Perennial Ryegrass Variety Differences in Nutritive Value Characteristics

Animal grazing performance at grass is predominately determined by herbage intake rates, with high yielding dairy cows requiring up to 20 kg/d DM within a limited grazing time (Gibb, 1998). Grass nutritional factors such as seasonal patterns in digestibility and water-soluble carbohydrate levels have been linked to animal productivity (Davies et al., 1991), while sward surface height, herbage mass, bulk density and green leaf mass have been shown to promote high grazing intake (Barrett et al., 2001). Furthermore, fatty acid profiles have been shown to improve the unsaturated fatty acid composition of milk, with potential human health benefits (Parodi, 1997). Recent CAP funding changes are expected to intensify the drive to optimise margin over costs. Given that grazed grass is the cheapest ruminant feed, it is expected that nutritive value characteristics of grass varieties will become increasingly important relative to total productivity, both as a breeding objective and as an evaluation criteria by variety testers and by farmers. This study examined the genetic diversity in such parameters among a wide range of perennial ryegrass (Lolium perenne L.) varieties, as an indicator of the heterogeneity among current varieties and the prospects for improvement by selective breeding