Repeatability of a lameness scoring system for finishing pigs

LAMENESS is a major cause of concern in many livestock species. For example, studies in finishing pigs have demonstrated an overall prevalence of foot lesions of 93-8 per cent (Mouttotou and others 1998) and of adventitious bursitis of 51 per cent (Mouttotou and others 1999). The welfare significance and relationship to lameness of these conditions is not known, although a recent study by Mouttotou and Green (1999) has demonstrated that piglets with sole erosions and skin abrasions spent more time lying and less time on activities such as standing, walking, playing and fighting. The objective of this study was to design a simple, repeatable scoring system to quantify lameness (without reference to potential causes) that could be used for clinical or research investigations. Observing and recording the level of lameness within a herd could be used as a clinical tool for monitoring a lameness problem on a unit and producing evidence of active disease management for farm assurance schemes. In addition, a reliable scoring system could be used in epidemiological studies for identification of potential causal factors of lameness. Lameness scoring systems based on simple descriptive numerical scales have been designed for many species. Kestin and others (1992), Manson and Leaver (1988) and Welsh and others ( 1993) have produced scoring systems for broilers, cattle and sheep, respectively, based on observing gait abnormalities during movement. An equivalent scoring system has not been developed for pigs. This study examined lameness within a single herd of 600 growing and finishing pigs (bodyweight between 40 and 100 kg). The pigs were housed on partially slatted concrete floors, in groups of 12 to 18 and fed a liquid whey-based ration. All pigs were observed both in their pens and in a walkway (7 x m) immediately adjacent to the home pens. Any pig that was considered lame was identified so that the farmer could administer appropriate treatments and nursing care. A scoring system (Table 1) was developed by observing the behaviour, standing posture and gait of pigs while they were undisturbed and during exit into an unfamiliar environment. Using observations of each attribute, a score was assigned based on a six-point numerical scale where a score of 0 represented no abnormality in posture, gait, or behaviour, and 5 represented a severely lame pig, incapable of standing unaided. Each level had defining criteria (identified in bold type in Table 1), such as 'uneven standing posture' which were necessary for a specific score to be attributed. Other criteria, such as 'apprehension of boisterous pigs', were considered to be useful supporting evidence. The level of agreement between the scores attributed by various observers was analysed using the kappa statistic (Intercooled Stata 5.0; Stata Corporation) which is a measure of agreement that corrects for the probability that the observers agree by chance. The kappa statistic is a quotient that can take values from 0 (no agreement beyond chance) to 1 (perfect agreement), where 0*4 to 0 5 is considered to be moderate agreement beyond chance. Levels below this indicate that a test has poor specificity and/or sensitivity (Martin and others 1987). Two observers (Fl and F2) familiar with the scoring system independently evaluated the lameness score of 201 randomly selected pigs. There was a high level of agreement (94 per cent) and the associated kappa statistic (0.90) was high indicating very good agreement beyond that expected by chance between these two observers (Table 2). The distribution of scores attributed by observers F1 and F2 to the random selection of 201 pigs is shown in Fig 1. In a separate study, seven undergraduate veterinary students (U1 to U7), previously unfamiliar with the scoring