Minimal floor space allowance for gestating sows kept in pens with electronic sow feeders on fully slatted floors

A study was conducted to evaluate the minimal floor space allowance for gestating sows group-housed in pens with electronic sow feeders (ESF). Five floor space allowances were each tested in 4 pens: 1.5 m², 1.7 m², 1.9 m², 2.1 m² per sow, and 1.5 m² per sow with more space (2.1 m² per sow) during the first week of mixing (2.1/1.5 m²). The floor space allowances were achieved by adjusting pen size (from 80 to 88 m²) and group size (42, 46, and 51 sows per pen). Pregnant sows (n = 928, Large White × Landrace, parity = 1 to 9) were moved to ESF pens at about 5 wk of gestation and remained in their pens until about day 109 of gestation. Sows farrowed in individual stalls and weaned their litters at about 19 d after farrowing. Sows that were rebred within 1 wk after weaning were considered to have completed the study. Performance, skin lesions, and incidence of lameness in ESF pens were monitored for all sows. Data were analyzed using the Frequency, Glimmix, and Mixed procedures of the SAS software. Floor space allowance did not affect (P = 0.18 or greater) body weight, backfat depth, or condition score in ESF pens or during the lactation period. No differences (P = 0.23 or greater) were detected in farrowing rates (95, 92, 94, 94, and 95% for 1.5, 1.7, 1.9, 2.1, and 1.5/2.1 m², respectively), completion rates (83, 79, 80, 86, and 86%), live litter size farrowed (12.5, 12.7, 12.2, 12.3, and 12.5 pigs per litter, SE = 0.24), litter size weaned (10.4, 10.5, 10.2, 10.2, and 10.6 pigs per litter, SE = 0.22), litter weight farrowed, litter weight weaned, or wean-to-estrus interval among treatment groups. Skin lesion scores for the body and for the vulva 2 d after mixing into ESF pens and when moved from ESF pens to farrowing quarters were similar across treatment groups (P = 0.54 or greater). Incidence of lameness 2 d after mixing was higher (χ2 = 21.1, df = 4; P = 0.01) for sows allowed 2.1/1.5 m² (9.5%) and 2.1 m² (4.2%) than sows allowed 1.9 m² (1.8%), 1.7 m² (2.9%), and 1.5 m² (1.5%), which may be associated with fighting to establish dominance hierarchy during mixing in pens with larger open areas. No difference was observed in incidence of lameness when moved from ESF pens to farrowing quarters among treatment groups. These results suggest that the minimal floor space allowance of 1.5 m² appears to be acceptable for maintaining reproductive performance and welfare of gestating sows group-housed under conditions of the current study.