Dystocia mortality incidence in lambs from Australia and New Zealand

Introduction: Dystocia is an important contributor to lamb mortality. Most studies that include lamb necropsies report cause of death using proportional mortality (expressed as a proportion of necropsies) rather than mortality incidence (expressed as proportion of lambs born). Understanding dystocia mortality incidence will inform research priorities to address the impact of dystocia.

Research objective: To collate and analyse existing data to determine the incidence of dystocia mortality in lambs and inform future research and extension priorities for improving lamb survival.

Method: Meta-analyses of lamb necropsy data from studies conducted in Australia and New Zealand since 2000. We analysed more than 46,000 lambing records involving 8228 lamb deaths and 6225 lamb necropsies using random effects models with a restricted maximum likelihood estimator to estimate pooled proportional dystocia mortality ratios and weighted summary dystocia mortality incidence (pooled and separately for each birth type).

Results: Dystocia mortality incidence (weighted summary proportion of lamb births) was 10% (95% confidence interval (CI): 8, 12) with very high heterogeneity between farms/studies (I²=98.3%). Dystocia mortality incidence was higher for triplet-born/higher-order-multiples (15%; 95% CI 11, 19) than twin-born (7%; 95% CI 5, 8) and single-born lambs (7%; 95% CI 5, 8). Dystocia proportional mortality (weighted summary proportion of necropsies) was 45% (95% CI 40, 49) with high heterogeneity (I²=92.8%) which was consistent with previous reviews. Multiple-born lambs are at similar or increased risk of dying from dystocia compared to single-born lambs.

Conclusion: Strategies to reduce dystocia impact and improve lamb survival should address risk factors for dystocia in all birth types.

© 2025 The Authors. © 2025 Australian Veterinary Association.