Genetic variability for stem cell wall (CW) digestibility could be exploited to improve rumen‐fermentable energy in alfalfa (Medicago sativa L.) forage. We evaluated in the field the response to recurrent selection for stem CW digestibility in alfalfa. Digestibility was assessed as the concentration of glucose released after enzymatic hydrolysis of fiber (enzyme‐released glucose, ERG). Two initial cultivars, 54V54 and Orca, and populations obtained after successive cycles of divergent selection for stem CW digestibility (D−1, D−2, D+1, and D+2) were established at three field sites in north, central, and south of Québec. Field trials conducted over two growing seasons showed that populations obtained after two selection cycles (D+2) had significantly higher CW digestibility (+20.7 mg ERG g⁻¹ CW) than initial cultivars (average of 13% improvement of digestibility). The D+2 populations did not differ from the initial cultivars with regard to biomass yield, winter survival, and stem water soluble‐carbohydrate concentration. Increases of ERG concentrations were observed in response to each selection cycle, and broad‐sense heritability highlights a moderate control of genetic factors over environmental factors for CW digestibility. Recurrent selection for stem CW digestibility is a valuable approach to increase fermentable energy in alfalfa forage and improve N utilization by ruminants.