Prevalence of lameness in sheep transported to meat processing plants in New Zealand and associated risk factors

Abstract

ABSTRACTAims: To estimate the prevalence of lameness in sheep transported to meat processing plants in New Zealand, and to identify factors associated with the prevalence of lameness.Methods: The survey was conducted over the main meat processing season, running from October 2012 to the end of May 2013, at 10 sheep processing premises (five North Island and five South Island). A sample of 50 sheep selected from approximately six sheep consignments per week from each of the processing plants were scored for lameness, using a scale from Grade 1 (mild) to 3 (severe, non-weight-bearing). For each consignment the breed, age class and mean carcass weight were recorded. A multivariable regression model was fitted to identify the risk factors for prevalence of lame sheep (Grade 1–3) within a consignment.Results: In total, 1,854/78,833 (2.4 (95% CI = 2.2–2.5)%) sheep were diagnosed with lameness. Of the 1,854 lame sheep, lameness severity was Grade 1 in 1,349 (72.8%), Grade 2 in 450 (24.3%) and Grade 3 in 55 (3.0%) sheep. Within consignments ≥1 lame sheep was observed in 600/1,682 (35.7 (95% CI = 33.4–38.0)%) consignments. In Merino lambs and ewes the prevalence of lameness was greater than that of other breeds (p < 0.001), but in rams/wethers, the prevalence of lameness was lower in Merino than other breeds (p < 0.05). In sheep originating from the North Island, increasing mean carcass weight was associated with an increase in the prevalence of lameness (p < 0.001), but in the South Island prevalence was similar for different carcass weights (p = 0.5). In the North Island increasing yarding time was associated with an increase in the lameness prevalence (p < 0.01), but not in the South Island (p = 0.7). Sheep from the South Island generally had a higher prevalence of lameness than the North Island and the prevalence of lameness was lower over summer and autumn relative to the previous spring (p < 0.01).Conclusion: The results from this survey provided a measure of the prevalence of lameness in a section of the New Zealand sheep population, namely those animals sent for slaughter; as well as identification of several risk factors associated with lameness.