Early life socialisation in pigs: a systematic review

Background Early life socialisation, or co-mingling of piglets, has been practiced and researched since the late nineties. Although studies report benefits of this management technique to help piglets in the weaning transition and subsequent regrouping events, there are contradictory outcomes, especially on production performances. The aim of this review is to provide a comprehensive and systematic overview of the literature on early life socialisation in pigs and to outline the advantages and disadvantages. Using the PRISMA guidelines, 54 peer-reviewed articles were included. Group lactation studies were excluded to provide a more standardized comparison among the included articles. Data were collected on experimental designs and outcomes. Results The review revealed two major categories, with studies aiming: (1) to improve welfare by using socialisation to avoid regrouping at weaning, and (2) to improve pigs’ social skills by co-mingling piglets at the biologically relevant time frame in their development, regardless of later regrouping events. This distinction is not explicit in the literature but has a major impact on the experimental design and the research outcomes which need to be considered when comparing studies. Overall, early life socialisation at the biologically relevant age (10–16 days postnatally) has a long-term positive impact on pigs’ social behaviour. The impact on growth is negligible. Studies on cognition, stress and immunological parameters, and the gastrointestinal tract and microbiota did not reveal major differences between treatment groups. Sows do not suffer long-term consequences from socialisation, although monitoring of udder lesions is recommended. Remaining knowledge gaps include mostly practical aspects of applying socialisation to current farm situations, such as large litter sizes. Conclusions Based on the literature, early life socialisation around 10–16 days of life between 2 and 3 litters is expected to increase piglets’ social skills and reduce aggression up until slaughter. While positive effects on growth performance can occur, this is not a certainty. Therefore, farmers interested in applying this management strategy may do so with the goal to increase animal welfare rather than to increase production performance.