Morphometrical observations on the mandible of five strains of rabbits and strain identification using mandible measurements

In order to clarify the relationships between five strains of rabbits and to identify the strains, principal component and discriminant analyses were carried out using 12 mandibular measurements of three inbred strains (JW-NIBS/Y (JW/Y), NW-NIBS/Y (NW/Y) and Dutch-NIBS/Y (D/Y)) and two outbred strains (JW-NIBS (JW) and NW-NIBS (NW] which were maintained at the Nippon Institute for Biological Science. The results obtained were as follows. (1) Principal component analysis revealed that in the males the mandible of JW was the largest but with considerable variation. D/Y was the smallest of all strains examined. The mandibles of NW and NW/Y were similar to the JW mandibles but had a shape which was shorter and higher. In the females the mandible of NW was the largest of all strains and, as in the males, D/Y was the smallest and JW varied markedly. (2) Discriminant analysis showed the probability of erroneous discrimination to be 14.8% (34/229) when the inbred and outbred strains were combined. In both sexes erroneous discrimination mostly occurred between NW and NW/Y, which have the same origin, and between JW and NW, which have a common ancestor. However, when the inbreds and outbreds were identified separately by discriminant analysis, the probability of erroneous discrimination was low in both cases (4.5% (5/112) and 7.7% (9/117) respectively). These results indicate that strain differences are found in the size and shape of rabbit mandibles and that mandible analysis is effective for strain identification of laboratory rabbits.