Global population increases have expanded livestock industries and the demand for forage production. These factors have necessitated forage production with poor-quality irrigation water in semi-arid and arid regions. A greenhouse study evaluated the effect of poor-quality irrigation water on seedling growth to 90 days after planting alfalfa (Medicago sativa) and triticale [×Triticosecale Wittm. ex A. Camus (Secale × Triticum)], which were selected as representative forage crop species. Treatments were: fresh water (control; 0.7 dS m-1), brackish groundwater (BGW; 4 dS m-1), reverse osmosis concentrate (ROC; 8 dS m-1; Ca dominant), and BGW plus sodium chloride (BGW+NaCl; 8 dS m-1; Na dominant). Treatment influences on germination have been reported. This article reports the potential influence of those treatments during that 90-d period after which newly spring-seeded alfalfa would normally be harvested the first time and triticale would typically be ready to graze. Increasing salinity of the irrigation water had no effect on forage crude protein content, but it reduced acid detergent fiber and amylase-treated neutral detergent fiber (aNDF) (375, 310, 300, 319 g kg-1 aNDF for the control, BGW, ROC, and BGW+NaCl treatments, respectively; P < 0.05, SED = 15) and increased non-fiber carbohydrates. Further research at the field level and over a longer period for alfalfa is needed to validate the results of this preliminary study and to evaluate the influence of poor-quality water for irrigating these and other forage crop species.