Space density affects resting location and proximity of fattening pigs at night

• The proportion of rest at night did not depend on space allowance • Less space per pig increased the probability of lying on the slatted floor • Less space per pig increased the probability of lying in full contact with others • More space per pig allowed pigs to lie alone on the solid floor Night rest is an important component of animal welfare, which may be compromised by high stocking density in fattening pigs. This study investigated how varying space density, achieved by reducing the number of pigs per pen, affect resting location and proximity to other pigs at night throughout the fattening period. A total of 197 pigs across 18 pens were assigned to one of three treatments: 0.7 m²/pig (0.7M, 18 pigs per pen), 1.4 m²/pig (1.4M, 9 pigs per pen), or 2.1 m²/pig (2.1M, 6 pigs per pen), from 30 kg to ∼110 kg (11 weeks). On weeks 2, 5, and 10, night video recordings (22:00–07:00) were scanned every 10 min to assess the proportion of pigs resting on different floor types (solid, drained, slatted), and proximity to others (alone, close contact, full contact). All treatments showed a similar overall proportion of pigs lying during the night hours of 95 %. However, 0.7M pigs had a higher probability of resting on the slatted floor (P < 0.01), while 1.4M and 2.1M pigs had a higher probability of resting on the solid floor (P < 0.01). 0.7M pigs also showed more full-contact resting compared to 2.1M (P < 0.01), while 1.4M and 2.1M pigs rested more often without contact by week 10 (P < 0.01). In week 10, 1.4M pigs rested more on the drained floor and showed more full-contact resting than 2.1M (P < 0.01). These findings suggest that high stocking densities may hinder pigs’ possibility to rest on the solid floor and limit their capacity to rest alone, potentially compromising welfare.