Reasons and risk factors for on-farm mortality in Estonian dairy herds

Mortality of dairy cattle causes financial loss for the farmer and reflects animal welfare status. The aim of this study was to determine the on-farm mortality (unassisted death and euthanasia), reasons, as well as risk factors for on-farm mortality in Estonian dairy cattle. Data of years 2013 and 2014 about all cattle from dairy herds in Estonia was collected from the Estonian Agricultural Registers and Information Board. The dataset included records of 363,380 animals from 2616 herds. Multivariable Weibull proportional hazard models with herd as random effect were composed for detecting significant associations between potential risk factors and on-farm mortality (composed outcome including unassisted death and euthanasia). Data from Estonian Livestock Performance Recording Ltd was used to determine the reasons for on-farm mortality.The overall mortality rate (MR) including unassisted death and euthanasia was 6.95 per 100 animal-years. Mortality was highest in male (MR=55.96 per 100 animal-years, 95% CI 54.53; 57.42) and female (MR=27.70 per 100 animal-years, 95% CI 26.99; 28.43) calves up to three months old and lowest in female cattle aged 12–18 months (MR=0.99 per 100 animal-years, 95% CI 0.89; 1.10). The main farmers´ stated reasons for dairy cow mortality were ‘Metabolic and digestive disorders’ and ‘Feet/claw disorders’. The main reasons for on-farm mortality among youngstock were ‘Metabolic and digestive disorders’, ‘Respiratory and infectious diseases’ and ‘Other reasons’. The risk factor analysis was carried out in three age categories: <3 months, 3–23 months and ≥24 months. Estonian Holstein breed was associated with significantly higher risk of mortality compared to Estonian Red breed cattle in every age group. The hazard of on-farm mortality was significantly higher for herds with over 400 animal-years compared to smaller herds in all age groups. Regional differences in mortality hazard were present in the model of youngstock over 3 months and adult cattle. Seasonal differences in mortality rate were present and differed by age groups.This is the first study revealing the on-farm mortality and related risk factors in Estonian dairy cattle population.