On-farm mortality, causes and risk factors in Estonian beef cow-calf herds.

High on-farm mortality is associated with lower financial return of production and poor animal health and welfare. Understanding the reasons for on-farm mortality and related risk factors allows focus on specific prevention measures. This retrospective cohort study used cattle registry data from the years 2013 and 2014, collected from cattle from all Estonian cow-calf beef herds. The dataset contained 78,605 animal records from 1321 farms in total. Including unassisted deaths and euthanasia (2199 in total) the on-farm mortality rate was 2.14 per 100 animal-years. Across all age groups of both sexes the mortality rate (MR) was highest for bull calves up to three months old (MR=7.78 per 100 animal-years, 95% CI 6.97; 8.68) followed by that for heifer calves (MR=6.21 per 100 animal-years, 95% CI 5.49; 7.02). For female cattle the mortality risk declined after three months of age but increased again among animals over 18 months. The reason for death stated by the farmers was analysed for cattle under animal performance testing. Other/unknown reasons, trauma and accidents, as well as metabolic and digestive disorders, formed the three most commonly reported reasons for death in cattle of all age groups. Weibull proportional hazard models with farm frailty effects were applied in three age categories (calves up to three months, youngstock from three to 18 months and cattle aged over 18 months) to identify factors associated with the risk of mortality. Male sex was associated with increased risk of mortality in cattle up to 18 months of age. No difference between breeds was found for cattle up to 18 months of age. Beef cattle breeds rarely represented or dairy breeds (breed category 'Other') had the highest mortality hazard (HR=1.41, 95% CI 1.11; 1.78) compared to Hereford. The hazard of mortality generally increased with herd size for calves, young stock and older bulls. In female cattle over 18 months of age there was no difference in mortality hazard over herd size categories. Herd location was controlled in the models and regional differences in mortality hazard were found. Common to all age groups, calving season was associated with increased risk of mortality.