Thirty-six Dorper x Santa Ine circumflex accent s ewe lambs with an initial age of 4.7 +/- 0.5 months (mean +/- SD) and initial weight of 27.9 +/- 4.3 kg (mean +/- SD) were assigned to a randomized complete block design. This study was designed to evaluate the effects of including a propionic acid-based ad-ditive with surfactant action during the ensiling of rehydrated corn grain on its nutritional value and animal performance. Ground dry corn was rehydrated to reach 400 g/kg fresh matter of moisture, with or without additive, and ensiled in 200-L plastic drums. The treatments were prepared as follows: rehydrated corn grain silage (RCGS) stored for 50 d as a negative control (50CON), RCGS stored for 90 d as a positive control (90CON) and RCGS treated with MycoflakeTM at 2 L/t and stored for 50 d (50MYC). A basal total mixed ration containing 200 g/kg sugarcane bagasse, 600 g/kg RCGS (according to treatment), 160 g/kg soybean meal, 5 g/kg urea, 20 g/kg limestone and 15 g/kg mineral in total diet dry matter (DM) was offered to the animals. The trial was divided in two subsequent periods of 28 d each in order to organize samplings and pro-cedures with the animals and to evaluate RCGS condition over time. Ruminal DM disappearance (DMD) of RCGS was evaluated in situ using two canulated Holstein cows after 12, 24 and 48 h of incubation. The extended storage time of 90CON silage increased soluble protein (SP; P = 0.01) and NH3-N contents (P = 0.03) and the ruminal DMD. Although no change in SP content was observed for the 50MYC silage, its NH3-N content was higher than for the 50CON silage (P = 0.02), and its proportion of NH3-N in soluble N was the highest among the treatments (P < 0.01). The 50MYC silage presented the lowest concentrations of lactic acid (P < 0.01), and also yielded the lowest contents of ethanol (P < 0.01) and butyric acid (P = 0.02) in relation to the control silages. There were no changes on ruminal DMD for the silage treated with MycoflakeTM against the 50CON silage, except for a decrease in the soluble fraction only in the second feeding period (P = 0.01), and a higher undigested fraction after 48 h of incubation compared to both control silages (P = 0.02). There was no effect of storage time or additive on dry matter intake, body weight gain and feed efficiency of the ewe lambs. The silage treated with the additive also did not change the selective behavior of the animals. The results suggest that MycoflakeTM seems to promote a delay in the protein matrix degradation even with extended storage times, and that it may have potential as an additive for conservation of RCGS.