Review: Overview of factors affecting productive lifespan of dairy cows.

The average productive lifespan is approximately 3 to 4 years in countries with high-producing dairy cows. This is much shorter than the natural life expectancy of dairy cattle. Dairy farmers continue to cull cows primarily for reasons related to poor health, failure to conceive or conformation problems prior to culling. These reasons may indicate reduced welfare leading up to culling. Improvements in health care, housing and nutrition will reduce forced culling related to these welfare reasons. However, productive lifespan has remained similar in decades, despite large improvements in cow comfort and genetic selection for the ability to avoid culling. On the other hand, genetic progress for economically important traits is accelerating within the last decade, which should slightly shorten the average economically optimal productive lifespan. A major driver of productive lifespan is the availability of replacement heifers that force cows out when they calve. The average productive lifespan could be extended by reducing the supply of dairy heifers, which would also have benefits for environmental sustainability. Improvements in culling decision support tools would strengthen economically optimal replacement decisions. In conclusion, major factors of the relatively short productive lifespan of dairy cows are welfare-related, but other economic factors like supply of heifers, genetic progress and non-optimal decision-making also play important roles.