Pregnancy is associated with low fear reactions in ewes.

The aims of the study were: (1) to test the influence of pregnancy on responses of ewes to several fear-eliciting situations, (2) to compare the first and latest stages of pregnancy, and (3) to investigate possible correlations between fear reactions and progesterone levels. Fear reactions of nonpregnant (NP; N=22) and pregnant (P) Ile-de-France ewes (day 40 of pregnancy: N=43; day 140 of pregnancy: N=19) were compared during three situations classically reported to induce fear in sheep: isolation, surprise, and the presence of a human. P ewes displayed significantly lower fear reactions than NP ewes when isolated and when confronted with a surprise effect combined with the appearance of a novel object. This reduction in fearfulness may be mediated principally through reduced fear of isolation. However, fear of a human remained constant despite pregnancy. Fear reactions of ewes tested during isolation on gestation day 40 or 140 did not differ, suggesting that decreased fear is not restricted to the latest stage of pregnancy. A negative correlation was found between plasma progesterone levels and fear during isolation and surprise tests of ewes with low levels of progesterone. The decrease in fearfulness during pregnancy may have some adaptative value for the survival of the young.