Implications of commercial cross-fostering in large litters when low body weight of piglets is the main criterion

Litter management aimed at reducing losses is crucial in intensive pig production, with cross-fostering (CF) being a commonly used approach. CF is a major challenge, especially in the breeding of highly prolific sows. We therefore investigated the efficiency of non-experimental CF under farm conditions. A total of 360 piglets (Choice Genetics − Naima sows × P76 boars) from 25 sequential litters were included in the observational study. Four litters with 48 piglets represented the control group and in the remaining 21 litters, 51 piglets (CF piglets) were cross-fostered according to the farm's standard procedure of mixing litters by body weight. The piglets were transferred to a specific foster sow in a way that piglets from 2 to 10 different litters were mixed. The CF piglets were lighter than the residents and the control piglets. The piglets that died had lower body weight than the survivors, especially in the CF group (≈35 %). Half of the CF piglets died a few days after birth, while mortality was 13 % in the residents and 8 % in the control group, resulting in a tendency of higher mortality in CF litters (19 %) compared to the control group. The unusually high mortality was mainly related to CF litters with more than two litters combined. Therefore, combining multiple litters and the use of low piglet birth weight as the main CF criterion does not seem to be justified from both a production and welfare point of view and could even have the opposite effect and increase mortality. To reduce mortality, other strategies could be tested (e.g. moving heavy piglets) and/or other CF criteria considered (e.g. teat order, litter size, parity).