Repeated transport and isolation during pregnancy in ewes: Differential effects on emotional reactivity and weight of their offspring

The aim of this experiment was to study the effects of different stressors applied to pregnant ewes during the last third of pregnancy on the emotional reactivity of their lambs. Forty ewes were subjected twice a week during the last 6 weeks of gestation to 10 sessions of isolation (ISOL, n = 20) or of transport in isolation (TRAN, n = 20). Nineteen other ewes (CON) were not disturbed. The emotional reactivity of their lambs to social isolation, a startling stimulus (opening of an umbrella), a novel arena and a novel object was tested at 1 and 3 months of age. Lambs born to ewes transported during pregnancy jumped less and explored more during tests involving exposure to isolation, novelty and startling compared to control lambs (p < 0.050). They stayed longer close to the umbrella and conspecifics after opening of the umbrella than control lambs (p = 0.047). An increased live weight was observed at 3 months of age for the lambs born to ewes isolated during gestation compared to control lambs and prenatally transported lambs (p < 0.050). Some gender-specific effects of prenatal stress were found: prenatally transported and isolated males entered more sections and spent more time in the object section during a novel object test than control males while no differences were observed in the females. The effects of prenatal stress on lambs born to ewes isolated during pregnancy were similar to those observed for lambs born to transported ewes but were however more rarely significantly different from controls. These results were found consistently at 1 and 3 months of age. Differences in maternal glucocorticoids as well as the modification of maternal behaviour and emotional reactivity of the ewes in the presence of a human due to repeated stress during pregnancy might be partly responsible for the modification of the reactivity of the offspring.