Cultivar effects of perennial ryegrass on herbage intake by grazing dairy cows

Perennial ryegrass is the most abundant grass species in temperate climates. An increased herbage intake of dairy cows by breeding new cultivars could have a large potential impact on agriculture. The effects of cultivars on sward structure, nutritive value, physical characteristics and disease resistance of perennial ryegrass are discussed. Cultivar differences were found in several studies for plant factors such as dry-matter yield, green-leaf mass and bulk density. Clear cultivar differences in nutritive value of perennial ryegrass were observed, especially the cultivar rankings for concentrations of water-soluble carbohydrates and acid detergent lignin were found to be consistent during the season and across years. Cultivar effects were also found for physical characteristics, e.g., tensile strength and resistance against crown rust (Puccinia coronata f. sp. lolii). The different plant-related cultivar effects were evaluated for their effects on herbage intake by grazing dairy cows. Differences among cultivars for the concentration of water-soluble carbohydrates affected the preference behaviour of dairy cattle. The possibilities to enhance dry-matter intake in a grazing situation through breeding can mainly be achieved by selecting for a better crown-rust resistance and a higher dry-matter production. A higher dry-matter production would give more opportunities for selection by dairy cows and might, therefore, enhance herbage intake at the animal level, but the production of more herbage would certainly enhance herbage intake at farm level.