Development and application of an economic ranking index for perennial ryegrass cultivars.

Economic values in euros (€) were calculated for traits of economic importance in Irish grass-based systems. The economically important traits selected were spring, midseason, and autumn grass dry matter (DM) yield (€/kg of DM per ha), grass quality (€ per unit DM digestibility), first- and second-cut silage DM yield (€/kg per ha), and sward persistency (€/% change in persistency per ha per yr). The economic value for each trait was calculated by changing the trait of interest while keeping all other traits constant, using the Moorepark Dairy Systems Model. Herd parameters (including cow numbers and calving pattern), milk production, energy demand, supplementary feeds, and land area were readjusted to calculate the economic value for the trait of interest. The base scenario assumed fixed cow numbers with 40 ha of land available, with full costs included. The results for the base scenario show the economic values were: €0.15/kg of DM spring yield, €0.03/kg of midseason yield, €0.10/kg of DM autumn yield, the quality value was €0.001, €0.008, €0.010, €0.009, €0.008, and €0.006 per unit change in DM digestibility/kg of DM yield for the months of April, May, June, July, August, and September, respectively; €0.036/kg of DM first-cut silage; €0.024/kg of DM second-cut silage; and -€4.961 per 1% decrease in persistency/ha per yr. Sensitivity of the economic values to changes in milk price and scenario were tested. The economic values were applied to experimental production data collected over 3 yr for 20 perennial ryegrass cultivars to establish the total economic merit for each cultivar and then to rank each cultivar based on its economic performance. Rank correlations between the base and alternative scenarios ranged from 0.90 to unity. This indicates that the economic values are reliable regardless of system, intensity, or price. The total merit index will identify the cultivars that can make the greatest economic contribution to a grass-based production system.