The study evaluated the effects of feeding strategies on growth performance, health laboratory biomarkers, and antioxidant protection of slow-growing pigs, fed finisher diets containing alternative protein sources (local and by-product), as an element of sustainable pig production. The study involved 40 fattening pigs (Pulawska native breed), fed the same grower mixture, while dietary treatment was applied during the finisher phase (90–135 kg BW). The diet in all groups was isoenergetic and isoprotein, but differing in additives. Control pigs—mixture without additives; experimental groups—feed supplemented with 3% flaxseed together with 2% dried herbs (H), or 2% dried fruit (F), or 2% herbs with dried beetroot (HB). The experimental finisher diets did not change the fattening results, carcass, and physico-chemical traits of meat quality. Summarized, the tested feeding strategies can be proposed for the production of native (local) pork with higher PUFA n-3 and dietetic added value combined with the oxidative stability of the meat, with the diet containing flaxseed together with dried herbs proving particularly effective for inhibiting the negative effects of oxidative stress in pigs (higher CAT, SOD, GSH and lower MDA, LOOH observed in blood and meat, p ≤ 0.05), and improving their immune blood indices (higher IgA, IgG, IgM, lysozyme, lower Il6 and Il8, p ≤ 0.05).