Fatty Acid Composition of Backfat, Intermuscular, KPH and Tail Fat Depot Sites of Angus Steers Finished on Grass or High Grain Diet

Ruminant protein has been shown to have high nutrient value because of its essential amino acid, vitamin and mineral composition (Williamson et al., 2005; Biesalski, 2005). The U.S. Food and Drug Administration (FDA) states that approximately 60% of saturated fatty acid is derived from animal fat composed mainly of palmitic acid (C16:0) and stearic acid (C18:0). Stearic acid has no impact on raising serum cholesterol in humans (Biesalski, 2005; Yu et al. 1995). Moreover, 30% of the fatty acid content produced by beef cattle consists of the MUFA oleic acid (C18:1) (Whetsell et al., 2003), which has been shown to reduce cholesterol levels, the risk of strokes, heart disease and high blood pressure in predisposed populations (Kris-Etherton, 1999). Therefore, besides understanding the effects of diets on fatty acid profile, knowledge in the distribution of fatty acids throughout the animal carcasses is important for a better understanding of fat deposition, order of adipose tissue accretion and use of some fatty acids as metabolizable energy during the growth phase.;This study compares fatty acid profile of backfat, intermuscular fat, KPH and tail fat depots among animals finished on a grass or a grain based diet at similar quality grades. Thirty-two Angus steers (15-mo of age) were obtained from a local ranch (Yolo Land and Livestock Cattle Company). Fourteen were transported to the University of California, Davis feedlot and 18 remained on the ranch. During the finishing phase, grass finished steers stayed on average 10-mo on irrigated pasture, which consisted of ryegrass and white clover (CP= 15.1% and ME= 2.58 Mcal/kg DM). Grain finished steers were fed a finishing diet based on cracked corn (CP= 11.5% and ME= 2.83 Mcal/kg DM), for 4 months. Fat depots from grass finished animals contained higher percentages (P<0.01) of C6:0 (caproic acid), C12:0 (lauric acid), C14:0 (mystiric acid), C16:0 (palmitic acid) and C20:0 (arachidic acid). Grain finished steers had higher percentages of C18:0 (stearic acid) and C18:3 (n-3 fatty acid) as compared to grass finished steers (P <0.01). Percentages of C18:1 trans9, C18:2 cis9 cis12 and C18:2 trans9 trans12 were higher in grass finished steers compared to grain with 1% level of significance (P<0.01). C18:0 content was greater and C18:1 content was lower in the KPH region (inner fat depot) as compared to outer fat depots (P<0.05). CLA content was 1.6 times greater in the grass finished group, which agreed with previous studies in which CLA content of grass finished beef was approximately 2 times greater than that of grain finished beef.