However, Fonterra was planning to introduce a demerit grading system, with financial penalties for farmers supplying milk that exceeded acceptable Fat Evaluation Index (FEI) limits, which would limit the use of PKE. Those who had previously used high levels of PKE would need to consider and understand options to keep milk FEI below acceptable limits.
In some cases, the FEI would show the need to reduce the use of PKE.
"This is going to result in them having to change their systems. We hope they can learn from what we have been studying at NARF," Mr Boom said.
NARF was split into three small farms. One used only home-grown pasture, the second grew supplementary crops and the third farm used PKE to fill feed gaps.
Last season the PKE farm had the highest production, at 1118kg MS/ha, followed by the cropping farm (1053kg MS/ha) and the grass-only farm (965kg MS/ha).
In the 2015/16 season the grass-only farm was slightly more profitable than the others at the milk price of $3.90/kg MS, despite having the lowest production. With a milk price of $6.12/kg for the 2016/17 season, farm profit was very close between the grass-only and PKE farms, while the cropping farm was lower.
This year's wet winter and spring conditions had challenged the grass-only and cropping farms, while the PKE farm had "sailed through" without too much problem.
"Very soft soils that had been cropped the previous season are a struggle during a wet winter/spring like we just had," Mr Boom said.
Details of the results and how the non-PKE farms were run will be presented at Thursday's field day, with Dr John Roche ('Are you making money from milk or milk from money?') having done a significant amount of trial analysis along with other datasets, offering recommendations for when supplement use is profitable and how to get the most out of it.
Presentations at the Okaihau Hall will be followed by a visit to Roger and Jane Hutchings' farm, where the hosts will talk about reducing PKE, and Tim Johnstone will explain Fonterra's FEI testing and what is known about the effect of different feeds on milk FEI.
"Use of PKE is going to be challenged," Mr Boom said.
"When the penalties come in then all Fonterra suppliers will need to know about the interaction of PKE and FEI on their farms.
"The sooner this learning is done the better Fonterra suppliers will be able to plan for alternative supplements. This is something we don't need to worry about on the grass-only farm, but as we will show, grass-only farming is not always easy.
"The NARF trial demonstrates what we see as best practice in how each of these systems operate," he added.
"Not that we get it right all the time. Getting the grass-only farm through this wet winter/spring was challenging.
"It is great that we have these climatic challenges in trials like this. It is easy to farm when the sun and rain come in the right ratios, but most of life is not like that."
The field day starts 10am at the Okaihau Hall, all welcome, no cost, no RSVP required, barbecue lunch provided.
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