Testing the Forage Value Index at scale in the Waikato

Data was collected to determine whether the physical and financial performance of farmlets with higher- or lower-FVI cultivars was as predicted by the FVI. Here’s what was found.

In 2012, the FVI was launched in partnership with the Plant Breeding and Research Association (PBRA). The FVI categorises cultivars into star-rating groups in 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.

A cultivar’s FVI rating is derived from dry matter (DM) yield performance data in replicated plots from the National Forage Variety Trials (NFVTs) run by PBRA, and the modelled (using Farmax) economic value for yield. Since 2012, other traits, such as metabolisable energy (ME), and persistence, have been included.

Validation trial

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. All cultivars were diploids, contained the endophyte AR37 and were sown with white clover.

The endophyte AR37 was chosen due to the Waikato location, and a need to provide greater protection against damage from Black Beetle. This trial design meant we could test the yield benefits of higher-FVI pastures without endophyte or ploidy confounding the trial results.

Between 2018 and 2022, data on farmlet performance (e.g., milk and pasture production, silage harvested, imported supplementary 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.

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.

Predicted benefit from higher-FVI cultivars

Pasture growth data collected between 2012/13 to 2014/15 from a DairyNZ ryegrass cultivar plot trial on Scott Farm (Waikato) was used to model farm performance with higher- and lower-FVI pastures. The model predicted that a farm sown with higher-FVI pastures would generate $300-400/ha per year additional operating profit compared with lower-FVI pastures.

The difference in profit would be explained by:

Dry matter yield – The data predicted that pastures containing higher-FVI cultivars would have a greater total DM yield and 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 (Figure 1a).

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

Milk production– The predicted 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; Figure 1b).

What did we find?

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 in Table 1 below. In no year was there a significant difference in profit between the higher- and lower-FVI cultivars.

To understand why the relative profit differed from predictions, an in-depth review of farmlet performance was undertaken, and several areas were explored. The results from three of these investigations are:

1. Summer-autumn dry

Pasture growth rates between January and March were less than expected in all four years due to warmer and drier-than-average summer-autumns. 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, and 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 lessthan- predicted profit difference in the higher-FVI treatment.

2. Pasture growth and supplementary feed

While autumns were dry, conditions for ryegrass growth were good in winter and early spring, and these were seasons when the yield advantage was expected to favour the higher-FVI treatment.

Measured feed inputs (supplementary feed eaten) and outputs (animal energy requirements, and silage harvested) were used to estimate pasture eaten. Across the four years, the relative difference between the higher and lower farmlets in annual imported supplements, silage offered and pasture eaten was not in the range expected from modelling (Table 2).

3. Cultivar choice

As the FVI has been updated annually since 2015 with new data, there are now higher-ranked cultivars on the FVI than when the trial began. The higher-FVI cultivars used in the trial are ranked 3-Star in the 2023 FVI. We checked that the higher and lower cultivars selected in 2015 still maintain a relative difference in the Upper North Island index today. An analysis with the 2023 FVI values indicated the predicted performance gap between the higher-and lower-FVI cultivars used in the trial remained greater than $300-400/ha.

What’s next for the FVI

• The results of the validation trial showed that the predicted milksolids production and operating profit expected from ryegrass DM yield measured at the plot scale was not able to be captured in this single farmlet scale trial.
• 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).

Acknowledgements

DairyNZ conducted this research under the Forage Value Supporting Science research programme, funded by the DairyNZ Levy.

This article was originally published in Inside Dairy February-March 2024.