AbstractMown herbage of timothy–meadow fescue (dry matter 218 (LDM) or 539 (HDM) g kg−1) was ensiled in laboratory silos to evaluate silage additives. For LDM silage, additives including formic acid (a blend of formic acid, sodium formate, propionic acid, benzoic acid, glycerol and another blend of formic acid and ammonium formate, both applied at 5 L t−1) were able to restrict fermentation and thereby improve intake potential of the silage. Aerobic stability (AS) of total mixed ration (TMR) was also improved. LDM grass treated with homofermentative lactic acid bacteria (hoLAB) resulted in silage containing lactic acid at 132 g kg−1 DM, ammonium‐N <40 g kg−1 total N, and pH < 3·8, and the AS was poor (<36 h). The treatment including heterofermentative strain (Lactobacillus brevis) produced more acetic acid and better AS than hoLAB. Salt treatment (sodium benzoate, potassium sorbate, sodium nitrite) reduced pH compared to the Control treatment (3·89 vs. 4·24) and improved AS of TMR. The LDM Control silage had good AS, but the TMR based on it had poor AS. All additives were able to lower pH on HDM silages also, but other benefits of using additives were minimal. The treatment including L. brevis on HDM was able to improve AS of TMR.