Factors affecting posture-changing in loose-housed and confined gestating sows
The time taken to lie down and stand up was determined for dry sows from different housing systems and related to physical and genetic parameters. In experiment 1, the times taken to lie down by 32 sows in two dry-sow housing conditions were measured. Sows housed long-term in stalls took longer to lie down than group-housed sows (20.42 v. 9.28 s, P < 0.001). Group-housed sows took longer to lie down in the open than to lie down against a wall (11.07 v. 7.48 s, P = 0.004). The length of time taken for stall-housed sows to lie down had strongest association with body length (P = 0.033, R2 = 0.718). The length of time taken for group-housed sows to lie down in the open had strongest association with the proportional weight of the extensor carpi radialis, (P = 0.001, R2 = 0.915). In experiment 2, the times taken for 30 sows in stalls to lie down and stand up were measured and genotype differences investigated. There were no differences between genotypes in total times taken to stand up or lie down, but total times taken to stand up quickly and lie down had strongest association with body length (P = 0.032, R2 = 0.185, and P < 0.001, R2 = 0.574 respectively). The results indicate that sows housed long-term in gestation stalls experience difficulty of movement when standing up quickly and lying down. Although the chronic effects of lack of exercise and the acute effects of floor type may contribute to this difficulty, the major factor is likely to be space restriction as the times taken to lie down and stand up quickly both increase as body length, and hence dynamic space requirement, increases. Lying down in an unrestricted environment is under muscular control and the degree of control depends on the proportion of muscle weight to total body weight. The factors affecting lying down and standing up should be considered when designing dry-sow and farrowing accommodation.