The influence of nutrition and postpartum mating on weaning and subsequent play behaviour of hooded rats

Female hooded rats, Rattus norvegicus, that were mildly food restricted or pregnant during lactation weaned their offspring earlier than ad libitum fed control mothers. Early weaning was inferred by lower rates of milk transfer, an earlier reduction in care-giving activities and increased unwillingness to suckle pups. However, food-restricted and pregnant mothers differed in how they weaned their offspring. Most notably, pregnant dams became highly aggressive to their pups around this time. After weaning was completed, levels of play in both groups of early weaned pups were higher than those of control pups. Thus the discovery of a relationship between early weaning and increased play, previously reported in domestic cats, Felis catus, generalizes to a second altricial species. Since details of the increased play response varied between the litters of food-restricted and pregnant mothers, the former engaging in more social play and locomotor play and the latter only in more locomotor play, this difference was attributed to the nature of the weaning process that rat pups experienced earlier.