Physiological and behavioral consequences in rats of water recycling during lactation.

Radioactive water injected into 10-day-old rats were recovered the following day from their mothers' blood. This transfer of water was nearly eliminated by ligating the injected pups' urethras, a result indicating that mother rats consume their offspring's urine. Preventing urine consumption by ligating urethras of all pups in a litter doubled the plasma volume deficit in dams produced by 24 hr of water deprivation alone and led to increased isotonic saline, but not water, intakes following after water deprivation. Mother rats' daily water intakes increased after they were deprived of pup urine, and their pup-licking behavior increased following water deprivation. These findings indicate that urine consumption by mother rats has both physiological and behavioral consequences and suggest that pup licking is, in part, an ingestive behavior.