We investigated changes in nitrogen metabolism and chemical, fatty acid (FA) and amino acid (AA) composition in tissues (longissimus dorsi (LD) and semitendinosus (ST) muscles, heart, spleen, liver and cecum) following the dietary addition of extruded linseed and walnut meal (50:50 mix). Plasma creatinine and urea nitrogen were determined as well. Two trials were designed using barrows (five replicates) allotted in two groups [(control, (SM) and experimental, (LEW))] in metabolic cages. The experimental diet rich in n-3 FA led to a significant increase of retained nitrogen (>8.09% in the LEW group). The biological value of feed protein was 14.8% higher in the LEW group than in the SM group. LD muscles from the SM group and liver from the LEW group had greater nitrogen contents, whereas the heart and spleen had lower concentrations of nitrogen in the LEW group. Diet had a pronounced effect on n-3 FA, particularly on α-linolenic fatty acid (ALA) (p < 0.0001). The highest levels of ALA were recorded in the cecum (>6.06 times in LEW) and heart (>5.44 times in LEW). The highest level of lysine was noticed in the LD muscle (>2.1% in SM). An n-3-rich diet significantly reduced the amount of nitrogen excreted; greater than 40% nitrogen was retained, thus improving the meat composition.
