Performance of raters to assess locomotion in dairy cows

In lameness research, five-level locomotion scores are used. The objective of this study was to determine the performance of raters to assess locomotion in dairy cows and to study relations between five traits (arched back, asymmetric gait, head bobbing, reluctance to bear weight and tracking up) and locomotion in dairy cows. Locomotion and traits were scored on a five-level ordinal scale. Ten experienced raters scored 58 video records of different cows in two scoring sessions. Intrarater and interrater reliability and agreement were calculated as weighted kappa coefficient (¿w), percentage of agreement (PA) and specific agreement for individual levels of the scale (SA). The relation between locomotion score and traits was estimated by a logistic regression aiming to calculate the size of the fixed effects on the probability of scoring a cow in one of the five levels of the scale. Intrarater reliability ranged from ¿w=0.63-0.86 whereas intrarater agreement ranged from PA=60.3-82.8%. Interrater reliability ranged from ¿w=0.28-0.84 and interrater agreement ranged from PA=22.6-81.8%. The intrarater SA were 76.4% for level 1, 68.5% for level 2, 65.0% for level 3, 77.2% for level 4 and 80% for level 5. Interrater SA were 64.7% for level 1, 57.5% for level 2, 50.8% for level 3, 60.0% for level 4, and 45.2% for level 5. All traits were significantly related to locomotion, being the most important reluctance to bear weight, asymmetric gait and arched back. Interactions between rater and session, and rater and tracking up were significant. In conclusion, experienced raters showed a variable performance to assess locomotion and locomotion traits in dairy cows. Variability of raters should be considered for on-farm utilization of locomotion scoring.