A total of 66 post-weaned rabbits (35th day of age meat line M91 a P91 hybrid) were randomly divided into 3 groups for fattening experiment, kept in standard metal cages with two animals per cage. Rabbits were fed with commercial diet (control group, CG), or supplemented with 5% of agricultural by-products linseed cake (EG1), or supplemented with 10% linseed cake (EG2). The experiment lasted 42 days, until the animals attained the slaughtering weight ≈2.5 kg. Individual blood was sampled from a total of 30 rabbits, and five animals from each group were slaughtered at the end of experiment, for the evaluation of animal welfare and meat quality. Feeding of linseed cake substances in rabbits did not negatively influence zootechnical parameters, growth performance and slaughter traits; it had no negative effect on rabbit’s blood biochemical profile either. Experimental diets with 5% linseed cake improved feed conversion ratios, without significantly impacting the final weight of animals. The dietary supplementation positively influenced the meat fatty acids profile, in particular polyunsaturated fatty acids (linoleic acid and CLA), indicating enhanced nutritional quality of the meat as a functional food. Overall, the use of linseed cake, a sustainable agricultural by-product, is a promising dietary strategy to improve the nutritional value of rabbit meat and support efficient, welfare-conscious rabbit production.