A systematic review and meta-analysis of lameness scoring methods and the prevalence of lameness of dairy cows in Northwest Europe

Lameness in dairy cows, linked to claw disorders and pain, is a major welfare concern. Studies worldwide use various scoring methods, resulting in differing prevalences. To address this, we developed a 3-level comparative locomotion scale (Welfare Quality equivalent [WQE]), to compare studies using different lameness scoring methods and provide insights into the distribution of lameness prevalence. This scale defines lameness and severe lameness according to stride length, weightbearing and back posture. To account for different locomotion scales used, we created 2 versions, with the main difference being the threshold for lameness. According to a "conservative" version of the scale, no irregularities are allowed in a normal gait, lameness is defined as any irregularities in the gait and severe lameness as: shortened strides, (strong) reluctance to bear weight ≥1 limb and an arched back standing and walking. According to a "lenient" version, some slight irregularities are allowed in a normal gait; lameness is defined as: shortened strides, unequal weightbearing, and arched back walking/standing; and severe lameness as: shortened strides, (strong) reluctance to bear weight ≥1 limb and arched back standing and walking. We also aimed to describe the prevalence of lameness by using meta-analysis, and to inventory risk factors associated with lameness. We identified 53 studies on lameness prevalence from SCOPUS and Web of Science, focusing on Northwest Europe over the last 25 years. Other eligibility criteria included scoring of cows by trained assessors and criteria relating to housing and methodology. We found that cow-level prevalence of lameness reported by studies ranged from 2.6% to 63.7% (with a median of 29.5%). A random effects model was used to analyze lameness distribution based on the WQE scale and to estimate weighted average lameness prevalences. The estimated mean prevalences were 28% (95% CI 23%-33%) for the lenient definition of lameness, 23% (95% CI 18%-29%) for the conservative definition of severe lameness, and 9% (95% CI 5%-12%) for the lenient definitions of severe lameness. The estimated prevalence of the conservative definition of lameness was extremely variable. Subgroup analyses were performed to explain the high heterogeneity between studies. Although some unexplained heterogeneity remained, lameness prevalence estimates differed between country and were lower in pasture access subgroups. Finally, we reviewed risk factors for lameness in Northwest Europe, based on 38 studies. Key risk factors for lameness included lack of pasture access, concrete floors, lying surfaces other than deep bedding, poor body condition and higher parity. This meta-analysis revealed significant variability in lameness prevalence across studies using different lameness scoring methods. Sparse herd information and vague lameness scoring descriptions complicated interpretation and WQE scale development. Our findings highlight the need for more randomized controlled trials investigating risk factors, and standardized, large-scale observational lameness prevalence research with detailed reporting. Furthermore, our results suggest that reduction of lameness prevalence is possible through providing pasture access, optimizing housing and other management interventions. We recommend using the WQE scale or an equivalent standard scale to obtain comparable scores and prevalences.