Other factors, like palatability, should also be close to inclusion.
The FVI currently gives a basic star rating system to compare cultivars based on drymatter (DM) production but trials are under way to gather more information. The Plant Breeders Association (NZPBRA) is jointly involved in the FVI and is running persistence trials across eight sites this season on commercial farms, five in the northern half of the North Island.
NZPBRA technical forage committee chair Michael Norris said the cultivars in trial plots within paddocks wouldn’t get any special treatment and would be grazed by cows along with the rest of the paddock. The northern sites had been selected because they were expected to have persistence challenges from insect attack or dry conditions. Plant populations would be measured at regular intervals to determine survival and it was likely to be three years before meaningful results would be available. A range of cultivar and endophyte combinations had been sown and would be added to as more cultivars became available.
As well as persistence, nutritive values will be assessed over a two-year period on small plot trials under irrigation in Canterbury starting next year. This hasn’t been done before on an ongoing, independent basis.
DairyNZ principal scientist Dr Dave Chapman said crude protein, metabolisable energy (ME) and neutral detergent fibre (NDF) would be measured, initially on a regular basis through the season, but more work was being done to ensure the other relevant quality parameters were tested. ME was a function of digestibility but additional factors, such as fibre degradability, might also help build a picture of how cultivars differed from one another.
Palatability is also being looked at for inclusion in the FVI, with work being carried out on how to measure and evaluate it. Chapman said pasture quality values gave some hints, as would leaf to stem ratios, but other measures might be needed to give a better overall picture of palatability.
That included how efficiently cows would graze cultivars to a predetermined residual, which was also a measure of intake and DairyNZ was initiating work to look at cow intakes, which could be scaled up to farm-based studies
DairyNZ is also collaborating with Irish researchers to investigate factors that could have an impact on quality, palatability and long-term yield.
Although only a limited number of cultivars have been evaluated and listed on the FVI – based purely on seasonal DM production – more are to be added this month.
The star ranking available now is based on the DM yields as measured by the NZPBRA national forage variety trials (NFVT).
To check the star rankings are right for a commercial situation, eight cultivars of perennial ryegrass are being grown, with or without white clover, with two levels of nitrogen (N) fertiliser applied. They’re being grown at four locations around the country, with the measures focused on DM yield.
Chapman said adjustments would be made to the NFVT information if necessary to give a more robust estimate of relative rankings for total pasture yield, including clover.
He described the FVI as most similar to production worth (PW) in dairy cows, because it used a performance value multiplied by an economic value. The performance value related to the amount of additional DM the NFVT information showed the cultivar grew in either winter, early spring, late spring, summer or autumn relative to a group of base cultivars first tested before 1996.
The economic values put a dollar value on every extra kg of DM and are calculated using a range of assumptions for different regions – upper and lower North and South islands. The model behind the economic values uses regional average farm data for effective area, stocking rate, milksolids (MS) production, lactation length, pasture eaten, forage crops grown, conserved feed, bought-in feed, total feed eaten, ratios of supplements and bought-in feed to feed eaten and N applied.
It then uses financial assumptions for milk price based on a four-year rolling Fonterra historical average, along with costs of various feed inputs, N, the historical two-year cull cow price and regrassing costs.
When a cultivar’s production values are multiplied by economic values for each season they give a dollar value that could be negative or positive depending on how they compare with the 1996 base cultivars and this then determines their star value rating. One star shows the cultivar is in the bottom 20%, with five showing it’s in the top 20% of performers relative to the others listed on the FVI.
The top performers and endophyte combinations are likely to vary depending on the region.
Norris said there had been great buy-in to the FVI from plant breeders, who would be watching the trials closely to make sure the stringent protocols were followed and would give robustness to the data, which was as high as, if not higher than, peer-reviewed scientific papers.
Farmers can see how cultivars compare for their region on the www.dairynzfvi.co.nz website.
