The nurturing ability of PVG-RT7b rats is strongly affected by the fetal environment

Our strain of inbred PVG-RT7b (PVG.7b) rats was at risk of failing to be maintained owing to frequent neonatal death. Only 23.5% of mothers succeeded in nurturing their offspring at the first parturition. Furthermore, mothers failing to nurture their offspring at first parturition also failed in the second one. Here, we investigated the cause of frequent neonatal deaths in PVG.7b rats. Exchanging newborn offspring between PVG.7b and Wistar-Imamichi (WI) rats. resulted in 80.0% of WI mothers succeeding in nurturing PVG.7b offspring, whereas only 18.2% of PVG.7b mothers succeeded in nurturing WI offspring. These findings indicate that the neonatal mortality of PVG.7b is due to maternal factors rather than inherent offspring issues. Additionally, we examined the mammary glands of PVG.7b immediately after the second parturition. PVG.7b rats, which initially failed to nurture, exhibited normal mammary gland development and milk production after the second birth. These results suggested that neonatal death is due to maternal behavior. Moreover, we investigated the nurturing ability of PVG.7b rats nurtured by WI foster mothers (PVG.7b ^Infant/WI) or born and nurtured from WI recipients after embryo transfer (PVG.7b ^ET/WI). Only 26.1% of PVG.7b ^Infant/WI mothers succeeded in nurturing their offspring, compared to 63.6% of PVG.7b ^ET/WI mothers. However, only 20.0% of PVG.7b mothers born and nursed by PVG.7b ^ET/WI succeeded in nurturing their offspring. These results suggest that the fetal environment influences the nurturing ability of PVG.7b rats.