Forage Value Index
5 min read
The Forage Value Index (FVI) was designed to help dairy farmers in New Zealand identify superior forages for their farm system by ranking different ryegrass species and cultivars. A four-year trial at Scott Farm evaluated the FVI under real-world farming conditions. The expectation was that high-FVI pastures would produce more dry matter, leading to increased milk production and profit, and lower production costs.
We have completed a four-year trial at Scott Farm in the Waikato, validating the Forage Value Index (FVI) under typical farm management conditions.
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.
The high-FVI cultivars were selected from the four- and five-star rating bands and the low-FVI cultivars were selected from the one- and two-star rating bands.
The two key components required to calculate the FVI of a cultivar are:
Sitting behind these components are two key assumptions:
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.
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:
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…
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
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.
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.
For the first three seasons, more supplementary feed was purchased in high- than low-FVI farmlets. In 2021/22, less supplementary feed was purchased in high-FVI farmlets, potentially because pasture management targets were altered in the last season.
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.
Throughout the four-year trial, 71% of the high-FVI and 49% of the low-FVI area required pasture renovation (undersowing).
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 $300-400/ha from high-FVI cultivars did not occur.
The table below shows the profit from productivity advantage ($/ha) to high-FVI treatment compared with low-FVI treatment.
|Year||Advantage to high-FVI treatment|
Standard Error of the Difference (SED) for each year: 2018-19: 107; 2019-20: 269; 2020-21: 202; 2021-22: 145. No significant difference was detected between means in any year.
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.
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:
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: