Pressure load on specific body areas of gestating sows lying on rubber mats with different softness

Rubber mats offer a possibility to increase lying comfort for sows with positive effects on sows lying behavior and health. However, until now there is no information about the relationship between softness of rubber mats and pressure load on certain body areas of sows. We used a total of 68 (40 multiparous, 28 primiparous) German Landrace x German Landrace sows with a body weight within the range of 90 to 330 kg (divided in 3 weight classes) in order to measure peak force and distribution of pressure during lying in sternal and half recumbent position. Measures were done in an experimental pen that was equipped with a pressure sensor map system (5400 NTL; Tekscan Inc., Boston, MA). Three rubber mats differing in softness (penetration depth: hard mat: 4.0 mm (HM), soft mat: 14.6 mm (SM), very soft mat: 43.0 mm (VSM)), were tested and compared to concrete floor (C) as a reference. Pressure load was analyzed in sternal position for body regions sternum, belly and ham, and in half recumbent position additionally for shoulder. For each lying position we determined the body region with the highest pressure load and analyzed the peak force (PF) and the contact area (CA) using a mixed model ANOVA (MIXED Procedure of SAS Enterprise, version 4.3., SAS Institute Inc., Cary, NC) with floor type, weight class of sows and their interaction as fixed factors. Overall, the highest values for PF in sternal position were found on the sternum (median: 1.62 N/cm2) and in half recumbent position on the shoulder (median: 2.72 N/cm2). In sternal position PF on the sternum was lower on VSM compared to C (P = 0.001). In half recumbent position PF on the shoulder was lower on VSM compared to C (P = 0.013) and compared to HM (P = 0.011). Weight of sows affected PF on the sternum in sternal position with lower values in weight class 1 compared to weight class 2 (P = 0.001) and weight class 3 (P = 0.002). CA under the sternum was larger on SM (P = 0.016) and VSM (P = 0.008) compared to C in sternal position and this was affected by weight class (P = 0.0002). In half recumbent position floor type did not affect CA under the shoulder but CA was larger in weight class 2 and 3 compared to weight class 1 (all P < 0.05). Assuming that a reduced peak force in combination with pressure distributed over a larger area will increase lying comfort, hard rubber mats do not seem to offer a high lying comfort with regard to pressure load on debited body regions such as sternum or shoulder.