Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m x 6 in) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 x 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral-detergent fibre, acid-detergent lignin, crude protein and water-soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n-alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseuclostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water-soluble carbohydrate concentration showing large variation (> 0(.)35). Cultivats differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (> 2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High-yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.