<p>Fatty acids are a diverse group of lipid molecules that play essential roles in energy metabolism, cellular differentiation and signalling mechanisms. The objective of this study was to explore the genetic determinism of fatty acid composition across backfat, liver, muscle and plasma and its association with immunocompetence and performance traits in pigs. Fatty acid profiles were analysed in 432 commercial Duroc pigs. High heritability was found for most fatty acids in backfat and for long-chain polyunsaturated fatty acids in liver, while muscle and plasma showed medium to low heritabilities. Strong genetic correlations were observed between the relative abundance of γδ T cells and cytotoxic T cells with the lipid profiles of backfat and muscle, with opposite patterns between these cell types. Muscle unsaturated fatty acids were positively correlated with phagocytosis capacity and red blood cell traits, and negatively with plasma cortisol. Acute phase proteins showed similar correlations with liver lipids but opposite with some plasma fatty acids. Lean meat and fatness traits were particularly associated to the backfat fatty acid composition, showing opposite correlation patterns, while pH was strongly correlated with the liver fatty acid profile. These results demonstrated the specific lipid profiles of backfat, liver, muscle and plasma, their genetic determinism, and their relationships with immunity and production traits.</p>