It has been shown that the antifungal activity of silage acids can be better expressed by the amounts of undissociated acids on a water basis (Muck and O’Kiely, 1992). In this respect, total acids were considerably high in TMR silage, and the resistance to aerobic deterioration may be considered as that anticipated. However, the amount of undissociated acids was not necessarily higher in stable TMR silage than in labile corn silage. Therefore, other unidentified factors might be involved in the resistance of TMR silage in the presence of air.