<span name="style_bold">Agronomic and nutritional evaluation of perennial tetraploid ryegrass-based pastures (<span name="style_italic">Lolium perenne</span>) in dairy farms in the highlands of Costa Rica. I. Dry matter yield and phenology.</span> Dry matter yield and phenology of perennial tetraploid ryegrass (<span name="style_italic">Lolium perenne</span>) in dairy farms in the highlands of Costa Rica. I. Dry matter yield and phenology.<span name="style_italic">Lolium perenne</span>)-based-pastures were evaluated in 4 commercial dairy farms in the district of Chicuá, Oreamuno, Cartago (latitude 09°59’, longitude 83°52’, 3090 m of altitude) every two months during a one-year period. Average pre and postgrazing dry matter availability, utilization per hectare and percentage of utilization were 4110, 2276 and 1833 kg.ha<span name="style_sup">-1</span> per grazing cycle and 44.82%, respectively. Average phenological stage and leaf:stem ratio were 2.84 green leaves per regrowth and 56:44. Botanical composition of ryegrass-based-pastures was 76.09% ryegrass, 13.76% other grazes (mainly kikuyu grass), 6.02% clover, 1.25% weeds and 2.88% senescent material, respectively. These pastures yield a surplus of DM during March and April, which can be conserved to be fed during the months of less pasture availability. Agronomic data show that the grazing system based on the leaf stage concept is a good tool for managing ryegrassbased-pastures in the highlands of Costa Rica. per grazing cycle and 44.82%, respectively. Average phenological stage and leaf:stem ratio were 2.84 green leaves per regrowth and 56:44. Botanical composition of ryegrass-based-pastures was 76.09% ryegrass, 13.76% other grazes (mainly kikuyu grass), 6.02% clover, 1.25% weeds and 2.88% senescent material, respectively. These pastures yield a surplus of DM during March and April, which can be conserved to be fed during the months of less pasture availability. Agronomic data show that the grazing system based on the leaf stage concept is a good tool for managing ryegrassbased-pastures in the highlands of Costa Rica.

Dry matter yield; phenological stage; utilization; temperate climate grasses; Lolium perenne