Mortality trends in Finnish dairy cow herds during 2011 - 2020

In many European countries, like in Finland, dairy herd sizes have been increasing. Additionally, many producers are switching from conventional parlor milking to automatic milking systems and from other breeds to Holstein cow herds. At the same time, mortality of cows has increased. To gain information of the factors affecting cow mortality in vital, actively operating dairy herds, we studied Finnish herds that had uninterrupted Dairy Herd Improvement data recording during 2011-2020 and had continued production for at least one full year after that (n = 3 179). We explored the change in annual herd level incidences of several parameters of mortality and lifetime milk yields and studied their associations with herd size and proportion of Holstein cows in the herd using generalized linear models with repeated measurements. Overall mortality (euthanised + unassisted deaths) risk first slightly decreased, but then steadily increased from 5.6% in 2013 to 6.9% in 2020, being statistically significantly higher in larger compared to smaller herds and in herds with high proportions of Holstein cows. The increase in overall mortality was due to an increase (from 3.8% to 5.0%) in the proportion of euthanised cows, significantly affected by increase in Holstein cows in herds, whereas the proportion of unassisted deaths remained quite stable (below 2%). However, the average culling % decreased from 33% to 30%, age of culled cows slightly increased, and lifetime milk yields of the cows linearly increased during the study period. Our results suggest that structural changes within dairy industry are associated with mortality, through the effects they have on herd size and breed of cows.