This study investigated the nutritional, energetic, and mineralogical implications of replacing conventional maize with underutilized agro-industrial by-products in livestock rations. A 100% maize control diet (MFF) was evaluated against three experimental diets where maize was replaced at a 50% inclusion level with Irish potato peel meal (MPF), yam peel meal (MYF), or cassava peel meal (MCF). The partial substitution preserved total organic matter density across all formulations (>90%). However, the higher concentration of structural non-starch polysaccharides inherent to root and tuber epicarps significantly reduced carbohydrate and caloric delivery (p < 0.05). Nitrogen-free extract (NFE) decreased from 47.42% (control) to 38.92% (MYF), 38.05% (MCF), and 35.47% (MPF). The reduction in digestible carbohydrates led to a decrease in calculated metabolizable energy (ME) profiles, which fell from 10.43 MJ/kg (MFF) to 9.62 MJ/kg (MYF), 9.50 MJ/kg (MPF), and 8.72 MJ/kg (MCF) due to the dilution of physical fiber. Conversely, the incorporation of tuber wastes resulted in a substantial natural increase in the concentration of essential minerals. Potassium accumulated significantly in MPF (0.97%) and MYF (0.53%), while calcium surged from 28.47% (control) to peaks of 68.67% (MPF) and 65.63% (MYF). Magnesium uniformly exceeded 81% across all test groups, alongside prominent accumulations of iron and zinc. However, phosphorus was significantly depressed in the cassava peel group (MCF: 9.37%), altering optimal dietary Ca/P ratios. Ultimately, replacing 50% of maize with root crop by-products offers a viable strategy for maintaining organic matter stability and enhancing mineral content, as long as targeted micronutrient balancing is applied for sustainable feed production.