The effect of littermate weight on survival, weight gain, and suckling behavior of low-birth-weight piglets in cross-fostered litters

Objective: To determine whether low-birth-weight piglets show better survival, weight gain, and suckling behavior when grouped with other small piglets by cross-fostering. Methods: We manipulated the number and size of foster littermates for low-birthweight piglets in 31 small (eight or nine piglets) and 22 large(11 or 12 piglets) litters. Experimental litters were composed of four to six piglets of lowest birth weight and either four to six slightly heavier or four to six much heavier piglets from two combined litters. Results: Low-birth-weight piglets raised with much heavier littermates had somewhat lower survival rates, but showed no tendency towards lower weight gains or less successful suckling behavior than low-birth-weight piglets raised with slightly heavier littermates. The somewhat higher survival rate of low-birth-weight-piglets raised with slightly heavier littermates was largely offset by more deaths in the foster littermates, so there was no overall reduction in total losses. Low-birth-weight piglets fought more when raised with slightly heavier piglets than with much heavier piglets, and they missed more nursing episodes and had smaller weight gains than littermates, regardless of littermate weight. Implications: Cross-fostering low-birthweight pigs into litters with other small pigs, compared to fostering into litters with high-birth-weight pigs, slightly improved their survival, but did not affect their weight gain or ability to suckle successfully, nor overall litter survival, even in litters as large as 11 or 12 piglets. Cross-fostering low-birth-weight pigs to litters of similar birth weight increased the level of fighting.