Cross-suckling and nursing synchronisation in group housed lactating sows

Abstract

Group housing systems for lactating sows with piglets enable the animals to behave more naturally than traditional restrictive systems. However, piglets may occasionally suckle from other sows than their mother. The influence of litter size, age of the litter, mother parity, piglet gender and, in particular, nursing synchronisation, on the following: the occurrence of cross-suckling (presence of alien piglets at the udder during milk ejection); cross-suckling strategies; and piglets’ success at achieving nursings, was investigated. The observations were carried out on six stable groups of three or four unrelated sows with their piglets between 19 and 32 days postpartum. Cross-suckling was frequent (occurred in 29% of all suckling events). The main determinant of cross-suckling was litter size. Piglets from larger litters missed nursings of their mothers more often ( r s=0.72; n=22; P<0.001) and performed cross-suckling more often than piglets from smaller litters ( r s=0.54; n=22; P<0.05). Piglets, who were observed suckling only alien sows, belonged to larger litters than piglets suckling only their own mother (Wilcoxon signed rank T-test; n=6; P<0.05). Sows with larger litters were preferred targets for cross-suckling (Wilcoxon signed rank T-test; n=78; P<0.001). Piglets from older litters cross-suckled more often than piglets from younger litters ( r s=0.50; n=22; P<0.05). Nursing synchronisation (sows nursing within one minute of each other) was high at 82%. Sows nursing immediately after other sows attracted less cross-suckling. The higher the number of sows which had nursed just before a focal sow, the fewer alien piglets were then present at her nursing ( r s=−0.35; n=14; Cochran–Mantel–Haenszel (CMH) statistic; P<0.05). Piglets belonging to a specific litter were less likely to cross-suckle at an alien sow if her nursing was preceded by a nursing of the mother of that litter (CMH statistic for 28 piglets; P<0.01). Permanently cross-suckling, occasionally cross-suckling and faithful piglets achieved a similar number of suckling events indicating that these strategies may be equally successful in a stabilised multi-suckling situation. Mother parity and piglets’ gender had no effect on cross-suckling.