Thermal and Mechanical Nociception Threshold Tests as Objective Tools to Measure Painful and Non-Painful Lameness Phases in Multiparous Sows
The objective of this study was to quantify differences in thermal and mechanical nociception thresholds when sows are in painful and non-painful lameness states. Twelve, clinically healthy, mixed-parity, crossbred sows were used for each of the nociceptive threshold tests. The sow was the experimental unit and a cross-over design with a 2 (left and right hind limb) x 3 (days: D-1, D+1 and D+6) factorial arrangement of treatments were compared. On induction day (D0), 10 mg of amphotericin B were injected in the distal interphalangeal joint space in both claws of one hind limb. All sows served as their own control and treatment. After completion of the first round, sows were given a 7-d rest period and then the round was repeated with the opposite hind limb induced. All data were statistically analyzed using the PROC MIXED procedure in SAS. A P value of ≤ 0.05 was considered to be significant. No differences were observed for sows that had lameness induced in the left- vs. right hind limb for either the thermal (P = 0.68) or mechanical (P = 0.97) threshold tests. There were also no differences between first and second rounds of induction for the thermal (P = 0.18) or mechanical (P= 0.28) threshold tests. For the thermal nociceptive tests, there was a significant difference for the induced limb when comparing D-1 and D+1 (P < .0001), indicating the lame hind limb tolerated less thermal nociception when in a most lame phase. Similarly, mechanical pressure tolerated by the lame hind limb decreased for every landmark (P < 0.05) when comparing D-1 and D+1. Both tools showed a decreased tolerance of mechanical and thermal stimulation when in a most lame phase, indicating potential for limb lameness detection in sows.