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The objective of this study was to evaluate the inclusion of oregano essential oil (OEO) as a phytogenic feed additive in the diet of lambs on the productive performance, ruminal pH, ammoniacal nitrogen production, volatile fatty acids, nitrogen balance, carcass yield, backfat thickness, loin eye (Longissimus dorsi) area, shelf life, and antioxidant activity of the meat. Thirty-nine Suffolk × Hampshire lambs (19 ± 3.7 kg live weight) were used in a completely randomized design with three treatments (n = 13) consisting of 0, 0.02, and 0.04% OEO in the diet. The inclusion of OEO in the diet did not affect (p > 0.05) the productive performance due to the treatments; similarly, no differences (p > 0.05) were observed in the ruminal variables and nitrogen balance. Backfat thickness and loin eye area had similar results (p > 0.05), and the antioxidant activity in meat was improved (p < 0.05) with the inclusion of OEO. Shelf life and crude protein content increased (p < 0.05) with the inclusion of OEO in the diet and with the passing of storage days. Dry matter was affected (p < 0.05) by the storage time, with a decrease observed on day 24. pH, ether extract, and ash were not affected (p > 0.05). It is concluded that the productive performance, ruminal variables, nitrogen balance, loin eye area, backfat thickness, and carcass yield were not affected by the inclusion of OEO. However, crude protein remained stable and antioxidant activity improved, increasing the shelf life of lamb meat.