Effects of productive lifespan on phenotypic lifetime daily milk yield in dairy cows:conclusions from 20-year herdbook data analysis

Summary

Although the productive lifespan is a key factor for the sustainability of dairy farming, it has decreased in European countries over many years. We aimed to study the development of production level (2.22 million cows) and productive lifespan (2.31 million cows) from 1999 to 2019 by analysing Swiss herdbook data of Holstein cows (from two different herdbooks: HO_HOS from Holstein Switzerland, HO_SHB from swissherdbook), Swiss Fleckvieh (SF), Brown Swiss (BS), Simmental (SI) and Original Braunvieh (OB) breeds, as well as culling reasons (limited to the period from 2008 to 2019, n = 149 033). Average lifetime daily milk yield (LDMY, kg) continuously increased in all breeds studied: in 1999, it ranged from 6.4 ± 3.6 kg/d (SI) to 8.5 ± 4.0 kg/d (HO_HOS), while until 2019, it had significantly increased to values between 7.6 ± 4.1 (SI) and 12.1 ± 5.5 (HO_HOS) kg/d. Contrary to the prevailing European trend, average productive lifespan (PL, years) increased significantly (and stabilised) in all breeds except OB from 1999 to 2019: in 1999, it ranged between 1.9 ± 1.7 (HO_SHB) and 3.5 ± 2.7 years (BS), and increased to a range between 3.0 ± 2.1 (HO_HOS) and 3.8 ± 2.8 years (SF) in 2019. In contrast, PL in OB decreased from 4.6 ± 3.3 to 3.6 ± 2.8 years over the same period. Culling rates until the second lactation ranged from 40% (SF) to 51% (HO_SHB). For specialised dairy breeds, fertility and udder health problems were the main culling reasons, while insufficient milk production was more relevant in the dual-purpose breeds OB and SI. Long-living cows were characterised by a lower average milk yield in first lactations, a slower average milk yield increase across subsequent lactations, lower average somatic cell counts and shorter calving intervals. An increase in LDMY through extended PL was most pronounced in early lactations but persisted beyond the 10th lactation in all breeds. When comparing the development of LDMY over 20 years with differences in LDMY among cows culled at different lactations, it becomes evident that the phenotypic increase in LDMY observed over the past two decades is comparable in magnitude to the increase achievable by extending PL of young cows by approximately two lactations, regardless of the breed considered. We conclude that increasing the proportion of mature cows within the herd could yield substantial improvements in the economic and ecological efficiency of dairy production.