Development of a system to rank perennial ryegrass cultivars according to their economic value to dairy farm businesses in south-eastern Australia

Dairy production systems in south-eastern Australia are based primarily on grazed pasture. Perennial ryegrass (Lolium perenne L.) is the major grass species used in this region and farmers are faced with the challenge of choosing from more than 60 commercially available cultivars. This paper describes the development of a system termed as a forage value index that ranks the overall performance of perennial ryegrass cultivars relative to cultivar Victorian according to the summation of the estimated difference in the value of seasonal dry-matter (DM) yield of the cultivars. Average predicted seasonal DM yields were calculated by analysing the results of eight available perennial ryegrass plot trials across south-eastern Australia, using a multi-environment, multi-harvest linear mixed model. The differences in the model-predicted DM yield of each cultivar was compared with cultivar Victorian in each of five seasonal periods (autumn, winter, early spring, late spring, summer) to generate a series of performance values (1 per period) for each cultivar. Each performance value was then multiplied by an economic value (AU$/kg extra pasture grown) relating to each of four regions (Gippsland, northern Victoria, south-western Victoria, Tasmania) and seasonal period and aggregated to generate an overall forage value index rating for each cultivar. Economic values ranged from AU$0.11 to AU$0.39 per extra kilogram of DM grown, depending on the season and region, which translated into estimated benefits on dairy farms of up to AU$183 per ha per year for farmers that use high-yielding cultivars in place of cultivar Victorian perennial ryegrass.