Colostrum mediates the development of mother preference by newborn lambs

The first sucking bouts have strong rewarding properties in the establishment of a preference for the mother by newborn lambs. In this study we designed an artificial teat (Experiment 1) and a method of tube feeding (Experiment 2) to investigate the role of nonnutritive sucking and colostrum intake as reinforcers in the development of this relationship (Experiment 3). In this third experiment, lambs of the control group (n=10) had free access to the udder. In the other groups they were prevented from sucking between birth and 6 h by covering the ewe's udder while lambs received one of the following treatments: access to nonnutritive teats fitted onto the mother's udder (n=12), tube fed with colostrum (n=11), or fully deprived (n=10). When tested in a two-choice test at 24 h of age, controls and lambs receiving colostrum spent significantly more time near their mother than near the alien ewe. By contrast, deprived lambs did not. Half of the lambs having access to nonnutritive teats displayed a preference for their mother; the other half chose the alien ewe. However, most lambs that were affected by the treatments displayed a preference for their mother when a second test was performed at 48 h. In conclusion, these results demonstrate that a neonatal nasogastric infusion of colostrum has the same rewarding properties as a complete sucking bout. They also provide evidence for the first time that a relationship with the dam can be established via a nutritional signal originating from the gastrointestinal sphere.