The present study was designed with two primary objectives: (1) to investigate and compare the effects of different rearing systems—specifically intensive versus extensive production—on the quality characteristics of loins obtained from Bísaro pigs, a traditional Portuguese breed, and (2) to assess the potential influence of dietary supplementation with olive cake, a by-product of olive oil production, on the physicochemical composition of pork loins derived from these animals. To achieve these aims, muscle samples from the Longissimus thoracis et lumborum region were collected from Bísaro pigs reared on farms located in the Trás-os-Montes region of northern Portugal. The slaughter and carcass cutting procedures were standardized and conducted at the Bragança municipal slaughterhouse, ensuring consistency in sample handling and preparation for laboratory analyses. Comprehensive evaluation of physicochemical parameters revealed that, among the various components analyzed, only the ash content showed a statistically significant difference (p = 0.007) between the two rearing systems, suggesting that farming conditions may influence mineral content in the meat. However, no statistically significant differences (p > 0.05) were observed between rearing systems concerning other key quality indicators, including moisture content, protein concentration, total fat, collagen content, and pigment levels. Furthermore, the inclusion of olive cake in the animals’ diet, regardless of the rearing system employed, did not result in any significant alterations in the levels of these physicochemical traits. The same lack of statistical significance (p > 0.05) was observed in the analysis of the meat's fatty acid composition, including the proportions of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs).