Effects of repeated cross-fosterings on preweaning behavior and growth performance of piglets and on maternal behavior of sows

Extensive cross-fostering is widely used in early-weaning units in order to standardize and improve body weight at weaning. However, young suckling pi glets develop teat fidelity and repeated cross-fosterings could go against this behavior. This experiment was therefore conducted to compare the behav ior and growth of 13 control and 14 fostered litters. Once every 3 d (from d 1 to 16 of lactation), all piglets were weighed and three piglets were sw itched between two fostered litters. Their unfestered littermates were call ed residents. Behavior was recorded for 2 h after weighing and(or) adoption and during one nursing period 24 h later. Fights were more frequent (P < 0 .05) in treated than in control litters during and between nursings at all ages of adoption except d 1. Most fights occurred between resident and fost ered piglets (P < 0.001), except at d 1. Fights during nursing were still m ore frequent in treated than in control litters 24 h after adoption (P < 0. 02), except at d 1 and 16. More piglets had skin lacerations in treated tha n in control litters except at d 1 (P < 0.05), and scratches were more freq uent in fostered than in resident piglets at d 1 (P = 0.07), 7, 13, and 16 (P < 0.01). At all ages except d 1, failed nursings and snaps at piglets we re more frequent in fostered than in control litters (P < 0.05), most snaps being directed at adopted piglets (P < 0.001). In fostered litters, sows s pent 15 to 30% less time lying on their sides at d 4, 7, 13, and 16 (P < 0. 05). Finally, adopted piglets were 13% lighter than controls at weaning (P < 0.001), whereas residents were heavier than adopted piglets (P < 0.05) bu t lighter than controls (P = 0.1). These data demonstrate that cross-foster ing done repeatedly during lactation is stressful for piglets and sows and does not improve body weight at weaning.