Psychosocial maternal stress during pregnancy: effects on reproduction for F0 and F1 generation laboratory rats.

The impact of daily social maternal stress on reproduction parameters was studied in F0 and F1 generation female Long-Evans rats. Chronic maternal stress was induced in pregnant females (F0 females) by 2 h social confrontation with a dominant female throughout pregnancy. Social stress of F0 females was associated with lower maternal body mass investment in litters. While maternal stress did not cause a decline in the F0 female mass, it resulted in reduced litter sizes and lower litter masses. The individual body mass of offspring from stressed (= prenatally stressed offspring, PS) and control F0 generation mothers (= prenatal control offspring, PC) did not differ at birth. However, PS offspring grew faster during lactation and were therefore heavier than PC offspring at weaning. Reproduction parameters of F1 generation females were determined until an age of 180 days. Investigation revealed that PS females did not differ from PC females in any reproduction parameter assessed, except for higher PS offspring body mass at birth. It was also observed that a higher percentage of PS females gave birth outside the core breeding period during the light (= inactive) period. This study shows that exposure to a relatively mild social stressor during pregnancy alters female reproduction in rats. However, there was no indication of higher infant mortality which is often associated with severe laboratory stress. We argue that the reduced litter sizes in stressed F0 mothers represent an adaptive strategy from an evolutionary point of view.