Genetics and good feeding ensured continual improvement in the nation's cows' milking productivity, LIC New Zealand markets general manager Malcolm Ellis said.
In the South Island, milk production rose 2% in 2015-16. Marlborough-Canterbury's increase was 2.5% and Otago-Southland's 2%, while West Coast-Tasman fell 0.8%.
"The South Island now produces 42.7% of national milk solids production, compared with only 31.1% a decade ago," Mr Ellis said.
North Island production fell 3.9% in 2015-16, with all regions except Northland (which had no change) producing less milk than in 2014-15.
Overall herd numbers fell for the first time since 2007-08, now totalling 11,918. North Island herd numbers declined 122 to 8696, while South Island herds increased 70 herds to 3222.
Farm ownership structures also changed - 30.0% of New Zealand dairy herds operated under a sharemilking agreement in 2015-16, compared with 32.4% the previous season.
Within the sharemilker herds, 20-29% sharemilkers decreased by 229 herds (-22%) to 821 and 50:50 sharemilkers declined by 57 herds (-2%) to 2422. Owner-operator herds increased 256 to 8315 herds in 2015-16, reflecting variable order sharemilkers moving to contract milking agreements after financial challenges with low milk prices in recent seasons.
"The number of cows milked in 2015-16 declined 0.4% to just under 5 million, despite a very high number of culled cows during the last two seasons," Mr Newman said.
"This reflects a high number of replacement heifers entering the milking herd in 2015-16, plus some carryover cows being culled. A further decline in the number of cows milked is expected this season."
Holstein-Friesian/Jersey crossbreeds now account for 47.2% of cows - up from 45.6% in 2014-15. Holstein-Friesians make up 33.5% of the national herd, compared to 34.7% in 2014-15, and Jerseys comprise 10.1% compared to 10.4% the previous season.
Artificial insemination was used on 71.1% of cows in 2015-16, a 3% drop on 2014-15. The number of yearling heifers mated through AI also declined by 26% - the lowest number since 2010-11.
"However, farmers understand the value of herd improvement and the expectation is for activity to rebound in line with the milk price," Mr Ellis said.
The average six-week in-calf rate eased from 66.8% in 2014-15 to 66.5%. In the past five seasons the national six-week in-calf rate has remained relatively steady at around 67%.
Herd testing was at the lowest level on record at 61.4%, down from 72.9% as farmers cut costs.