Effects of cross-fostering within 24Â h after birth on pre-weaning behaviour, growth performance and survival rate of biological and adopted piglets

Cross-fostering is the transference of piglets to equalise litter size according to the birth weight. In many commercial farms piglets are usually grouped in litters with 100% adopted piglets. The aim of the experiment was to assess the behaviour of piglets during the suckling period as well as to assess their performance and mortality rate up to weaning in litters with different composition in terms of adopted and biological piglets. Three treatments were studied: 100B (100% biological piglets, n=13), 50B50A (50% biological piglets and 50% adopted piglets, n=13) and 100A (100% adopted piglets, n=13). All litters were standardised to eleven piglets on average within 20.1±0.4 h (14.3-24.7 h) of birth. The behaviour of piglets was recorded during four consecutive sucklings for four days (days 1, 2, 4 and 6 after farrowing, considering day 1 as the cross-fostering day). The observations were performed at two time periods: TP1 (from release of piglets out of creep box until milk letdown) and TP2 (from the end of milk letdown up to 15 min later). Piglets were weighed at days 1, 4, 7, 10, 13 and 16. There were no differences (P>0.05) among the treatments in the following behavioural variables: percentage of missed nursing episodes; number of fights for teats and percentage of piglets involved in fights at TP1; percentage of piglets vocalising at TP1 and at TP2; number of fights per piglet elsewhere in the cage and percentage of piglets involved in these fights; number of instances of playful behaviour per piglet and percentage of piglets involved in it. At TP2 of day 1, 100B piglets displayed a lower number (P<0.05) of fights for teat (0.9 vs. 1.6 vs. 1.4 for 100B, 100A and 50B50A, respectively) and tended to have a lower percentage (P<0.07) of piglets involved in these fights than 100A (49.6%, 67.2% and 64.9% for 100B, 100A and 50B50A, respectively). Nutritive nursing episodes (overall medians of 4.0, 3.0, 4.0 and 4.0 for days 1, 2, 4 and 6, respectively), survival rate (overall 97.2%) and average weight of piglets (1983 g, 2650 g, 3411 g, 4207 g and 5047 g for days 4, 7, 10, 13 and 16, respectively) were similar (P>0.05) among treatments. Cross-fostering performed on average at 20 h after birth has no adverse effects on survival and growth performance of adopted piglets.