Verdon et al. (2016).

Population:	Landrace x Large White, piglets, (Australia).
Sample size:	Before weaning: 72 litters (642 piglets). For group lactation pens, n = 6 sows and litters per pen. After weaning: The average group size at mixing was 35.7 piglets (range 29–40).
Intervention details:	Pre-weaning treatment groups: Initially, sows were allocated to either farrowing crate (FC, n = 36 sows) or Piglet and Sow Alternative Farrowing Environment (PigSAFE) (PS, n = 36 sows). At day 14, 12 sows in FC and 12 sows in PS were randomly selected to group lactation pens (GL-FC and GL-PS) respectively. Group 1 farrowing crate, no socialisation (FC): n = 24 litters. Housing design: In a farrowing crate with sow and littermate-only from days 0–27. Group 2 PigSAFE pen, no socialisation (PS): n = 24 sows / litters, number of piglets unknown. Housing design: In a PigSAFE pen with sow and littermate-only from days 0–27. Group 3 farrowing crate then group lactation, with socialisation (GL-FC): n = 12 litters, six sows/litters per group lactation pen. Socialisation housing design: In a farrowing crate with sow and littermates from days 0–14, then transferred to group lactation and stay until weaning days 27. Socialisation group size: six litters per pen (socialisation group size is the number of litters that interact with one another during lactation). Group 4 PigSAFE pen then group lactation, with socialisation (GL-PS): n = 12 litters, six sows / litters per group lactation pen. Socialisation housing design: In a PigSAFE pen with sow and littermates from days 0–14, then transferred to group lactation and stay until weaning day 27. Socialisation group size: six litters per pen.
Study design:	Non-randomised controlled trial.
Outcome studied:	Weaning age: average 27.3 days (range 24–30). Socialisation length: 13 days. Regroup condition: FC = four litters, unfamiliar. PS = four litters, unfamiliar. GL = two litters from GL-FC and 2 litters from GL-PS, unfamiliar, such to maximise the number of unfamiliar group lactation litters being mixed post-weaning. Post-weaning group size: average 35.7 piglets (range 29–40).  Familiarity ratio / unfamiliar piglets percentage: GL: 50% (range 44–56%), FC: 75% (range 70–81%), PS: 75% (range 63–86%). Behavioural indicators: Behaviours: for 2 hours after regrouping: Bouts of aggression. Fights (latency to fight, fighting frequency, average fight duration and total duration fighting). Skin lesions (six piglets per litter randomly selected, n = 432 piglets): on the day before weaning (day 26), and 24 hours post-mixing (day 28). Measured total number of skin lesions on three zones (front, middle and rear).
Main Findings (relevant to PICO question)	Behavioural indicators: Behaviours: for 2 hours after regrouping. Bouts of aggression: GL < FC or PS (significant, P < 0.01). Latency to fight: no significant difference. Fighting frequency:  GL < FC or PS (significant, P < 0.01). Average fighting duration: GL < FC (significant, P = 0.04) but not PS. Total duration fighting: GL < FC (significant, P < 0.01), but not PS. Skin lesions: GL < FC or PS 24 hours post-mixing (significant, P < 0.01).
Limitations:	While GL-FC and GL-PS were randomly selected from FC and PS, the allocation method of sows / litters to PS and FC was unknown. There was a range of weaning age. GL piglets had a higher proportion of familiar piglets in the pens after regrouping. Skin lesions were assessed in randomly selected focal piglets rather than all piglets. The number of assessors for behaviours and skin lesions was not specified. Number of piglets in each pre-weaning treatment group, and total number of piglets after weaning were unknown.