Effectiveness of divergent selection for open-field activity in rabbits and correlated response for body weight and fertility.

Two lines deriving from the same rabbit stock were selected for 8 generations for high (H) or low (L) locomotor activity score in the open field (OFS). The divergent selection was most effective up to the 3rd generation in the H line and up to the 4th generation in the L line. In further generations a decrease of OFS in the H line and a "floor effect" (OFS = 0) in the L line were observed. The mean OFS increased significantly in consecutive trials in the H line, whereas this increase was non-significant in the L line. There was a negative and very high correlation between the latency to enter the open field and the OFS (-0.95 and -0.98 for the H and L line, respectively). The realized heritability of the OFS was 0.46 and 0.23 in generations 0-3 within the L and H line, respectively, and 0.44 and -0.06 in generations 0-8. As calculated on the basis of divergent selection, the heritability was 0.31 and 0.15 for generations 0-3 and 0-8, respectively. The L rabbits were heavier shortly before (4th wk, P < 0.001) and after (8th wk, P < 0.01) weaning, than those of the H line, whereas the H rabbits grew faster (P < 0.05) between the 4th and 20th wk of age. There was a tendency for decreasing weight gains in consecutive generations. Generally, a lower percentage of H females delivered litters than those of the L line, but this was due to a very low percentage of such females in the 3rd and 6th generations. It can be assumed that H and L lines represent different, i.e., active and passive, coping strategies. These lines of rabbits offer increased possibilities for physiologically and ethologically oriented studies, e.g., on the welfare of caged animals.