After two years exploring extended lactation to reduce peak workload and non-replacement calves, the Extended Lactation project has added a commercial farm alongside the existing farmlet trial.
Inside Dairy
3 min read
At DairyNZ’s Scott Farm, Hamilton, researchers have spent two years testing a 24-month calving interval versus the usual 12 months. The farmlet trial has recently expanded, with Jersey herds added, and a commercial farm is also piloting the system.
The concept was flagged for study in a co-design workshop, with farmers and rural professionals keen to smooth peaks in labour demand. The workload over spring was identified as a key pressure point.
Initial modelling suggested that a 24-month calving interval, with half the herd calving each spring, was the most profitable extended lactation system.
Profitability was predicted to be higher in Northland, similar in Waikato, and slightly lower in the South Island than for a 12-month interval. Eighteen-month calving intervals are likely harder to manage, with spring–autumn shifts and pasture not always matching herd demand. Milk production may rise, but profit was predicted to fall due to extra feed requirements.
The farmlet study has tested a 24-month calving interval with Friesians under Waikato conditions. Half the herd calves each spring. After two seasons, milksolids production, operating profit, and sustainability were similar to the control group (see table 1 for the results).
Table 1: Performance of control and extended lactation (EL) farmlets across two seasons.
1 Drought conditions experienced.
2 In spring 2023 both farmlets had a planned start of calving date of 4 July, but in spring 2024 the EL farmlet had a planned start date of 22 July.
3 Excluding conserved pasture made within the production year or carried over from the previous year.
4 It is currently unknown the extent of labour saving, so labour expenses were assumed to be the same between farmlets. Greater repairs, maintenance and depreciation expenses were assumed for EL to reflect the impacts of winter milking and use of a feed pad during wet conditions.
Initially, the extended lactation farmlet needed 180kg of dry matter of extra feed per cow to keep the herd milking through winter. To reduce feed demand in the following season, autumn pasture cover was increased, and calving was delayed. But 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 usual calving date, with extra winter feed now planned.
They noticed their farm manager seemed significantly less stressed during calving.
With a 24-month calving interval, a typical 22% replacement rate is reduced to 11%, potentially aging the herd considerably. To keep a balanced age structure, 33% of the half of the herd that is calving each year are first calvers, making an effective replacement rate of 17%.
With fewer calvings and a lower effective replacement rate, non-replacement calves drop by nearly 60%, making it easier to rear the rest as dairy-beef.
At a national scale, this system could see all non-replacement calves reared and finished within existing land and feed capacity, offering a practical, sustainable pathway for managing non-replacement calves.
Jersey farmlets were added in June 2025 to explore their performance under extended lactation and the potential for crossbreds.
After promising results in the farmlet trial, a commercial farm was sought to pilot the system under everyday conditions. It’s important to see how the system affects farm staff — something a farmlet trial can’t fully capture.
Sharemilkers Ben Fisher, Emma Gardiner and Caleb Higham have transitioned their 240-cow herd at Gordonton to the 24-month calving interval system. They mated only 60% of their crossbred herd in spring 2024 and completed calving in early September 2025.
Ben says the trial is going well, with most cows performing strongly.
“They milked well through the winter. One cow did dry herself off, and there is one more to cull, but we expected the system wouldn’t suit all.”
They noticed their farm manager, Matias Campello, seemed significantly less stressed during calving. They had a compact 6-week mating period and used sexed semen, so most of the heifer replacements were in the calf shed in the first three weeks.
Ben said they had a similar proportion of cows with health and metabolic issues through calving, but since only half of the herd had calved, the total number was less.
And they noted the reduction in bobby calves.
“We used some beef semen as well, so the only real bobbies were from the two-year-old first-calving cows.”
Emma is keen to continue the trial and looks forward to seeing how calving progresses. She sees the advantages of having a smaller number of cows to mate and calve, but recognises it requires a huge mindset change, particularly seeing the cycling of cows whose mating has been delayed a year.
Follow the project’s progress at dairynz.co.nz/frontier-farms
This article was originally published in Inside Dairy November-January 2026.
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