A group of dairy calves around the same age

Block Calving Systems

What is block calving?

Dairy cows in a milking parlour
All cows are dried off at the same time.

Block calving,1 is when cows in a herd only calve during a specific period of time. This is usually a block of 6 to 12 weeks, but can be longer. Some producers have a single calving block in a year, others have two blocks, usually one in spring, and one in autumn. All cows in the herd reach peak milk yield around the same time and the whole herd is dried off together.

In the UK, only about 20% of dairy producers are block calvers, with the remaining 80% calving all year round (AYR).2 In other parts of the world, seasonal calving is more popular. For example, in Ireland, most producers favour block calving. Subsequently, calves born outside of these times are usually considered surplus.3 In New Zealand, seasonal block calving is utilised to take advantage of peak grazing times.

Why use this system?

In a block calving system, only one thing happens at a time. This increases efficiency and so allows producers to focus on keeping standards high for each task. Labour is efficiently managed, and seasonal workers can be utilised during especially busy times. More specialised tasks, such as heat detection, are confined to particular times of the year, so extra attention can be given.

Typically, overhead costs in a block system are lower than in AYR systems, with labour savings, simplified calf rearing and easier nutrition management. In the UK, the AHDB found that the cost of production for spring calving systems was 2.4ppl (pence per litre of milk) less than equivalent AYR systems. While that may not seem like a lot, it adds up when the average cow produces 8,000L in a year.4

Block calving also gives producers a predictable schedule and gives a break from the strict timetable of constant milking that AYR systems must stick to.

What are the issues with block calving?

In a block calving system, milk supply varies predictably over the year.
In a block calving system, milk supply varies predictably over the year.

One of the biggest difficulties of this method is keeping everything well managed. To ensure profitability and to keep the system running, everything must be well timed. Ideally, the majority of the herd needs to calve within a period of 6 weeks. This intense period requires labour, infrastructure, and time to be successful.

A herd’s fertility must be high for a block calving system to be successful. As the calving periods, and therefore the service and heat detection periods, are so tight, low fertility can cause significant problems.5 Similarly, problems with the herd, such as disease, can knock timings off dramatically.

Milk buyers tend to promote and incentivise AYR systems. They prefer to have a consistent supply of milk to meet consumer demand. As block calving causes significant fluctuations in milk production, this therefore does not suit every milk contract.

To summarise, block calving might not suit every producer, but it has numerous benefits. These can be both economical and management related. Rigorous management and periods of high intensity work can help to boost standards and profits. Maximising herd fertility will make sure a producer gets the absolute best out of their herd.


  1. Laven, R. 26 – Veterinary Control of Herd Fertility in Pastoral Dairy Herds. in Veterinary Reproduction and Obstetrics (Tenth Edition) (eds. Noakes, D. E., Parkinson, T. J. & England, G. C. W.) 485–492 (W.B. Saunders, 2019). doi:10.1016/B978-0-7020-7233-8.00026-4.
  2. AHDB. Delivering a more competitive industry through optimal dairy systems | AHDB. https://ahdb.org.uk/knowledge-library/delivering-a-more-competitive-industry-through-optimal-dairy-systems (2017).
  3. van Arendonk, J. A. M. & Liinamo, A.-E. Dairy cattle production in Europe. Theriogenology 59, 563–569 (2003).
  4. UK milk yield | AHDB. https://ahdb.org.uk/dairy/uk-milk-yield.