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Nonnutritive sucking: one of the major determinants of filial love.

Research paper by David D Val-Laillet, Raymond R Nowak, Sandra S Giraud, Céline C Tallet, Xavier X Boivin

Indexed on: 29 Mar '06Published on: 29 Mar '06Published in: Developmental Psychobiology



Abstract

The present study investigated the rewarding effects of nonnutritive sucking on the development of a filial preference. Two experiments were conducted to test whether nonnutritive visceral and oral stimuli have reinforcing properties independent from each other or act in synergy. Lambs could interact freely with their dam but were deprived of suckling by covering the udder for the first 12 hr. In Experiment 1, suckling was prevented and replaced by human giving, in the presence of the mother, either a bottle of water (B5 and B2.5: 5% or 2.5% birth weight, BW, divided into seven portions over 12 hr) or water via tube-feeding (I5 and I2.5: 5% or 2.5% BW, also divided into seven portions over 12 hr). During a two-choice test performed at 12 hr after birth, only B5 and I5 lambs preferred their mother to an alien ewe however, B5 were faster at choosing their mother at the beginning of the test. B2.5 and I2.5 lambs made a random choice. In Experiment 2, suckling was prevented and replaced by human giving, in the presence of the mother, either a bottle of water (B2.5: 2.5% BW, divided into seven portions over 12 hr) or water via tube-feeding (I10 and I2.5: 10% or 2.5% BW, also divided into seven portions over 12 hr). During a two-choice test at 12 hr, tube-fed lambs (I10 and I2.5) preferred their mother to a human. B2.5 lambs were equally attracted to both partners and spent more time near the human than lambs from the other groups. In a test of reactivity to a human performed on neonates isolated from their mother, B2.5 lambs explored the human much more than the other lambs. The presence of the human had soothing properties in B2.5 lambs and once the human left, they were the only lambs displaying enhanced vocal and locomotor activity. In these experiments, nonnutritive gastrointestinal stimuli induced a preference for the mother whereas nonnutritive sucking led to a strong positive relationship with the human. These results suggest that when lambs suckle their dam, the development of filial bonding is facilitated through the combined effects of oral and gastrointestinal stimuli.