Abstract In four experiments, lactating Holstein cows were used to evaluate the nutritive value of corn silages treated with organic acids. Propionic, formic, and acetic acid treatment of silage with medium dry matter (34 to 39%) in two experiments slightly increased silage intake but had little effect on milk yields. However, addition of propionic acid to silages with high dry matter (42 to 47%) in three experiments increased silage intake 12%, total intake 6%, and milk yields 5%. Formic acid added to high dry matter silages was less effective than propionic in increasing intakes. Decreasing dry matter of silage from 43% to 36% with water added at ensiling did not improve intakes or milk yields. Propionic treatment decreased silage temperatures during fermentation and feeding and lowered fungal counts of silage exposed to air. Normal concentrations of lactic and acetic acids and pH values resulted from propionic treatment. Propionic treatment of high dry matter silage appeared profitable.