This study examines ensiled rice straw (ERS) with three levels of prickly pear fruit peels (PPP, w/w), 100, 150, and 200 kg per ton rice straw (RS), and added 5 kg of urea. Corn stalks ensiled with 25 kg of  molasses per ton and 5 kg of urea was used as a control (CS). In a 4×4 Latin square experiment, 16 Ossimi rams (61.4±0.16 kg) were randomly assigned into four equal groups. The values of lactic acid, volatile fatty acids (VFA^,s) and lactic acid bacteria (LAB) count were significantly (P < 0.05) decreased with increasing PPP in ERS, while the values of pH and NH₃-N were decreased.
The values of VFAs and LAB count of ERS improved compared to CS, while pH and NH₃-N were decreased (P < 0.05). No mold was detected in the tested silages. While neutral detergent fiber (NDF), acid detergent fiber (ADF), and total carbohydrates (TCH) values were decreased in ERS with increasing levels of PPP, the ash was significant (P < 0.05)  increased. Dry matter recovery (DMR) values were (P < 0.05)  higher with ERS than CS. There was no difference among ERS in terms of PPP levels for cumulative gas production (GP) up to 72 hours of incubation. Increased IVOMD, IVNDFD, and IVCPD values were associated with increased (P < 0.05) feed intake of ERS. Digestibility of DM, OM, CP, NDF, and ADF increased (p < 0.05) with the increase of PPP in ERS; which was reflected in the increase of TDN and DCP. The increased PPP level in ERS increased N-retention (P < 0.05). The TVFAs, acetate, bacteria number, and protozoa were increased (P < 0.05) in the rumen of sheep with increasing PPP in ERS, while NH₃-N values were decreased. No significant differences were shown in globulin, ALT, and AST in sheep blood plasma, while glucose was increased (P < 0.05) with increasing PPP level in ERS. Also, the concentration of urea and creatinine were decreased. The values for hemoglobin, erythrocytes, white blood cells, and PCV followed the same trend. Fermentation characteristics of ensiled rice straw with the inclusion of PPP were improved and can be recommended as a feed source for sheep.