**Background:** In commercial pork production, piglets are weaned abruptly between 2.5 and 5 weeks of age, which induces significant physiological and psychological stress. This contrasts with natural conditions where weaning occurs gradually between 14 and 18 weeks of age. The sudden change in diet, environment, and social grouping causes upregulation of the HPA axis, increased cortisol levels, reduced feed intake, gastrointestinal dysfunction, and behavioral disorders. Historically, interventions focused on nutritional strategies and post-weaning housing, but recent attention has turned to pre-weaning management systems that promote natural social behaviors. This review summarizes the literature on two such strategies: co-mingling of non-littermates before weaning and intermittent suckling (IS), a form of gradual separation from the sow.
**Methods:** The authors conducted a narrative review of the literature related to co-mingling and IS, examining their effects on weaning-associated stress, behavior, performance, mortality, gastrointestinal function, and immunocompetence. The review first describes the development of social and eating behaviors of pigs in semi-natural conditions, then summarizes the effects of commercial weaning practices, and finally synthesizes findings from studies on co-mingling and IS across various housing systems, group sizes, and timing protocols. A comprehensive table (Table 2) catalogs 60+ studies on co-mingling variants, and Table 3 summarizes 20+ studies on IS regimens dating back to 1961.
**Key Results:** For co-mingling, numerous studies demonstrated reduced aggression among socialized piglets immediately after weaning, independent of housing system, group size, and age at start of co-mingling. For example, Van Kerschaver et al. (2021) showed co-mingled piglets had fewer skin lesions at shoulders and flanks post-weaning. Post-weaning performance benefits were observed in several studies: Hessel et al. (2006) found co-mingled piglets gained 290 g more in the first week after weaning and 1.09 kg more over 9 weeks. Van Nieuwamerongen et al. (2015) reported 69% greater weight gain between day 1 before and day 2 after weaning, and 81% more feed intake. However, some studies found no effect on post-weaning performance. Pre-weaning mortality was typically higher in multi-litter systems (14–17% vs. 8% in conventional systems, Marchant et al., 2000), primarily due to crushing. For IS, separation times of 12 h per day consistently increased creep feed intake. Berkeveld et al. (2009) found that one week of IS (10 h separation/day) before weaning at day 26 prevented post-weaning villus atrophy even without improved feed intake. IS pigs showed lower manipulative behavior and higher relaxed behavior post-weaning, supported by reduced cortisol levels. When IS was combined with extended lactation (33 days), it prevented villus atrophy compared with conventional weaning (Nabuurs et al., 1996). A study combining multi-suckling, IS, sow-controlled housing, and extended lactation (van Nieuwamerongen et al., 2017) prevented the growth check at start of IS and at weaning, with 83% of sows showing estrus in lactation and 95% pregnancy rate.
**Clinical Implications:** Pre-weaning socialization and gradual separation from the sow are potentially adaptable to commercial settings and may reduce post-weaning stress, improve welfare, and enhance performance and gastrointestinal function. Co-mingling between 7 and 14 days of age aligns with natural social development. For IS, separation times of 12 h or more per day are more likely to stimulate creep feed intake, but even shorter separations may confer benefits through non-nutritional mechanisms. The combination of both techniques may produce additive benefits. Economic viability will depend on the level of performance and welfare improvements achieved and potential reductions in post-weaning medication use. Key factors influencing success include timing of co-mingling, group size, housing system, separation duration, and age at IS initiation.