The purpose of this study was to investigate the effects of valorizing corn straw as an alternative feed for fattening calves by treating it with ammonia gas. Different levels of ammonia gas (AG) (0, 2, 3, and 4%) were injected into bags containing moistened corn straw. The plastic bags were stored at 20-25 °C for one month. The results showed that corn straw processed with 4% AG, compared to other experimental treatments, increased the amount of protein (P<0.05). Corn straw treated with 3% AG increased the amount of ether extract compared to the untreated group (P<0.05). Corn straw processed with 3% and 4% AG reduced acid detergent fiber (ADF) (P<0.05). Corn straw treated with 4% AG reduced neutral detergent fiber (NDF) compared to the control group. Additionally, the NDF of corn straw was reduced by using a 3% level of AG (P<0.05). Corn straw treated with 4% AG significantly improved the digestibility of organic matter (% DOM), digestibility of organic matter in dry matter (% DOMD), and metabolizable energy (ME) (P<0.05). Corn straw treated with 4% AG increased gas production at 6, 12, 48, and 72 hours of incubation, but no significant difference was observed at 24 and 36 hours of incubation. Nutritional parameters results of gas production (digestibility of organic matter (OMD), ME, and short-chain fatty acids (SCFA) were not affected by processing with ammo-nia gas. The highest feed intake was recorded with processed corn straw at 9.108 kg, while the feed conversion ratio remained stable, indicating no significant improvement in weight gain efficiency. Total feed costs were lowest for calves without corn straw at $176.320, with minimal increases for unprocessed and processed corn straw options, highlighting the economic considerations of incorpo-rating corn straw into feeding strategies. In general, it can be concluded that treating corn straw with 4% ammonia gas improves its nutritional value by enhancing protein content and digestibility. Despite the increased feed intake, feed conversion efficiency remained unchanged, suggesting economic ad-vantages in calf feeding strategies. پرونده مقاله