Sex differences in fear reactions in sheep

Abstract

In order to assess potential sex differences in fear reactions, 40 rams and 40 ewes were studied using a battery of tests previously designed and validated. Animals were individually confronted with situations classically reported to induce fear in sheep: i.e. isolation from conspecifics, surprise effect and presence of a human. Eight groups were studied, each comprising ten animals of the same sex, breed (Romanov or Ile de-France) and rearing condition (artificially or dam-reared). Males and females of the same breed and rearing condition were tested alternately during the same week (4 days of habituation plus 3 days of tests) in order to prevent fear reactions from being biased by differences in the environment (such as noises, ambient light, etc.) which could influence fear reactions. Twenty-six behavioural items related to fear were recorded. Furthermore, an overall score, based upon those items and reflecting the fear level of each subject in each of the test situations, was calculated. All the significant differences between sexes ( P < 0.05) consistently indicate that rams are less fearful than ewes. Their overall scores were respectively, 37.0 ± 10.5 vs. 44.0 ± 11.9 ( P < 0.01) in the isolation test, 36.1 ± 11.0 vs. 44.9 ± 8.4 ( P < 0.001) in the surprise test, 38.5 ± 12.5 vs. 42.5 ± 13.6 ( P = 0.06) in the human test (higher scores reflect heighthened fearfulness). When subjected to non-social fear-eliciting situations, rams were seen to be less fearful than ewes. This conclusion could serve as an impetus for more general behavioural studies of factors influencing fearfulness and thus adaptability of farm animals to intensive housing conditions.