Cross-fostering into smaller or older litter makes piglets integration difficult: Suckling stability-based rationale

Abstract

Cross-fostering (C-F) is a standard procedure in the rearing of piglets which involves the relocation of piglets from biological to the foster mother/litter. Piglet’s integration into the new suckling environment is of crucial importance and depends on many factors that make C-F implementation a significant challenge for pig-breeders. Here, we experimentally cross-fostered piglets of different age and body weight between 20 litters of different sizes. The study aimed to determine the impact of age, body weight, and litter size asymmetry between C-F piglets/litters on the fostered piglets suckling activity immediately after C-F. It appeared that body weight did not have any impact on the integration of piglets into the new suckling environment. Besides, we found that piglets which were older (for 1 to 1.5 day on average) than their foster peers more likely succeed to suckled successfully in the first two post-C-F suckling events (p < 0.01), while piglets transferred into older litter (for 2 days on average) were significantly non-active in suckling. Furthermore, and contrary to our prediction, piglets transferred into the litter of the same or slightly larger size than their original litter succeed to suckled successfully in the first two post-C-F suckling events (p < 0.05), with an evident passiveness of piglets transferred into the smaller litter (with 1 piglet less on average, p < 0.05). We suggested that the level of suckling order development (suckling stability/teat fidelity) dictates piglet integration into the new suckling environment. Accordingly, we found postponed or even prevented integration when piglets were transferred into the smaller or older litter, wherein the suckling order is supposed to be more robust. It appears that some of the widely used C-F methodologies (e.g., litter equalization) might compromise piglets’ welfare. We, therefore, suggest reconsidering the use of existing C-F methods.