Development of mother discrimination by single and multiple newborn lambs.

Most research on recognition of the ewe by her lamb has focused on lambs several days or even several weeks old, whereas newly born lambs have received little attention. The aim of this work was therefore to study the attraction of Merino lambs to postparturient ewes and their ability to discriminate between their own and alien mothers in a two-choice situation 12, 18, 24, 48, and 72 hr after birth. A comparison between singles and multiples was also made in 18 and 24-hr-old lambs. When released in the testing pen, approximately 90% of the lambs in each group (older than 12 hr) spent more than 3 min with the two ewes during the 5-min test. It was only from 24 hr old, however, that a high proportion of lambs spent at least two-thirds of this time close to their own mothers (correct choice). The proportion of singles spending more than 3 min with the ewes or making a correct choice was higher than that of multiples. This effect was related to litter size but not to birth weight. It is concluded that a majority of Merino lambs are clearly attracted to ewes by the time they are 18 hr old and can discriminate their own dams from alien mothers at about 24 hr of age. At this stage singles perform better than multiples.