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The Influence of Corn By-products in Beef Finishing Diets on Fatty Acid Composition of Various Adipose Sites

Study conducted by Dr. Stelzleni, Mr. (Dr.) Jacob Segers, Ms. Samantha Belanger, and Ms. Rebecca Kersey

The objective of this study was to evaluate the effects of dried distillers grains with solubles (DDGS), corn gluten feed (CGF), or soybean meal and ground ear corn (SBM) on various beef adipose locations. Thirty-six Angus crossbred steers were assigned to one of three feedlot diets differing in protein source included at 25% of the diet DM; 1) DDGS, 2) CGF, and 3) SBM and individually fed for 100 d. Steers were slaughtered when backfat was estimated at 1.27-cm via ultrasound. At 24-hr postmortem, tissue samples were collected from the Longissimus lumborum intramuscular fat (LL), subcutaneous fat from the Longissimus lumborum (SQ) and subcutaneous fat from the brisket region (BR) for fatty acid (FA) analysis. Total lipids were quantitatively extracted and FA content was determined by gas chromatography (Agilent Technologies, Santa Clara, CA). The MIXED procedure (SAS Inst. Inc., Cary NC) was used to test the main effects of adipose location, protein source and the subsequent interactions at α = 0.05. There was a protein source by adipose location interaction for percent of total saturated fatty acid (SFA; P = 0.03) and monounsaturated fatty acid (MUFA; P < 0.01), regardless of diet, BR had a decreased percentage of total SFA (P ≤ 0.01; 35.92%) and an increase percentage of total MUFA (P ≤ 0.01; 60.38%) compared to LL (46.67%, 46.80%, respectively) and SQ (45.60%, 50.44%, respectively).  Within protein source, the LL had a greater proportion of total polyunsaturated fatty acid (PUFA; P ≤ 0.01) than did BR and SQ, however, DDGS SQ was similar to CGF LL and SBM LL (P < 0.10). Regardless of protein source, BR had the lowest n-6:n-3 ratio (= 0.01; 3.32) compared to LL (9.39) and SQ (8.93). Dried distillers grains with solubles LL and SQ were similar to each other (P = 0.59) and greater than (P < 0.01) all other protein source by adipose location interactions. For conjugated linoleic acid (CLA), BR was greater than LL and SQ, independent of protein source (≤ 0.01). Furthermore, DDGS BR had a smaller proportion of total CLA compared to CGF BR and SBM BR (P ≤ 0.01). These results show that feeding corn by-products can differentially alter FA composition depending on adipose location.