Behavioral and physiological responses to early weaning in ewes and their single or twin lambs.

As during the early postpartum, ewes and their twin lambs have a weaker bond than ewes that rear single lambs; it might be expected that early artificial weaning would trigger less intense behavioral and physiological responses in mothers and their twin lambs than in mothers and their single lambs. The aim of this study was to compare the behavioral and physiological responses of ewes and their twin or single lambs to early weaning. The study was performed with 19 Saint Croix ewes: 10 bearing single lambs and nine bearing twins (data from only one sibling from each pair of twins was collected). Lambs were weaned at 43 days old. Body weight, stress-related behaviors, and blood protein concentrations were recorded in ewes and lambs before and after weaning. Single lambs were heavier and paced more frequently during the day of weaning than twin lambs (10.6 ± 0.4 vs 8.9 ± 0.4 kg; P = 0.007 and 4.1 ± 0.4 vs 1.5 ± 0.4%; P = 0.0003, respectively). In addition, ewes rearing single lambs paced and vocalized more than twin lambs' mothers the day of weaning (pacing, 42.4 ± 1.1 vs 20.0 ± 1.2%; P < 0.0001; vocalizations, 43.1 ± 2.6 vs 21.3 ± 2.7%; P < 0.0001). Litter size affected only ewes' albumin concentration, without other effects in protein concentrations in ewes or lambs. In conclusion, early weaning triggered stronger behavioral responses in mothers and their single lamb than in mothers and their twin lambs.