Forage Value Index

Most recent FVI update

DairyNZ and the Plant Breeding Research Association (PBRA) are committed to working together to understand the root causes of the FVI validation trial result. Until the predicted economic differences among cultivars listed in the FVI can be demonstrated, FVI economic rankings will not be published.

DairyNZ removed the Cultivar Selector Tool on the 19th of March 2024.

• DairyNZ ran a four-year farm systems trial at Scott Farm in the Waikato, looking to validate the FVI through differences in dry matter (DM) yield, milk production, and farm profitability between higher and lower FVI diploid ryegrass cultivars with the same AR37 endophyte. The DairyNZ FVI modelling projected a $300-$400/ha difference between treatments.
• The results of the validation trial showed that the predicted milksolids production and operating profit expected from ryegrass dry matter yield measured at the plot scale was not able to be captured in this single farmlet scale trial.
• Until the predicted economic differences among cultivars listed in the FVI can be demonstrated, the FVI economic rankings will not be published. Measured yield differences from NFVT plot trials will continue to be supplied to farmers (see pbra.co.nz/trial-data/forage-grasses).
• Selecting the right cultivar for each farm is important. DairyNZ acknowledges that plant breeding is a complex process and has provided NZ farmers with a range of high-performing cultivars. Substantial progress has been made with novel endophytes, ploidy options, yields and changing of heading date. Farmers can have confidence in these advances and should continue to ensure they select high-yielding cultivars with the endophyte, ploidy and heading date that suits their farm system.

Further information is provided to support your decisions on the cultivar selection page.

The background

In 2012, the Forage Value Index (FVI) was launched in partnership with the Plant Breeding and Research Association (PBRA). The FVI categorises perennial and short-term ryegrass cultivars into five star ranking groups across the four dairy regions: upper and lower North Island, and upper and lower South Island. Those with a higher star rating were predicted to deliver greater economic benefits for dairy farmers.

Key components

The two key components required to calculate the FVI of a cultivar are:

• The cultivar's performance value for individual traits.
• The economic value of those traits to dairy farm businesses.

Sitting behind these components are two key assumptions:

• That cultivar performance values, derived from the National Forage Variety Trials (NFVTs) run by PBRA, 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.

Since 2012, other traits, such as metabolisable energy (ME), and persistence, have been included.

The predicted benefit from higher FVI cultivars

Before the validation experiment began, data from previous DairyNZ small plot trials was modelled using Farmax to develop the predicted outcomes. The Forage Value Index validation trial was designed to detect a $300-400/ha difference between treatments, as the DairyNZ FVI modelling predicted.

The predicted difference in profit would be from greater daily production and lower production costs, explained by:

Dry matter yield

• Higher FVI cultivars would have a greater total annual dry matter production (+600kg DM/ha).
• Different seasonal growth, i.e., greater growth rates in winter and early spring and autumn, and lower growth rates in late spring, compared with lower FVI cultivars.

Supplementary feeds

• A better match between pasture demand and supply would reduce the need for imported supplementary feed (-500kg DM/ha) during winter/early spring and autumn.
• Reduce the need to make and feed silage (-600kg DM/ha).

Milk production

• Greater pasture supply in early spring and autumn would result in greater milk production in the higher FVI treatment (+39 kg MS/ha per year).
• More days in milk (+7 days).

Trial Design

In 2015, a farmlet-system comparison trial was designed to validate the FVI rankings under realistic farm management conditions on DairyNZ’s Scott farm in the Waikato.

Sowing of pastures began in 2016, with five farmlets containing higher FVI (4- and 5-star) cultivars, and five farmlets with lower FVI (1- and 2-star) cultivars chosen from the 2015 FVI lists. All cultivars were diploid perennial ryegrasses and were sown individually with white clover.

Endophyte

The endophyte AR37 was chosen due to the location of the trial in the Upper North Island, meaning an endophyte that provided greater protection against damage from insects such as Black Beetle was required. The choice of a single endophyte meant that the low-yielding cultivars with other endophytes were not considered. Designing the trial this way meant that we could test the yield benefits of higher FVI cultivars without any confounding effects of endophyte or ploidy.

Trial management

The trial was managed under the same conditions for the first three years, stocking rate, herd replacement rate and planned start of calving were kept the same for the higher and lower FVI treatments. Several management changes were implemented in the fourth year, including calving one week earlier and different winter rotation lengths between higher and lower FVI treatments.

Data collection and measurements

Between 2018 and 2022, data on farmlet performance (animals, pasture and feed) was collected to determine the physical and financial benefits of the higher and lower FVI cultivars. Poor-performing pastures in both treatments were renovated (full or partial) as required to maintain the plant population.

Pasture measurements included dry matter yields, pasture composition and feed quality. Milk production of cows was measured, as well as cow body condition score. Feed measurements included silage harvested and imported supplementary feed.

Industry collaboration

To ensure the trial was robust, representatives from the PBRA along with national and international science experts were involved in the planning and implementation phases. Four Waikato dairy farmers regularly engaged with the project to ensure tactical and strategic management decisions (e.g., shortening winter round lengths) aligned with best practices on-farm.

What was discovered

Profit

During the first three seasons, milk production and revenue were similar for all farmlets. However, the higher FVI farmlets incurred more costs than predicted for purchased supplementary feed, silage harvesting and pasture renovation.

Only in the last season (2021/22), with similar milksolids production and less expenses, did the higher FVI farmlets return a positive margin (+$73/ha). This was still lower than predicted. The positive marginal return from the higher FVI farmlets in 2021/22 indicates that the change in management may have suited the performance of these cultivars.

The relative differences in profit (calculated from milk revenue less costs associated with supplementary feed and silage making, and pasture renovation), for farmlets with higher FVI pastures compared with lower FVI pastures are presented below. No significant difference was detected between treatments in any year.

Feed supply and demand

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

Purchased supplements

For the first three seasons, more supplementary feed was purchased in higher than lower FVI farmlets. In 2021/22, less supplementary feed was purchased in higher FVI farmlets, potentially because pasture management targets were changed in the last season.

Silage made on-farm

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

Pasture renovation

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

The graph shows the difference between higher and lower cultivars for purchased supplements, silage made on-farm, and pasture renovation over four years.

Milk production

Our prediction of more days in milk for cows in the higher 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 higher and lower FVI farmlets.

In the first three seasons during peak lactation, milksolids production for cows grazing both higher and lower FVI cultivars was less than predicted.

Over the four seasons, there was no significant difference in whole-season milksolids production between higher and lower FVI cultivar farmlets.

The review

To understand why the relative difference in profit differed from predictions, an in-depth review of farmlet performance was undertaken by DairyNZ and several areas were explored. Some of these results from this investigation are covered here.

Summer-autumn dry

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. Rainfall in January and February was approximately 50% of the 30-year average.

This reduced the opportunity for the late-heading, higher FVI cultivars, bred for superior summer-autumn growth, to achieve their potential. With a pasture deficit for all farmlets in autumn each year, cows in all farmlets were dried off at a similar time. Thus, the predicted extra milksolids production from more days in milk and the subsequent milk revenue for the higher FVI farmlets did not occur.

To determine if the dry autumn weather was the primary cause of the less-than-predicted profit, we re-ran the FVI model, reducing the value of autumn pasture to reflect the dry conditions. The predicted profit difference between treatments was only reduced by 25%. This indicated that the dry autumn conditions and lack of autumn pasture growth were important factors but did not fully account for the less-than-predicted profit difference in the higher FVI treatment.

Pasture growth

While autumns were dry, conditions for ryegrass growth were good in winter and early spring. These were seasons when the yield advantage was expected to favour the higher FVI treatment, and this did not happen.

Cultivar choice

Continued improvement in ryegrass over the past eight years means that there are now higher ranked cultivars on the FVI than were available when the FVIV trial was established. The higher FVI cultivars used in the trial are ranked 3-Star in the 2023 FVI. An analysis using the 2023 FVI values indicated the predicted performance gap between the higher and lower FVI cultivars selected in 2015 and used in the trial remained greater than $300-400/ha.

In summary

DairyNZ ran a four-year farm systems trial at Scott Farm in the Waikato, looking to validate the FVI through differences in dry matter (DM) yield, milk production, and farm profitability between higher and lower FVI diploid ryegrass cultivars with the same AR37 endophyte. The DairyNZ FVI modelling projected a $300-$400/ha difference between treatments. The results of the validation trial showed that the predicted milksolids production and operating profit expected from ryegrass dry matter yield measured at the plot scale was not able to be captured in this single farmlet scale trial.

What’s next for the FVI

• DairyNZ and PBRA are committed to working together to understand the root causes of these results.
• Until the predicted economic differences among cultivars listed in the FVI can be demonstrated, the FVI economic rankings will not be published. Measured yield differences from NFVT plot trials will continue to be supplied to farmers (see pbra.co.nz/trial-data/forage-grasses).