EFFECTS OF LITTER SIZE ON THE VOCAL BEHAVIOR OF EWES

Three experiments were carried out to compare the vocal behaviour of ewes rearing single, twin and triplet litters, and to investigate the importance of ewe bleats in eliciting the approach of a neonatal lamb separated from its dam. In Experiment 1, bleating behaviour of ewes was measured when their litters were aged between 6 and 12 h. Compared with ewes rearing single lambs, ewes rearing triplets bleated more when their litters were intact, but less when one of their lambs was removed (P < 0.01). When the removed lamb was replaced 10 m from the ewe, bleating increased but the more lambs a ewe was rearing, the less likely she was to approach the separated lamb, and only 70% of triplet litters. compared with 91% of twin litters and 100% of single litters, were reunited within 5 min. In Experiment 2, bleating behaviour was measured when litters were 2 and 5 weeks old. Ewes rearing single and twin lambs bleated more than ewes rearing triplet lambs (P < 0.01), but the bleating response to removal of a lamb was uniform across all litter sizes. A third experiment demonstrated that a 6-12 h old lamb which was separated from its dam was more likely to approach a ewe that was bleating than a silent ewe (P < 0.01), thus ewe bleats probably aid long-distance recognition of the dam. The results from the three experiments were consistent with previous observations that lambs from multiple litters were often separated from their dams.