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 whether neonatal sucking was a potent reinforcer in the establishment of this preference by temporarily covering the udders of ewes after parturition. Lambs were assigned to one of three treatments: they had free access to the udder (group 1) or were prevented from sucking either between birth and 6 h afterward (group 2) or between 12 and 18 h after birth (group 3). Measurements of cholecystokinin plasma levels at birth and at 6 and 18 h showed that all lambs ingested some colostrum when the udder was made accessible. When tested in a two-choice test situation at 24 h of age, lambs from group 1 spent significantly more time near their mothers than near the alien ewes, those from group 2 did not show any discrimination, and lambs from group 3 clearly preferred the alien 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 displayed no preference. In a second experiment, we attempted to determine whether 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 dams when tested at 24 h of age, unlike those of groups 1 and 3. When a second test was performed at 4 days of age, all the lambs showed a strong preference for their dams. We concluded that sucking has strong rewarding properties in the establishment of a preferential relationship with the mother by the lamb. On the other hand, the maintenance of this preference does not rely on sucking as strongly.
Nowak
R
R
Laboratoire de Comportement Animal, Station de Physiologie de la Reproduction des Mammifères Domestiques, INRA, Nouzilly, France.
Murphy
T M
TM
Lindsay
D R
DR
Alster
P
P
Andersson
R
R
Uvnäs-Moberg
K
K
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002766:Cholecystokinin / Q000097:blood; D005260:Female; D008297:Male; D009035:Mothers; D012756:Sheep; D013391:Sucking Behavior / Q000502:physiology*
D002766:Cholecystokinin