The ability to detect lameness in sows using a motivation test

Even though group housing implies higher welfare standards than gestation crates, it sometimes impairs welfare of sows. Lameness is one of the main problems. Motivation tests are used to measure animals’ willingness to work for a reward, e.g. feed. Perhaps motivation tests could also be used to detect lameness if the type of work for the reward involves locomotion. The objective of this study was to investigate the impact of lameness on the ability to cover distances for food rewards. Twenty-nine hybrid sows were used. They were fed restrictedly (2.6 kg commercial gestation diet, daily). Sows were habituated and trained for 5 days in an experimental pen with two feeding locations. They were trained daily for 15 minutes, after scoring locomotion and classifying them as non-lame, mildly-lame or lame. Both a light and sound cue was used to indicate an available reward. Sows had to walk around a Y-shaped fence separating both feeders in order to obtain successive rewards. Training was considered successful when sows obtained at least four food rewards. After completion of training, sows were tested individually, once per day on three non-consecutive days. The effect of lameness on willingness to work for rewards was analysed using a Poisson model with gestation stage, parity and body weight as fixed effects. The willingness to cover distances for food rewards differed (P=0.006) between lame sows (mean=4.07 SEM=0.41) vs. non/mildly-lame sows, but not (P=0.479) between non-lame (mean=10.76, SEM=0.98) and mildly-lame sows (mean=11.75, SEM=1.65). These findings suggest that either the locomotion ability is not strongly reduced in sows with a mild degree of lameness, and/or that the present motivation test, although sufficiently sensitive to detect truly lame sows, may not be sensitive enough to detect mildly-lame sows. Sensitivity could possibly be improved by increasing the workload or reducing the attractiveness of reward.