10 to 1:640. A selection of affected ears was examined histologically
. Odds ratios and their 95% confidence intervals were calculated to assess
the relationship between ear loss and RHD antibody status at various serolo
gical cut-off levels.
Results. Affected ears were characterised by firm cartilaginous nodules and
ridges, folding of the ear or loss of pinna to form a notch or complete lo
ss of the outer pinna from about 0.5-2.0 cm above the intertragic notch. Hi
stological changes in affected ears consisted mostly of focal mineralisatio
n in the auricular cartilage, proliferation of cartilaginous tissue and los
s of cartilage. The serological findings showed a significant association b
etween rabbits with ear lesions and elevated RHD titres.
Conclusion. The loss of the outer pinna in the rabbits under study was due
to degenerative and hyperplastic changes in the auricular cartilage with di
stortion of the pinna, withering and loss of the outer pinna. The serologic
al findings suggests that RHD is a likely factor in the development of the
ear lesions.