Forage Value Index

We have completed a four-year trial at Scott Farm in the Waikato, validating the Forage Value Index (FVI) under typical farm management conditions.

What is the Forage Value Index?

The objective of the New Zealand Forage Value Index is to identify forages that maximise dairy farm profit. The FVI allows farmers to compare profit rankings (5-star ranking) for different perennial and short-term ryegrass species and cultivars.

Sitting behind these components are two key assumptions:

• That cultivar performance values, derived from small-plot evaluation trials, adequately capture performance under realistic dairy farm management conditions.
• The economic values for pasture performance traits, modelled by the Farmax farm system software, represent the true value of those traits to dairy farm businesses.

The aim of the Forage Value Index Validation trial was to determine if predicted differences in forage value were reflected in pasture grown, milk production and profit (all measured on a per-hectare basis) when cultivars with different FVI rankings were compared in self-contained production systems.

Trial results

We expected that the high-FVI pastures would have a greater total pasture dry matter yield and better seasonality of growth, namely greater growth rates in winter/early spring and autumn relative to the low-FVI pastures.

It was predicted that the advantage to the high-FVI farmlets would be driven by:

• greater total annual DM production (+600kg DM/ha)
• greater whole season milksolids production (+39kg MS/ha), from
  • more days in milk (+7 days)
  • greater daily production
• lower production costs, from
  • less purchased supplements (-500kg DM/ha)
  • less home-grown silage harvested (-600kg DM/ha)

Data from previous DairyNZ small plot trials was modelled using Farmax to develop the predicted outcomes.

The FVIV trial had the statistical capability to detect a $300-400/ha difference (with 90% certainty), thus we were 90% sure we could expect to detect a $300-400 advantage from the high-FVI treatment; however, this difference did not occur.

So, let’s look at what happened…

Climate

In all four years, the growth rates in January-March were low due to warmer and drier-than-average summers and autumns. The maximum daily temperatures exceeded 25oC for 73 days each year, compared with 28 days per year for the preceding 30-year period.

Below shows the total monthly rainfall from June 2018 to March 2022. The grey bars represent the 30-year means, while the black lines represent data during the experiment.

There was a change in pasture cover on DairyNZ's Scott Farm, Hamilton, between December and January in each of the four years of the trial. Red is no pasture, yellow is low pasture, and green is abundant pasture. Paddocks enrolled in the Forage Value Index Validation trial were distributed across the farm. Satellite images from LIC SPACETM

Milk production

Our prediction of more days in milk for cows in the high-FVI farmlets assumed there’d be more pasture available in autumn on those farmlets. However, dry conditions in all four years of the trial meant cows were dried off at similar times in both the high- and low-FVI farmlets.

• In the first three seasons during peak lactation, milksolids production for cows grazing both high- and low-FVI cultivars was less than predicted.
• Over the four seasons, there was no significant difference in whole season milksolids production between high- and low-FVI cultivar farmlets.

Feed supply and demand

We predicted there’d be better alignment between pasture supply and demand in farmlets using high-FVI cultivars, resulting in less demand for purchased supplementary feed (-500kg DM/ha) and less need to harvest silage (-600kg DM/ha).

The graph below shows the difference between high and low cultivars for purchased supplements, silage made on-farm, and pasture renovation over four years. Note: the label on the high-FVI bar is the difference between the high- and low-FVI farmlets.

Silage made on-farm

The differences in silage harvested between farmlets with high- or low-FVI cultivars were less than predicted, and in 2020/21, more silage was harvested from high-FVI farmlets. This was because greater pasture renovation in farmlets with high-FVI cultivars in autumn 2020 resulted in nitrate toxicity levels preventing spring grazing.

Pasture renovation

Throughout the four-year trial, 71% of the high-FVI and 49% of the low-FVI area required pasture renovation (undersowing).

Economics

Profit from productivity is a measure designed by DairyNZ to describe dairy farm profit per hectare arising from productivity improvements, rather than from other factors such as changes in payout or input prices. Our expectation of a greater profit from productivity (milk revenue minus purchased supplements, silage made on-farm, and pasture renovation expenses) of around $300-400/ha from high-FVI cultivars did not occur.

• During the first three seasons, milk production and revenue were similar for all farmlets.
• However, the high-FVI farmlets incurred more costs than predicted for purchased supplementary feed, silage harvesting and pasture renovation.
• Only in the last season (2021/22), with milksolids production similar and expenses less, did the high-FVI farmlets return a positive margin (+$73/ha). This was still lower than predicted.
• The positive marginal return from the high-FVI farmlets in 2021/22 indicates that the change in tactical management suited the performance of these cultivars.

The table below shows the profit from productivity advantage ($/ha) to high-FVI treatment compared with low-FVI treatment.

What next?

DairyNZ will continue investigating this research and use this data to improve the FVI to ensure it is a practical and robust resource for farmers. The findings will be shared with farmers as they are available, and feed into the ongoing improvements to the FVI.

More detail on the FVI trial design

Testing assumptions underlying the FVI under common farm management conditions is essential in ensuring the FVI delivers the best possible results.

Forty hectares (ha) of pasture on DairyNZ's Scott Farm, just outside Hamilton, was progressively sown over two years from 2016-2018, half in high-FVI and half in low-FVI perennial ryegrass cultivars (diploid, common endophyte). The trial ran for 4 years, from June 2018 to June 2022.

The high-FVI cultivars were selected from the four- and five-star rating bands for the Upper North Island. The low FVI cultivars were selected from the one- and two-star rating bands.

For each treatment, there were five replicated self-contained farmlets with the following protocols:

• Individual cultivars were sown with white clover and contained AR37 endophyte. The two high and low cultivars were sown in different paddocks, not as a mix.
• Stocked at 3.5 cows/ha.
• Approximately 180 kg/ha of nitrogen (N) fertiliser was applied annually.
• Imported feed was offered only when there was a pasture deficit and to maintain target post-grazing residuals.

The trial was managed under the same conditions for the first three years. Several management changes were implemented in the fourth year, including calving one week earlier and differential winter rotation lengths between high- and low-FVI treatments.

We measured pasture and animal performance indicators including:

• Seasonal pasture dry matter yield of high- and low-FVI pastures, and pasture composition and feed quality throughout the year.
• Milk production grazing high- and low-FVI pastures, and cow body condition score.