Individual differences in testosterone and corticosterone levels in relation to early postnatal development in the...

Many aspects of an animal's early development contribute to the emergence of individual differences in physiology. Here we asked whether litter size, birth mass, suckling success and postnatal growth were predictors of individual differences in testosterone (T) and corticosterone (CORT) levels in neonatal domestic rabbits. Serum concentrations of both hormones, which we measured on postnatal day 8, were significantly and positively correlated with pup growth and milk intake. Litter size and birth mass were not significantly correlated with levels of T and CORT, although both parameters were indirectly associated with the levels of these hormones via their effects on milk intake and pup growth. Our results highlight the importance of naturally occurring features of the postnatal environment in shaping individual differences in T and CORT levels during early life.