Effects of the proportion of the litter cross-fostered and number of source litters used to create a cross-fostered litter on piglet pre-weaning performance.

The objective of this study was to determine the effects of the proportion of a litter that was cross-fostered and the number of source litters used to form a cross-fostered litter on piglet pre-weaning performance. The study was carried out at 2 commercial farrowing facilities using a RCBD with 53 blocks (265 litters, 3675 piglets). Sows within a block were of similar parity, body condition score, and functional teat number that farrowed at the same facility on the same day. Litters within a block were the same size after cross-fostering (13 or 14 piglets), with similar average and CV of piglet birth weight. Treatments involved the percentage of piglets in the litter that were cross-fostered (0% = none; 50% = half from birth sow, half from other litters; 100% = all from other litters) and number of source litters (sows to which piglets were born) contributing piglets to the cross-fostered litter. The 5 cross-fostering treatments (% of litter cross-fostered/number of source litters) were: 1) 0%/1 (all piglets from birth sow); 2) 100%/1 (all piglets from one other sow); 3) 100%/multiple (all piglets from 6 to 11 other sows; mean 6.8); 4) 50%/multiple (half piglets from birth sow; half piglets from 4 to 8 other sows; mean 5.5); 5) 50%/2 (half piglets from birth sow; half piglets from one other sow). Piglets were weighed and allotted to treatment 24 hour after birth and weighed at weaning (WW; 19.2 ± 0.97 d); pre-weaning mortality (PWM) was recorded. Data were analyzed using SAS; models accounted for the fixed effect of cross-fostering treatment and random effects of farrowing facility and block within farrowing facility. There were no interactions ( > 0.05) between farrowing facility and cross-fostering treatment. There were no differences ( > 0.05) between 0%/1 and 100%/1 treatments for PWM or WW, indicating no effect of cross-fostering per se. There were no differences ( > 0.05) between 100%/multiple and 50%/multiple treatments for PWM or WW, indicating no effect of proportion of the litter cross-fostered. Pre-weaning mortality for the 0%/1 and 100%/1 treatments was greater (3.2 to 5.7 percentage units;  ≤ 0.05) compared to the other 3 treatments, which were similar ( > 0.05). Neither cross-fostering per se nor the proportion of the litter cross-fostered affected piglet performance; however, cross-fostered litters created with piglets from multiple sources had lower pre-weaning mortality than those created with piglets from a single litter.