Creep heating in outdoor farrowing huts may increase piglet welfare without impacting survival and growth

Newborn piglets are prone to hypothermia, and higher mortalities are suggested in outdoor farrowing huts. Therefore, we investigated whether creep heating during the first 7 days after parturition improves piglet survival and welfare. Data (location, behaviour, weight, mortality) were collected from birth to weaning at 7 weeks from 88 litters across seasons. Each hut contained four pens, half with a heated (HEAT) piglet creep area and half of these had a metal bar (‘pendulum’) to support the sow's lying-down movement. The position of the sow at birth influenced the first piglet entry to the creep (rump facing creep: median 87 min vs snout facing creep: 191 min after the birth of the first piglet; P = 0.037). During the first day of life (D0), creep usage was low (2.6 ± 0.65 % of observations) regardless of heating (P = 0.20) and season (P = 0.38; spring: 1.5 %, summer: 2.7 %, autumn: 1.8 %, winter: 3.1 %). Most piglets on D0 were at the udder (71.5 ± 1.83 %) or in the pen, away from the sow (25.9 ± 1.87 %). Creep usage increased after D0, with more piglets inside if heated (D2, HEAT: 28.0 ± 3.16 % vs not: 6.8 ± 1.85 %; P < 0.001), at the expense of being in the pen without sow contact (HEAT: 16.6 ± 2.76 % vs unheated: 32.5 ± 3.06 %; P < 0.001). HEAT did not influence piglets in udder contact (e.g. on D2, P = 0.21). We found no effect of HEAT on piglet survival (P = 0.54) and growth (P = 0.35) based on weighing individuals D1, D21, and D49. From D1 to weaning, 16.2 % of liveborn piglets died. The risk of piglet dying tended to higher in piglets being fostered by another sow (in contrast to their biological mother; P = 0.085) and higher for males (Hazard ratio vs females: 1.4; P = 0.004). Piglet Average Daily Gain (ADG) decreased with increasing litter size at weaning (P < 0.001) and was positively associated with the parity of the sow (P = 0.042). Season influenced the piglet ADG (P < 0.001), being higher during spring (g/day: 321 ± 12^a) and autumn (338 ± 12 ^a) than summer (272 ± 11^b; winter: 297 ± 14^ab). Piglets fostered by another sow had lower ADG (283 ± 13 vs native piglets of the litter: 331 ± 5 g/day; P < 0.001). In conclusion, heating resulted in more piglets using of the creep early in life on postnatal day 2, especially in cold weather (mean outdoor temperature effect; P = 0.030), indicating a need for more thermal zones inside the hut. These results suggest that additional hut features like heating may increase piglet welfare.