Effect of locomotion score on sows’ performances in a feed reward collection test

Abstract

Sows housed in groups have to move through their pen to fulfil their behavioural and physiological needs such as feeding and resting. In addition to causing pain and discomfort, lameness may restrict the ability of sows to fulfil such needs. The aim of our study was to investigate the extent to which the mobility of sows is affected by different degrees of lameness. Mobility was measured as the sow's willingness or capability to cover distances. Feed-restricted hybrid sows with different gait scores were subjected to a feed reward collection test in which they had to walk distances to obtain subsequent rewards. In all, 29 grouphoused sows at similar gestation stage (day 96.6 ± 7 s.d.) were visually recorded for gait and classified as non-lame, mildly lame, moderately lame or severely lame. All sows received 2.6 kg of standard commercial gestation feed per day. The test arena consisted of two feeding locations separated from each other by a Y-shaped middle barrier. Feed rewards were presented at the two feeders in turn, using both light and sound cues to signal the availability of a new feed reward. Sows were individually trained during 5 non-consecutive days for 10 min/day with increasing barrier length (range: 0 to 3.5 m) each day. After training, sows were individually tested once per day on 3 non-consecutive days with the maximum barrier length such that they had to cover 9.3 m to walk from one feeder to the other. The outcome variable was the number of rewards collected in a 15-min time span. Non-lame and mildly lame sows obtained more rewards than moderately lame and severely lame sows ( P < 0.01). However, no significant difference was found between non-lame and mildly lame sows ( P = 0.69), nor between moderately lame and severely lame sows ( P = 1.00). This feed reward collection test indicates that both moderately lame and severely lame sows are limited in their combined ability and willingness to walk, but did not reveal an effect of mild lameness on mobility. These findings suggest that moderately and more severely lame sows, but not mildly lame sows, might suffer from reduced access to valuable resources in group housing systems.

Locomotion Disorders and Skin and Claw Lesions in Gestating Sows Housed in Dynamic versus Static Groups

“…For lameness, no unequivocal cut-off between “lame” and “non-lame” can yet be determined, as some authors consider that some changes in the locomotion pattern (e.g., stiffness) might not result in discomfort or pain [ 66 ; 68 ] and therefore should not be considered as lame. In the present study we used a cut-off based on the lameness score at which sows became less willing to walk to obtain a highly tempting reward [ 45 ]. Using the mean locomotion score allowed us to describe the severity of lameness in a more nuanced way than classifying sows simply as lame vs. non-lame.…”

“…Locomotion of sows was analyzed as mean locomotion score, lameness prevalence and lameness incidence. For estimating lameness prevalence, sows were considered lame when their locomotion score was >60 mm on the tVAS [ 45 ]. For estimating lameness incidence, a new case of lameness was defined as a previously non-lame sow (<60mm on tVAS) that had become lame (>60mm) and for which the locomotion score had increased by >30 mm since the previous score.…”

A Review of Pain Assessment in Pigs

“…Subjective scores are prone to poor reliability (125), and one study showed poorer interobserver agreement at the lower end of the lameness scale (126). For example, no difference in motivation to obtain a food reward was detected between mildly lame and non-lame sows (113). However, it is possible that pigs may conceal signs of mild pain more easily than signs of severe lameness-pain, which could be advantageous in relation to access to resources.…”

“…Food consumption decreased after thoracotomy surgery in pigs (110), and time spent feeding has been used to assess the efficacy of pain mitigation strategies in pigs undergoing abdominal surgery (111) and a femoral fracture model (112). In a study using a feed reward collection test to assess sows’ motivation to obtain feed rewards with different levels of lameness, moderately and severely lame sows obtained fewer rewards than mildly and non-lame sows (113). Unexpectedly, tail-bitten pigs, which had been given ketoprofen, spent less time at the feeder compared with those given a saline placebo (114).…”

“…A recent study using lame sows trained to retrieve food rewards (113) and another study investigating how long castrated piglets take to navigate a handling chute (105) go some way to investigating a motivational trade-off in relation to pain. This approach could be investigated further in pigs, adapting examples of behavioral tests used in rodent models of pain, such as the place escape/avoidance paradigm (PEAP) (17), the “Escape test” (199), or the facial reward/conflict paradigm (200).…”