Nowak R, Murphy T M, Lindsay D R, Alster P, Andersson R, Uvnäs-Moberg K
Laboratoire de Comportement Animal, Station de Physiologie de la Reproduction des Mammifères Domestiques, INRA, Nouzilly, France.
Physiol Behav. 1997 Oct;62(4):681-8. doi: 10.1016/s0031-9384(97)00079-6.
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.
羔羊在出生后24小时内就会与它们的母亲建立起一种偏好关系。在第一个实验中，我们试图通过在分娩后暂时覆盖母羊的乳房来确定新生羔羊的吸吮行为在这种偏好建立过程中是否是一种有效的强化因素。羔羊被分为三种处理方式之一：它们可以自由接触乳房（第1组），或者在出生后至6小时之间（第2组）或出生后12至18小时之间（第3组）被阻止吸吮。在出生时、6小时和18小时测量血浆胆囊收缩素水平表明，当乳房可以接触时，所有羔羊都摄入了一些初乳。在24小时龄时进行的双选测试中，第1组的羔羊在自己母亲附近花费的时间明显多于在陌生母羊附近的时间，第2组的羔羊没有表现出任何偏好，而第3组的羔羊明显更喜欢陌生母羊。在2日龄时，第1组和第3组的羔羊对自己的母亲表现出强烈的偏好，而第2组的羔羊仍然没有表现出偏好。在第二个实验中，我们试图确定吸吮行为在维持这种偏好方面是否也具有强化作用。羔羊被分为三种处理方式之一：它们可以自由接触乳房（第1组），或者在出生时（第2组）或3日龄时（第3组）被阻止吸吮6小时。与第1组和第3组的羔羊不同，第2组的羔羊在24小时龄时进行测试时，没有区分自己的母羊和陌生母羊。当在4日龄时进行第二次测试时，所有羔羊都对自己的母羊表现出强烈的偏好。我们得出结论，吸吮行为在羔羊与母亲建立偏好关系中具有很强的奖励特性。另一方面，这种偏好的维持对吸吮行为的依赖程度没有那么强。
