Acute hunger of rat pups elicits increased kyphotic nursing and shorter intervals between nursing bouts: implications for changes in nursing with time postpartum.

Earlier findings, based on limited behavioral observations, indicate that nursing behavior in rats declines dramatically in duration over time postpartum-despite increasing ingestion of milk by rat pups to meet their growth and metabolic needs-although hungry pups elicit more nursing than do well-nourished pups. The authors compared the nursing pattern in detail for 6 hr on Days 7 and 14 and induced hunger in pups acutely with mammary-duct-ligated dams unable to provide milk. Compared with Day 7, on Day 14, supine nursing and the interval between nursing bouts increased, whereas hovering over pups and kyphotic nursing decreased. When pups were increasingly hungry, these age-related changes were counteracted. Thus, the ingestive motivation of pups largely regulates the nursing pattem over time.