Finishing diets with elevated levels of alpha-linolenic acid increase feed efficiency and adipose lipogenesis but do not alter beef carcass quality.

Abstract

Forty-five Angus steers (358 kg BW) were utilized in a completely randomized block design with a 3 x 3 factorial arrangement of treatments to evaluate the hypothesis that differing dietary linolenic acid (from corn, flaxseed plus corn, or milo) and whole cottonseed (WCS) inclusion (0, 5, or 15% DM) would interact to alter fatty acid metabolism and deposition of conjugated linoleic acid (CLA) in subcutaneous (s.c.) and interfasicular (i.f.) adipose tissues, and thereby decrease carcass quality score. During the feeding period (135 d), steers receiving flaxseed or corn diets had a greater gain:feed ratio (0.119 and 0.108, respectively) than steers receiving the milo diet (0.093). Following transportation to a local abattoir and overnight starvation, there was less decrease in weight in flaxseed-fed steers (1.51%) than in steers fed the corn (2.89%) or milo diets (3.11%). Ribeye area of steers fed milo was less than that of steers fed the corn or flaxseed diets. Lipogenesis from acetate in s.c. adipose tissue was greater in steers fed flaxseed (5.42 nmol h-1 105 cells-1) than in the corn (3.10 nmol h-1 105 cells-1) or milo (1.92 nmol h-1 105 cells-1) groups. Stearoyl-CoA desaturase (SCD) activity in s.c. adipose tissue was unchanged between the 0% WCS group (88.1 nmol mg protein-1 7 min-1) and the 15% WCS group (20 nmol mg protein-1 7 min-1). The i.f. saturated fatty acid percentages increased with increasing levels of WCS. The i.f. cis-9, trans-11 CLA percentage increased with increasing WCS in the steers fed the corn diet, whereas it remained unchanged or even decreased slightly in the steers fed the flaxseed or milo-based diets. Steers fed flaxseed had a greater s.c. adipose concentration of vaccenic acid (18:1trans-11) than the steers fed milo. Steers fed flaxseed also had greater s.c. and i.f. percentages of linolenic acid (18:3, n-3) than steers fed either of the other grain sources. Increased dietary linolenic acid from flaxseed may have increased s.c. adipocyte volume by stimulating lipogenesis. These data indicate that rations formulated to provide increased levels of linolenic acid (i.e., flaxseed) will increase feed efficiency and lipogenesis from acetate without altering either the quality or composition of the beef carcasses.