This dataset contains grassland yield, forage content, and nutritive quality data from a three-year plot trial (2019–2021) at Teagasc Athenry, Co. Galway. The trial examined four sward types (perennial ryegrass mixtures with white clover, red clover, plantain, and chicory) under four different establishment methods. Measurements included herbage yield, sward composition, tiller density, and forage quality parameters (crude protein, dry matter digestibility, water soluble carbohydrates). Data were collected by Lisa McGrane and Philip Creighton, with sward quality analysis using Near Infrared Spectrometry (NIR) at Teagasc Moorepark.