Why is longevity an important metric for the modern dairy herd?

Longevity of a dairy herd has become a metric which has started to be investigated in terms of herd performance, due to its impact on the economics and carbon footprint of the herd. It can reflect the health and welfare status of the herd and has role in terms of public perception of the dairy industry. When defined in the dictionary, longevity means having a long existence. The natural lifespan of a dairy cow has been reported to be approximately 20 years (Nowak, 1999); however research has highlighted that it is more like 3.6 lactations (approximately 6 years) in the UK and 2.8 lactations (approximately 5 years) in the USA. This indicates that management decisions are having large impacts on the average productive lifespan of dairy cows, with the removal of cows from a herd due to old age being rare (Fetrow et al, 2006). The age at exit has been decreasing over the past 13 years, as indicated by the data from the NMR 500 herd report 2022 (Hanks and Kossaibati, 2022), where the median lactation number at exit has decreased from 3.9 lactations to 3.6 over the past 13 years. Increasing the longevity of a dairy herd has been promoted as it decreases the requirement for replacement heifers and increases the average herd production level.