Chemical treatment may improve the nutritional value of corn stalk residues and their potential use as an alternative forage source for lactating dairy cows. The objectives of this study were to determine the effect of prestorage hydration and treatment with 6.6% Ca(OH)₂ on feeding value of corn stalks as an alternative forage source on milk production, milk composition, and DMI. Mid-lactation multiparous Holstein cows (n = 30) were stratified by parity and milk production and randomly assigned to 1 of 3 diets. Corn stalks were chopped, hydrated, and treated with 6.6% Ca(OH)₂ (DM basis) and stored in Ag-bag silos. Treated corn stover was fed in a TMR at 0, 15, and 30% of the diet DM. Treated corn stover replaced either alfalfa haylage (15% stover diet) or replaced alfalfa haylage and an additional portion of corn silage (30% stover diet). Cows were individually fed in tie stalls for 10 weeks. Milk production was not altered by treatment (P = 0.80). Compared with 0% stover diet, DMI was reduced when the 15% stover diet was fed (25.9 vs. 22.7 ± 0.88 kg/d, P < 0.05) and tended to be reduced (25.9 vs. 23.1 ± 0.88 kg/d, P = 0.08) when cows were fed the 30% stover diet. Milk production per unit DMI (kg/kg) tended to increase for cows fed 15% stover diet compared with the 0% stover diet (1.41 vs. 1.62 ± 0.07, P = 0.08) but was not different between cows fed the 0% and 30% stover diets (1.41 vs. 1.50 ± 0.07, P = 0.62). Milk composition, energy corrected milk production, and energy corrected milk produced per unit of DMI (kg/kg) was not different (P > 0.05) among treatments for the 10-week feeding period. Cows fed the 15% and 30% diets had stable DMI and daily milk production over the 10-week treatment period but DMI for cows fed 0% stover increased slightly (time x treatment effect, P < 0.05). These data indicate that corn stover processed through prestorage hydration with Ca(OH)₂ results in an alternative forage source for lactating dairy cows that when fed to mid-lactation cows tends to improve the efficiency of conversion of feed to milk without altering milk production or milk composition.