DEVELOPMENT OF A PREFERENTIAL RELATIONSHIP WITH THE MOTHER BY THE NEWBORN LAMB - IMPORTANCE OF THE SUCKING ACTIVITY

Lambs develop a preferential relationship with their mothers within 24 h after birth. In a first experiment, we attempted to determine wheth er neonatal sucking was a potent reinforcer in the establishment of th is preference by temporarily covering the udders of ewes after parturi tion. Lambs were assigned to one of three treatments: they had free ac cess to the udder (group 1) or were prevented from sucking either betw een birth and 6 h afterward (group 2) or between 12 and Is h after bir th (group 3). Measurements of cholecystokinin plasma levels at birth a nd at 6 and 18 h showed that all lambs ingested some colostrum when th e udder was made accessible. When tested in a two-choice test situatio n at 24 h of age, lambs from group I spent significantly more time nea r their mothers than near the alien ewes, those from group 2 did not s how any discrimination, and lambs from group 3 clearly preferred the a lien ewes. At 2 days of age, lambs from groups 1 and 3 showed a strong preference for their mothers, whereas those from group 2 still displa yed no preference. In a second experiment, we attempted to determine w hether sucking also had a reinforcing value in the maintenance of this preference. Lambs were assigned to one of three treatments: they had free access to the udder (group 1) or were prevented from sucking for 6 h either at birth (group 2) or at the age of 3 days (group 3). Lambs from group 2 did not discriminate between their own and alien darns w hen tested at 24 h of age, unlike those of groups 1 and 3. When a seco nd test was performed at 4 days of age, all the lambs showed a strong preference for their dams. We concluded that sucking has strong reward ing properties in the establishment of a preferential relationship wit h the mother by the lamb. On the other hand, the maintenance of this p reference does not rely on sucking as strongly. Copyright (C) 1997 Els evier Science Inc.