The Forage Value Index’s (FVI) ongoing development has been supported by a comprehensive programme of levy-funded research. DairyNZ is now moving the tool into a validation phase, where we’ll test if the FVI systems work under realistic farm management conditions.
Why are we doing this?
The FVI ranks ryegrass cultivars on their expected economic value to New Zealand dairy farm businesses. To calculate the FVI of a cultivar, two key components are required: the cultivar’s performance value for individual traits, and the economic value of those traits to dairy farm businesses.
Sitting behind these components are two key assumptions:
- That the economic values calculated for pasture performance traits, from the Farmax farm system model, are representative of the true value of those traits to dairy farm businesses.
- That cultivar performance values, derived from small-plot evaluation trials, adequately capture performance under realistic dairy farm management conditions.
If these assumptions hold under realistic farm management conditions, we have good evidence that the FVI is a robust decision support tool. Essentially, we want to know that the FVI ‘does what it says on the tin’.
How are we doing this?
To test the FVI systems, we’ve taken selected cultivars from the FVI into a farm systems experiment to determine if dry matter (DM) yield performance differences emerge as expected. We can then compare the relative profitability rankings of the cultivars from the experiment with their relative profitability rankings in the FVI. This is akin to the dairy cow strain trials undertaken in the early 2000s to validate and develop animal evaluation indices.
On DairyNZ’s Scott Farm, just outside Hamilton, 40 hectares (ha) of pasture were sown to high- and low-ranked FVI cultivars over the past three autumns (to 2018). The high-ranked FVI cultivars were selected from the five-star rating band in the FVI for the Upper North Island. The low-ranked FVI cultivars were selected from the one- and two-star rating bands. All cultivars were sown with white clover, as is standard farm practice. Low-ranked FVI cultivars were sown on one 20-ha pasture area and high-ranked FVI cultivars were sown on the other, for comparison over three years from June 1, 2018.
Both areas are stocked at 3.5 cows/ha, and will receive 180 kilograms (kg) of nitrogen (N) fertiliser annually. Imported feed will be offered only when there’s a true pasture deficit to maintain target post-grazing residuals.
Where is the value?
We expect the high-FVI pastures will have a greater total pasture DM yield and better seasonality of growth, i.e. greater growth rates in winter/early spring and autumn relative to the low-FVI pastures (see Figure 1). Modelling results indicate that the more favourable pasture growth curve of the high-FVI pastures will generate $300 to $400 of additional operating profit per hectare per year compared with the low-FVI pastures, through a lower requirement for imported feed and, to a lesser extent, more days in milk in autumn.
Data from small-plot evaluation trials also indicate that the high-FVI pastures will maintain better pasture quality in late spring and early summer, which is potentially worth $50/ha per year.
Cultivar performance (and consequently, system performance) expectations have been derived from carefully managed small plot evaluation trials. An important objective of this experiment is
to determine if expected differences in cultivar performance from small-plot evaluation trials holds true when cultivars are sown at a paddock scale and managed under realistic farm management conditions.
What will we measure?
Several pasture and animal performance indicators will be measured as part of the experiment. We will measure the seasonal dry matter yield of the high- and low-FVI pastures, and pasture composition and feed quality throughout the year. The milk production of cows grazing the high- and low-FVI pastures will measured, and cow body condition score will be routinely assessed.
To determine if the profit rankings of the high- and low FVI pastures correspond with their relative position in the FVI, we’ll calculate the operating profit (on a per-hectare basis) of each system, using results for production and the amount of inputs required to maintain target pasture covers and cow body condition scores.