Both companies were sentenced under the Health and Safety at Work Act 2015 and were fined $247,500, with each company to pay half the amount.
Reparation of $110,000 was also ordered to be paid to the victim's family and apportioned equally between both businesses.
A WorkSafe investigation found that the condition of the quad bike was consistent with an ATV that had been in regular use but had not been serviced for a prolonged period. The quad bike's brakes, steering, suspension and front bull bar/bumper were all in need of servicing or repair.
The investigation concluded that the quad bike was not fit for use in a farming environment.
WorkSafe area investigation manager Steve Kelly said: "There are far too many preventable quad bike accidents happening across New Zealand. This is another tragic reminder that farm vehicles such as quad bikes must be regularly serviced and adequately maintained."
On average, five people die in work-related quad bike accidents each year and many more are injured. Most quad bike injuries and fatalities are caused by the quad bike rolling over.
WorkSafe's recommendation was that businesses consider installing crush protection devices (CPDs) on the back of quad bikes.
ACC offers a cash-back offer on CPDs, and WorkSafe urges operators to take advantage of the offer.
"A CPD is a simple and valuable way of keeping users safe," Kelly said.
"While the companies had purchased a CPD for the quad bike involved, this was not installed at the time of the accident. However, the poor maintenance and servicing of the machine would still have exposed users to significant risk.
"Dairy Holdings needed to have developed, implemented, monitored and reviewed an effective safe system of work for employees operating the quad bike at Coryston Farm. Coryston should have ensured the quad bike was properly serviced and maintained."
