Evaluating the effect of semi-group housing of rabbit does on their offspring's fearfulness: can we use the open-field test?

Breeding does are usually housed one doe per cage, but there is an increased interest in (semi-)group housing systems designed to improve welfare. However, there is a lack of information on how such systems actually affect different aspects of rabbit welfare. We aimed to discern differences in fearfulness in female offspring born and raised in conventional single-doe housing (1 doe + litter/cage) and in semi-group housing (1 doe + litter/cage until the litter was 18 days old, 4 does + 4 litters/pen thereafter). To this goal, we used the most commonly used test to assess fearfulness in rabbits: the open-field test. The classic interpretation of this test is that increased locomotion indicates decreased fearfulness. However, other underlying motivations for open-field locomotion have been proposed for other species (e.g. exploration and sociality). The underlying motivation is of great importance to interpret test results in terms of welfare. Therefore, the second aim of this study was to determine if fearfulness was the most likely cause of differences in rabbits' open-field behaviour, by assessing its development over time, repeatability and relationship to other behavioural tests (novel object test, social runway test). Rabbits born in the semi-group environment travelled less distance (p = 0.03) and were slower to leave the start corner during the open-field test (p = 0.001). They reared less during a novel object test (p = 0.03), but were not significantly slower to approach the object than offspring from the single-doe environment, and did not behave differently during a social runway test (p > 0.10). Although differences in open-field locomotion were found, the decrease in locomotion over consecutive test sessions contradicts that this behaviour is (exclusively) mediated by fearfulness in the rabbit. Exploratory motivation seems a more accurate interpretation. This greatly limits the usefulness of open-field locomotion as a welfare indicator in this species.