2016 Elsevier Ltd. All rights reserved. The fatty acid composition of carcass tissues significantly influences the functionality of lipids used in processed and/or rendered products. In lean trim, fat can be either intramuscular (marbling) fat, intermuscular (seam) fat, or subcutaneous fat. Oleic acid is the most abundant fatty acid in the fat tissues of meat-bearing animals. Ingestion of the essential, polyunsaturated fatty acids, linoleic and -linolenic acids, by livestock species leads to enrichment of these fatty acids in fat depots. Because polyunsaturated fatty acids are extensively hydrogenated in the rumen, their levels are very low in carcass fat and lean trim of cattle, sheep, and goats. Porcine fat can be highly enriched with polyunsaturated fatty acids, as dietary polyunsaturated fatty acids are absorbed largely intact. In ruminants, de novo fatty acid synthesis, elongation, and desaturation account for most of the fatty acids in fat depots. In nonruminants, polyunsaturated fatty acids from dietary sources can contribute more than 10% of fatty acids in carcass tissues. Conjugated linoleic acid (CLA) is produced from the isomerization of polyunsaturated fatty acids by rumen microorganisms, but the concentration of CLA isomers in adipose tissue is less than 2% of total fatty acids. Stearic acid absorbed from the small intestine is at least in part desaturated to oleic acid in intestinal mucosal cells, before distribution to the circulatory system. The concentration of stearic acid in lipids has the greatest effect on lipid melting points, which can be from less than 30. C in lipids from fat of pigs or Japanese cattle to over 40. C in fat of sheep and pasture-fed cattle. The relative concentrations of saturated, monounsaturated, and polyunsaturated fatty acids affect the quality and stability of processed products and rendered fats.