Strain-dependent differences in maternal care and early developmental trajectories in laboratory rats

Understanding how maternal behavior varies among laboratory rat strains is essential for improving the translational relevance of preclinical models of early neurodevelopment. In this study, we compared maternal caregiving patterns and early offspring development in three commonly used rat strains: Wistar, Sprague-Dawley (SD), and Spontaneously Hypertensive Heart Failure (SHHF), under standardized experimental conditions. Maternal behaviors were recorded from postpartum day (PPD) 1-5 during light and dark phases and analyzed using conventional frequency-based measures and behavioral transition network analysis. Offspring development was assessed from postnatal day (PND) 6-22, including somatic growth, eye opening, reflex maturation, and ultrasonic vocalizations (USVs). Strain-dependent differences were observed in both frequency and organization of maternal behavior. SD dams exhibited lower frequencies of active nursing behaviors and reduced behavioral transitions, while SHHF dams showed reduced transitions and increased off-nest events, particularly during the dark phase. Network analysis revealed a distinct pattern of behavioral organization across strains, capturing dynamic features of caregiving. Developmental outcomes also varied across strains, with SHFF pups showing delayed eye opening, reduced body weight gain, and slower reflex maturation relative to Wistar and SD pups. Analysis of isolation-induced USV revealed that both SD and SHHF pups emitted fewer and shorter calls, particularly in the low frequency range, and that no consistent maternal potentiation effect emerged at any postnatal age in any strain. These findings highlight the role of strain background in early maternal care and development, with SHHF emerging as a relevant model of early-life vulnerability with translational relevance.