Cross-suckling and nursing synchronisation in group housed lactating sows

Group housing systems for lactating sows with piglets enable the animals to behave more naturally than traditional restrictive systems. However, pigle ts may occasionally suckle from other sows than their mother. The influence of litter size, age of the litter, mother parity, piglet gender and, in pa rticular, nursing synchronisation, on the following: the occurrence of cros s-suckling (presence of alien piglets at the udder during milk ejection); c ross-suckling strategies; and piglets' success at achieving nursings, was i nvestigated. The observations were carried out on six stable groups of thre e or four unrelated sows with their piglets between 19 and 32 days postpart um. Cross-suckling was frequent (occurred in 29% of all suckling events). T he 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 suckli ng only alien sows, belonged to larger litters than piglets suckling only t heir own mother (Wilcoxon signed rank T-test; n = 6; P < 0.05). Sows with l arger litters were preferred targets for cross-suckling (Wilcoxon signed ra nk T-test; n = 78; P < 0.001). Piglets from older litters cross-suckled mor e 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 cros s-suckling. The higher the number of sows which had nursed just before a fo cal 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 b elonging 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 <less than> 0.01). Permanently cross-suckli ng, occasionally cross-suckling and faithful piglets achieved a similar num ber of suckling events indicating that these strategies may be equally succ essful in a stabilised multi-suckling situation. Mother parity and piglets' gender had no effect on cross-suckling. (C) 2001 Elsevier Science B.V. All rights reserved.