Evaluation of Floor Space Allowance for Group-Housed Gestating Sows: Application of Allometric Principles

Floor space allowances for young pigs are determined using allometric principles and change with body weight of the pig. In contrast, recommended floor space allowances for breeding sows are static and expressed on per sow basis without consideration of variation in sow BW. The objective of this study was to evaluate floor space allowances using allometric principles. Gestating sows (n = 760, parity 1 to 9) group-housed in pens with electronic sow feeders (ESF) were used. Four floor space allowances (1.5, 1.7, 1.9, and 2.04 m²/sow) were evaluated in four pens (42 to 51 sows/pen) over a period of 18 months. Sows were moved to pens 5 wk after mating and remained there until d 109 of gestation when moved to farrowing quarters. The following data were recorded: total duration of fighting among sows immediately after mixing, d 2 and d 7 after mixing in pens, skin lesions and salivary cortisol concentrations d 2 after mixing and before moving for farrowing, lateral and sternal lying during wk 3 and wk 9 after entering pens, BW change in pens, and farrowing performance. The k-value was calculated for sows in each pen using individual body weight at entering pens. Average weight for sows in each pen across floor space treatments ranged from 196 to 223 kg at entering pens. The k-value was 0.044 to 0.046, 0.047 to 0.051, 0.054 to 0.057, and 0.059 to 0.062 for 1.5 m², 1.7 m², 1.9 m² and 2.04 m² of floor space allowance, respectively. These results indicate that the k-value varied from 0.002 to 0.004 within the same floor space allowance treatment, depending on body weight of sows in the pen. There was no correlation between the k-value and any variable of sows that were measured (all R² <0.16, all P > 0.13), suggesting that increasing k-value from 0.044 to 0.062 did not affect sow performance and welfare. Across floor space treatments, total duration of fighting at mixing was 32 sec/sow/2 h, farrowing rate 93.7%, litter size farrowed live 12.4 and weaned 10.4. The minimal floor space allowance for gestating sows group-housed under conditions of the current study may be calculated using the equation: A (m²/sow) = 0.044 BW^0.66, where A is area in m² and BW is body weight in kg. The k-value of 0.044 derived from this study needs further research for validation and it may change under different conditions from the current study.