An SRB cow stands and licks her newborn calf in a calving box.

Extended lactations in multiparous dairy cows

News published: 23/10/2025

The aim of this project was to investigate the effect of extended calving intervals on fertility, milk production, and culling in the second lactation, as well as the relationship between calving intervals, milk yield in the second lactation, and cow mortality during the first month after calving.

Licentiate lecture

Annica Hansson will defend her licentiate thesis “Extended lactations in multiparous dairy cows” on October 24 at 9:15 a.m. in Room L, Undervisningshuset, Ultuna campus.

The lecture can also be followed digitally via Zoom.

More information

Traditionally, Swedish dairy producers have aimed for a calving interval of 12–13 months, meaning that each cow calves once per year. As milk yields has increased over time, interest in extended calving intervals has grown. For many farmers, drying off high-yielding cows is a challenge, and statistics show that the highest risk of disease and mortality occurs around calving. A longer interval between calvings, may potentially reduce the number of health problems for the cow.

Earlier studies have shown that first-parity cows are particularly suited for longer lactations, since they typically have a more even milk production level over time. In this study, we instead focused on second-parity cows, which have an overall higher milk yield but a more rapid decline of the milk production in the later stages of lactation. The study was carried out in 12 high-yielding herds with different production conditions, including feeding strategies, conventional or automatic milking systems, and two or three milkings per day.

Cows were either inseminated about 50 or 140 days after calving. The results showed that cows with a longer waiting period before insemination, and thereby longer calving interval, had better fertility outcomes. The results suggest that cows with a longer waiting period, and thus recovery period, before insemination can be beneficial. Milk production between two calvings was not affected by the length of the calving interval.

Data from the Swedish official milk recording system over a seven-year period were analysed in a second, retrospective study. These results showed that the risk of mortality after calving increased for cows with longer calving intervals. However, this association was not found in the subset of the highest-yielding herds. The results of such retrospective studies should be interpreted with caution, since a cow may have received a longer calving interval for other reasons, such as illness or reduced fertility, which in turn could have affected the mortality risk.

In summary, the findings suggest that longer calving intervals can be a valuable alternative to the traditional 12-month cycle, particularly in highyielding herds. At the same time, our analyses of historical data show an association between longer calving intervals and a higher risk of mortality around calving.