Growing up side by side: Social attachment between twin lambs and the role of the mother's presence

Abstract

Twin lambs establish a social attachment soon after birth, which implies that they prefer to interact with each other during the suckling period. However, the role of the mother's presence in maintaining the social attachment between twins has been scarcely studied. The aims of this study were to characterize the dynamics of the distance between twin lambs during lactation until three months after weaning, and to determine the impact of the mother in this regard. The study was performed with 11 East Friesian multiparous ewes, nine Finnish Landrace multiparous ewes, and their twin lambs under grazing conditions. The distances among all lambs of the flock were measured from aerial pictures taken with a drone in three periods: before weaning (on 33, 49, 62 and 78 days of age); before and after a temporary maternal separation (on 79, 81, 82 and 83 days of age) and immediately before and after weaning [ 94, 95, 96, 98 (weaning day), 99, 110, 124, 145 and 186 days of age]. The mothers and their lambs were temporarily separated at 81, 82, and 83 days of age to determine if the distance between siblings differed when the mother was absent. Distances between siblings vs the mean distance from each twin to the other lambs of the flock, and the distance between siblings vs the distance from each twin lamb to its' mother, were compared separately during the aforementioned periods. The sibling lambs were closer to each other than the other lambs of the flock before and after weaning (P < 0.0001, for both). While the distance between siblings increased from 49 to 78 days of age (P = 0.01), the distance from each twin lamb to its' mother did not change. After the temporary maternal separation, the distance between siblings was shorter than the mean distance from each twin to the other lambs of the flock (P < 0.0001). The distance between siblings increased from 33 to 78 days of age (P ≤ 0.03), while the mean distance from each twin to the other lambs of the flock did not change. The distance between siblings and the mean distance from each twin to the other lambs of the flock decreased from 94 to 96–98 days of age (P < 0.0001). From 98–110 days of age, the distance between siblings and the mean distance from each twin to the other lambs of the flock increased (P < 0.0001). In conclusion, twins had a preferential social attachment to each other, that was gradually weakened during their development. The social attachment between siblings was likely because of their mother’s presence, as it gradually disappeared after abrupt weaning.