This dataset contains grassland yield, forage content, nutritive quality, and tiller density results from a four-year plot trial (2019–2022) conducted at Teagasc Athenry, Co. Galway. The trial tested five different sward types under three post-grazing sward height treatments. 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 carried out using Near Infrared Spectrometry at Teagasc Moorepark.