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Abstract
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 control rabbit from the same farm on the same day. Serum samples were collected immediately after shooting. The serum samples were tested for RHD titres from 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 serological 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 loss of the outer pinna from about 0.5–2.0 cm above the intertragic notch. Histological changes in affected ears consisted mostly of focal mineralisation in the auricular cartilage, proliferation of cartilaginous tissue and loss of cartilage. The serological findings showed a significant association between 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 distortion of the pinna, withering and loss of the outer pinna. The serological findings suggests that RHD is a likely factor in the development of the ear lesions.