Pregnancy is associated with low fear reactions in ewes

The aims of the study were: (I) to test the influence of pregnancy on respo nses of ewes to several fear-eliciting situations,(2) to compare the first and latest stages of pregnancy, and (3) to investigate possible correlation s between fear reactions and progesterone levels. Fear reactions of nonpreg nant (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 clas sically reported to induce fear in sheep: isolation, surprise, and the pres ence of a human. P ewes displayed significantly lower fear reactions than N P ewes when isolated and when confronted with a surprise effect combined wi th the appearance of a novel object. This reduction in fearfulness may be m ediated principally through reduced fear of isolation. However, fear of a h uman remained constant despite pregnancy. Fear reactions of ewes tested dur ing isolation on gestation day 40 or 140 did not differ, suggesting that de creased fear is not restricted to the latest stage of pregnancy. A negative correlation was found between plasma progesterone levels and fear during i solation and surprise tests;of ewes with low levels of progesterone. The de crease in fearfulness during pregnancy may have some adaptative value for t he survival of the young. (C) 2001 Elsevier Science Inc. All rights reserve d.