Technical Abstract: Increased production from less productive lands limited by irrigation can be increased if genetically improved pasture grasses are developed with increased tolerance to abiotic and biotic stresses. In 2000, 18 half-sib families of meadow bromegrass were seeded in a split plot design under a line-source irrigation design to estimate genetic variability and parameters as affected by irrigation level and harvest date on dry matter yield (DMY), crude protein (CP), in vitro true digestibility (IVTD), neutral detergent fiber (NDF), and digestible neutral detergent fiber (dNDF). At all water levels (WLs) genetic variation for total DMY among half-sib families was not different than zero; however, at WL-5 narrow-sense heritability (h2) estimate increased to 0.48 plus or minus 0.36 as water stress increased. Genetic variation for CP in this population was limited and was influenced more by harvest date than WL. Heritability estimates for IVTD were significant regardless of WL and harvest date. There was a trend toward increased h2 estimates in IVTD concentrations from early-to late-season harvested forage. There were no trends in NDF across WLs, but h2 estimates were highest in forage harvested later in the growing season. Heritability estimates for dNDF were small or associated with large standard errors. Based on correlations at WLs 1 and 3, it seems reasonable to assume that when selecting in this population for increased DMY that NDF will increase and that IVTD, dNDF, and CP concentrations will decrease. Under the highest water stress, DMY was positively correlated to CP, IVTD, and dNDF and negatively correlated to NDF, possibly resulting from a higher leaf to stem ratio at WL5.