Extended lactation study

The farmlet study measures production and the balance between feed supply and demand to estimate overall system profitability. Data from a nearby commercial farm is also being used to provide insight into how the system affects workload throughout the year.

The system concept was developed in 2023 through our Frontier Farms programme. This programme aims to identify competitive risks and opportunities and worked with farmers to design and test new novel farm systems. The co-design team selected extended lactation as an option to investigate because it looked most promising for reducing workload peaks while maintaining profitability with the aim of mitigating risks around labour availability and flexibility.

The investigation began with a modelling exercise. Profitability was predicted to be higher in Northland, similar in Waikato, and slightly lower in the South Island for a 24-month calving interval with half the herd calving each spring, relative to a system with 12-month calving intervals. This system progressed to testing at a farmlet scale, and the calving pattern is shown below.

Eighteen-month calving intervals were also modelled but were considered more difficult to manage, with calving shifting between spring and autumn and pasture supply not always matching herd demand - milk production may be higher, but profit was predicted to fall due to extra feed requirements.

Positive benefits

In June 2025, the focus of the study changed to improve the sector’s understanding of solutions and strategies for bobby calves. The study expanded to demonstrate the extended lactation system in separate Friesian and Jersey farmlets, which also enables an understanding of likely crossbreed performance.

A 24-month calving interval reduces the typical 22% replacement rate to 11%, which could potentially age the herd considerably. To keep a balanced age structure in the Extended Lactation (EL) farmlet, one-third of the half of the herd calving each year, are first calvers. This results in an effective replacement rate of 17%.

With fewer calvings and a lower effective replacement rate, this means non-replacement calves are nearly 60% lower than an annual system, making it easier to rear the remaining calves as dairy-beef. The difference is such that at a national scale, all non-replacement calves could be reared and finished within existing land and feed capacity used for dairy-beef.

The Control-Friesian Farmlet - consists of 42 cows on 15 ha, subdivided into 30 x 0.5 ha paddocks (2.8 cows/ha). The Control-Jersey farmlet consists of 25 cows on 7.5 ha, subdivided into 15 x 0.5 ha paddocks (3.3 cows/ha). Both are equivalent to 1400 kg liveweight/ha. All cows calve annually in spring.

The Extended lactation-Friesian farmlet consists of 84 cows on 30 ha, subdivided into 60 x 0.5 ha paddocks (2.8 cows/ha). Approximately half of the cows are deliberately not mated each year, and thus half calve each spring.

The Extended lactation-Jersey farmlet consists of 50 cows on 15 ha, subdivided into 30 x 0.5 ha paddocks (3.3 cows/ha). Approximately half of the cows are deliberately not mated each year, and thus half calve each spring.

24-month calving interval results to date

The farmlet study has completed two seasons where milksolids production, operating profit, and sustainability were similar to the control group . Read more on ResearchGate.

Performance of control and extended lactation (EL) Friesian farmlets across two seasons 23/24 and 24/25

During the first winter, the extended lactation farmlet needed an extra 180kg of dry matter of extra feed per cow, as half of the herd continued to milk through winter. In an attempt to reduce supplement for the following season, autumn pasture cover was increased, and calving was delayed. However, extra supplements were still needed, and the later calving meant fewer days in milk, lowering production and profit. The farmlet has since returned to the same calving date as control, with extra winter feed planned.

Commercial farm comparison

After promising results in the farmlet trial, a commercial farm volunteered to pilot the system starting in June 2025 to better understand how extended lactation affects farm teams, something a farmlet trial can’t fully capture. Read more on ResearchGate.

Keen to learn more?

If you are interested in this study or would like to learn more about extended lactation, you can contact the project lead Lydia Farrell. You can also sign up to the weekly email updates to follow progress and early findings from the project. Lydia is enjoying working on this newly broken field of research and is motivated to produce practical options for farmers. “My role is to try and see how adoptable an idea is, how it would work in practice and how it might affect farm profitability,”