Cross-suckling and associated behaviour in piglets and sows

In order to reveal factors that cause piglets to become cross-sucklers and to study the behaviour associated with cross-suckling, the nursing and suckling behaviour of sows and piglets was first observed in a farrowing pen 4 to 7 days after farrowing and later in pens for group housed lactating sows (i.e., from day 5 to 14 after moving to the multi-suckling pen which occurred on day 11 after birth). Three groups of six sows and their litters (189 piglets in total) were studied. About 34% of all piglets were seen cross-suckling at least once. However, it appear that in the multi-suckling system there were at least two groups of individuals present; those that suckled alien sows habitually (16% of the piglets cross-suckled more than five times) and those that cross-suckle only occasionally (84% of the piglets cross-suckled between 0 and 4× including). Cross-suckling was found to be associated with low milk yield of the mother in the farrowing pen. The cross-suckling piglets compensated for the low milk yield by cross-suckling a sow with a higher milk yield and by moving to a teat with a higher milk yield. Interestingly, this study showed that sows distinguished between their own and other piglets, as the sows showed more aggression towards both cross-suckling and cross-fostered piglets.