Block calving systems see continued uptake

• The proportion of GB farms operating under block calving systems has risen to 21.4%
• Larger dairy farms, tend to operate on a more defined system

Analysis by AHDB utilising BCMS data, shows that the share of GB farms in 2025 running any type of block calving system has risen to 21.4%, while the number of farms running an all year round (AYR)* system remained relatively steady at around 35%.

The increased adoption of specific calving systems is significant over a longer time period. In 2021, 48.4% of farms were categorised as non-defined* in their calving pattern; in 2025 this had fallen to 43.6%.

Figure 1: Farms by calving type

Source: BCMS, AHDB
Figure 1 is a bar chart showing total farms by calving type from 2021 to 2025.

Block calving systems have risen by 4.8 percentage points since 2021. This movement has exaggerated the peaks and troughs in the seasonal birthing profile of the GB dairy herd.

Within this, Autumn and Spring* block calving have been the most popular, accounting for 7.0% and 6.7% of all systems, respectively. From 2024 to 2025, the Spring block system saw the largest increase, moving up by 1.3 percentage points, potentially adding to processing capacity challenges in the spring peak of milk supplies.

Meanwhile, Autumn block saw a marginal decline of 0.1% over the same time period.

Autumn block calving systems are typically more expensive to operate and require incentivisation with adequate seasonality milk pricing, particularly considering inflated input costs.

Figure 2: GB monthly births to dairy dams

Source: BCMS

Figure 2 is a line graph showing the number of calves registered each month to dairy dams in Great Britain, from 2023 to 2025.

Larger dairy farms, in terms of number of births per year, tend to operate on a more defined system. In 2025, just 8.7% of the largest farms (calving over 500 a year) ran a ‘non-defined, calving system’, favouring an AYR calving pattern (64.1%), unchanged from 2024. In comparison, 57.7% of the smallest farms (calving less than 200 a year) had a ‘non-defined’ calving system.

Farms with between 200–500 births per year, see a more mixed approach to operating systems with 47.2% AYR, 28.6% block and 24.2% non-defined.

The number of larger farms has been increasing over recent years and hold a greater share of the national milking herd. Meanwhile, the smallest farms continue to decline, supporting the shift to AYR and block systems. This trend will be considered when forecasting the future of milk supplies.

Figure 3: 2025 operating system by farm size (births per year)

Source: BCMS, AHDB

Figure 3 is a bar chart showing operating system by farm size (births per year) in 2025. Defined systems are more common with farms with between 200–500 births per year.

*Definitions for analysis

2020 was the first time we were able to see the breakdown based on calf registrations for each farm in the country. Historically, the breakdown of system in GB has been based on farmers’ self-assessment of which system they believe they operate.

The data excludes any farms where all registrations were for non-dairy calves, and also excludes farms who had less than 25 calf registrations in the year. Our farm key performance indicators suggest block calving herds should target 85% of calvings within a 6-week window, although the 'good' level is set at between 70–85%. For this analysis we have used a wider definition of 4 months and 80% of registrations as set out below:

• Spring block: 80% of registrations occur within 4 months from 1 Feb to 31 May
• Autumn block: 80% of registrations occur within 4 months from 1 Aug to 30 Nov or 1 Sep to 31 Dec
• Other block: 80% of registrations occur within 4 months other than defined in spring or autumn block
• Dual block: 90% of registrations occur within the spring block or autumn block windows defined above.
• AYR: Registrations are spread relatively evenly throughout the year, but that can be based on a 12-month, 11-month or 10-month calving system. 12-month means each month sees 3.3–13.3% of annual registrations. 11-month means 4.1–14.1% of annual registrations in 11 months of the year, and 10-month means 5–15% of annual registrations in 10 months of the year.
• Non-defined: covers any farm not falling into one of the other categories.

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