D’Eath (2005).

Population:	[Sow: Large White X Landrace] x [Boar: Large White], Piglets, (UK).
Sample size:	Before weaning: 16 litters (198 piglets). Selected based on: close parturition time, with at least nine piglets (preferred).After weaning: 128 piglets. Selected eight healthy focal piglets (at least 6 kg) randomly from each litter, housed in one pen until regrouping.
Intervention details:	Pre-weaning treatment groups: Group 1 (control): no socialisation, n = 8 litters. Housing design: littermate-only with sow in a farrowing crate until weaning day 30. Group 2 (socialised): n = 8 litters. Socialisation housing design: littermate-only with sow in a farrowing crate until day 10, then socialise days 10–30 by removing a barrier between two adjacent pens. Socialisation group size: two litters per pen.
Study design:	Non-randomised controlled trial.
Outcome studied:	Weaning age: day 30. Socialisation length: 20 days. Regroup condition: Regrouped at day 50. Four piglets were selected at random from two unfamiliar litters. Post-weaning group size: eight piglets. Familiarity ratio: 1:1. Growth performance: Mean weight gain/Average daily weight gain (ADWG): days 0 (at birth), 9, 15, 21, 30, 45, 50, 55 and 60 of age. (Entire experiment and after regrouping). Behavioural indicators: Behavioural record. Fight (reciprocal). Bullying (one-sided). Skin lesions: days 51, 52 and 60. Food competition tests: days 37, 43 (pre-regrouping) and 57 (after regrouping).
Main Findings (relevant to PICO question)	Growth performance: Mean weight gain / Average daily weight gain (ADWG): no significant difference between treatment groups for the entire experiment or after regrouping. Behavioural indicators: Behavioural record. Day 50, latency to the first fight: socialised group < control group (significant, P = 0.034). Day 50, mean duration of fights: control group > socialised group (significant, P = 0.046). Day 51, frequency of bullying: control group > socialised group (significant, P = 0.039). Day 51, for fights with clear winner, the proportion of fights initiated by the eventual winner: socialised group > control group (significant, P = 0.048). Skin lesions:  By day 61: socialised group < control group (significant, P = 0.008). Food-competition tests:  result was not reported in D’Eath (2005) paper.
Limitations:	Treatment group allocation method was not stated. Number of piglets in each pre-weaning treatment group was not specified. Number of post-weaning groups from each pre-weaning treatment group was not specified.  Total number of piglets was unknown after regrouping at day 50. The regrouping was not stated to be within the pre-weaning treatment group. While two assessors were used for skin lesions, due to significant systematic difference, the second person’s data was discarded, resulting in insufficient data at day 51 and reduced sample size at day 52, n = 96; day 60, n = 80. Regrouping did not immediately happen at weaning. Sampling frequency in a day or length of recording for aggressive behaviours were not specified. Food competition test result was not reported in D’Eath (2005) paper.