Canadian researchers have found that crossfostering of piglets after day 1 of age disrupts suckling patterns and impairs sow and piglet welfare.

Researchers found increased fighting, ambulation, vocalizations and skin lesions were more likely for fostered pigs. Sows receiving the fostered pigs were more aggressive toward the alien piglets. In addition, pigs that were fostered were lighter at weaning than pigs in their original litter.

To start the experiment, researchers at the Lennoxville Research Centre and College of Veterinary Medicine of St. Hyacinthe, Quebec, induced farrowing of 27 sows. Thirteen litters were used as controls and 14 litters as fostered litters. All litters were standardized to 11 pigs (plus or minus one pig) within 26 hours of birth.

Every three days, researchers weighed all pigs and switched three pigs between a pair of litters. Fostered litters were paired according to their time of birth (within 12 hours). The protocol was to take the three heaviest pigs from the lighter litter and switch them with the three lightest pigs from the heavier litter.

A piglet could be fostered from zero to five times between birth and weaning, on days 1,4,7,10,13 and 16. Weaning was at 18 days of age.

The behavior of sows and piglets was recorded during the first two hours after weighing or fostering. Researchers counted the number of fights between pigs at the udder or elsewhere in the crate and the number of successful and unsuccessful nursings. They also recorded the number of aggressive events (sows snapping at pigs). The identity of the pigs (control, resident and foster) also was recorded.

Fights between pigs were more frequent in fostered litters. Most fights were at the udder, with piglets fighting to gain access to a specific teat. Fights between resident pigs (those that remained in their original litter but had fostered littermates) and fostered pigs were more likely. Fostered pigs were more likely to have lacerations on their face and body.

Sows with fostered pigs in their litter were less likely to let down milk and more likely to snap at fostered pigs.

While not statistically significant, researchers found that control pigs were heavier at weaning than resident pigs. Fostered pigs were lighter than either the control or resident pigs.

Researchers: Suzanne Robert, Dairy and Swine Research and Development Centre; and G.P. Martineau, Ecole Nationale Veterinaire de Toulouse. Phone Robert at (819) 565-9174 ext. 219 or e-mail