Sustainability is a hotly debated topic, and the livestock sector is consideredone of the most important contributors to global warming. The use of by-products as animal feedis beneficial both socioeconomically and ecologically. Prickly pear (Opuntia ficus-indicaL. Mill) iswidely grown in the arid regions of multiple continents, and its by-products can be used as ruminantfeed, but their seasonality and chemical properties pose several problems for their preservationand utilization. Ensiling could be the optimal preservation technology. In this study, the chemicalcomposition, nutritional properties, polyphenols, antioxidant activity, and mineral content of pricklypear by-products were evaluated for their persistence after ensiling. It was found that prickly pearby-products are a low-cost and suitable raw material for ensiling; peel silage and "pastazzo" (peel,pulp, and seeds) silage exhibits optimal pH and organic acid content, high polyphenol content, andantioxidant activity and appears to be a source of minerals. Italy is the third largest producer of Opuntia fruits in the world after Mexico and the United States, and 97.72% of these fruits produced by Italy are grown in Sicily. The use of prickly pear fruits or juice leads to a high production of by-products. In this study, ensiling was chosen to preserve prickly pear peels (PPPs) and "pastazzo" (PPS) mixed with 12% wheat bran. PPP silage presented a lower DM than PPS silage (20.03 vs. 41.37%; p < 0.01), as well as aNDFom (25.31 vs. 66.66% DM; p < 0.01), but had the best protein content (12.02 vs. 9.55% DM; p < 0.01). For both by-products, fermentation proceeded rapidly with increasing temperature, with the temperature for PPS (38 degrees C) being higher than that for the PPP (30 degrees C). Mesophilic LAB (lactic acid bacteria) were detected at higher levels than thermophilic LAB, and rod counts were higher than cocci counts. The detected organic acids and silage pH indicate an optimal fermentation process for these by-products. PPP silage had a higher polyphenol content than PPS silage (30.24 vs. 24.22 mg GAE/g DM; p < 0.01) and, consequently, also higher antioxidant activity. The results of this study on the mineral composition and macro- and micro-nutrients in silage highlight that these by-products are sources of minerals, with high levels of potassium, calcium, and magnesium.