Corn Oil Supplementation to Steers Grazing Endophyte-Free Tall Fescue. II. Effects on LM and S.C. Fatty Acid Composition and Stearoyl-CoA Desaturase activity and expression

¹ University of Georgia, Athens
² Clemson University, Clemson, SC 29634-0311

^* To whom correspondence should be addressed. E-mail: sducket{at}clemson.edu.

	Abstract

Eighteen steers were used to evaluate the effect of supplemental corn oil level to steers grazing endophyte-free tall fescue on fatty acid (FA) composition in LM and s.c., stearoyl Co-A desaturase (SCD) activity and expression in s.c., and adipose cellularity in s.c. Corn oil was supplemented at 0 (NONE), 0.75 (MED) and 1.5 (HI) g / kg of BW. Cottonseed hulls were used as a carrier for the corn oil and supplemented according to pasture availability (0.7 to 1% BW). Steers were finished on a rotational grazed tall fescue pasture for 116 d. Fatty acid (FA) composition was determined by GLC. Fatty acid intake was analyzed as a complete randomized design and tissue fatty acid profile as a split-plot design using the MIXED procedures. Linear and quadratic oil effects were tested. Total linoleic acid intake increased linearly (P < 0.01) with corn oil supplementation (90.7, 265.1 and 406.7 g in NONE, MED and HI, respectively). Oil supplementation linearly reduced (P < 0.05) myristic, palmitic and linolenic acid percentage in LM and s.c. Vaccenic acid (C18:1 t11; VA) percentage was 46% and 32% greater (Linear, P = 0.02; Quadratic, P = 0.01) for MED and HI, respectively, than NONE regardless of tissue. Effect of oil supplementation on CLA cis-9, trans-11 was affected by adipose tissue (P < 0.01). In the LM, CLA cis-9, trans-11 isomer was 25% greater for MED than for NONE, and intermediate for HI; whereas CLA cis-9 trans-11 CLA isomer was 48 and 33% greater in s.c. adipose tissue for MED and HI than for NONE, respectively. Corn oil linearly increased (P 0.01) trans-10 octadecenoic acid and CLA trans-10, cis-12; however, values were low (< 0.35% and < 0.035% of total fatty acids, respectively). Oil supplementation did not change (P > 0.05) the percentage of total SFA, MUFA, or PUFA but linearly increased (P = 0.03) n-6:n3 ratio from 2.4 to 2.9 in NONE and HI, respectively. Among tissues, total SFA and MUFA were greater in s.c. than LM; whereas total PUFA, n-6, n-3 FA and the n-6: n-3 ratio were lower. Trans 10 octadecenoic acid, VA, and CLA trans 10, cis 12 were greater (P < 0.01) in s.c. than in LM. Oil supplementation did not alter (P > 0.05) stearoyl-CoA desaturase (SCD) activity or mRNA expression. Corn oil supplementation to grazing steers reduced the percentages of highly atherogenic fatty acids (myristic and palmitic acids) and increased the percentages of antiatherogenic and anticarcinogenic fatty acids (VA and cis-9, trans-11 CLA).

Key Words: Beef, Forage, Fatty Acid, CLA

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