Increasing pressure has been put on ingredient suppliers to assure a low level of oxidation, as measured by a low peroxide value. Our objective was to determine the effect of increasingly oxidized protein meals on the shelf life of extruded pet foods. Approximately one metric ton each of unpreserved chicken by-product meal (C) and unpreserved beef meat and bone meal (B) were collected and left unpreserved (U) or preserved with either ethoxyquin (E), or mixed tocopherols (T). These were allowed to oxidize at ambient conditions (25°C and 51% RH) while being monitored for peroxide value (PV) and anisidine value (AV) until they plateaued (41 and 63 d, respectively) at a PV of 88.44, 4.43, 2.22 mEq/kg and AV of 1.08, 0.55, 0.00 g/g for CU, CT, CE, respectively and at a PV of 86.42, 8.88, 2.23 mEq/kg and AV of 12.23, 7.14, 0.00 g/g for BU, BT, BE, respectively. Each meal was then incorporated into a model extruded cat food diet (~30% protein). Samples of kibble for each treatment were collected and stored at an elevated temperature and humidity (40°C and 70%) for 18 weeks. At time 0, PV and AV were greater for CU and BU (P < 0.05; 14.41, 10.07 mEq/kg and 15.56, 10.08 g/g, respectively) versus the preserved treatments CT, CE, BT, and BE (2.78, 2.22, 2.22, 2.22 mEq/kg and 3.85, 1.79, 9.62, 3.03 g/g, respectively). At elevated storage temperatures, the PV for CE remained low (4.44 mEq/kg), CT was intermediate (23.21 mEq/kg) and CU increased to 53.15 mEq/kg by 18 weeks (P < 0.05). The AV for C followed a similar pattern. The PV of B under elevated temperatures behaved differently; wherein, BE was low (3.33 mEq/kg), but BT had the highest PV (15.48 mEq/kg) and BU was intermediate (6.66 mEq/kg) by 18 weeks (P < 0.05). BE had the lowest (P < 0.05) AV and BT and BU were greater, but did not differ from each other (average 16.75 g/g) at 18 weeks. The results from this study demonstrate that oxidation occurred regardless of treatment; but, was rapid and extensive in meals without preservative. The ingredient oxidation levels were diluted by food production and their oxidation may not completely account for later food product deterioration.