Results of GLMM in which variation of offspring body mass at birth in subsequent litters was analysed in relation to manipulated sex and size of mothers' suckling litters, neonate's sex and maternal effort estimated as (a) daily energy expenditure (DEE) and (b) mean mass of pups from the manipulated litters at weaning. (Maternal identity was included as a random factor (with the estimates of 0.028 and 0.026, respectively). The analyses performed without the non-significant effects of litter sex manipulation and litter size revealed the same interactions of neonate sex and maternal effort.)