Transcriptional Analysis in Longissimus thoracis Muscle, Subcutaneous and Kidney Fat of Cattle Fed Diets with Supplemental Flaxseed

Omega-3 fatty acids have been found to influence meat flavor and are beneficial to human health. Supplementation of livestock diets with flaxseed, a rich source of α-linolenic acid, is the most common means of producing omega-3 fatty acid-enriched animal products. Towards the goal of enhancing beef fatty acid composition, 64 crossbred cull cows (~30 months) with similar breed composition were randomized by weight/body condition, and fed 50:50 forage:concentrate diets on a DM basis (16 cows/treatment) containing ground barley grain with either hay or silage, supplemented with 0 or 15% ground flaxseed (DM basis). Five cows from each of the four diets were selected based on fatty acid profiles of the subcutaneous backfat collected at slaughter, after 140 days on the diet. RNA was isolated from Longissimus thoracis muscle, subcutaneous and kidney fat of each cow (20 samples/tissue) and hybridized in duplicate to BOMC 24K 60-mer microarrays. Differentially expressed genes were identified using linear modeling and the empirical Bayes approach within Limma to produce moderated t-statistics and associated p-values (Limma package, Biocoductor), incorporating the BH significance correction for multiple tests. Sixty-eight and 166 transcripts with p-value ≤ 0.05 and 0.10 respectively, were found to be differentially expressed in the three tissues combined of cattle supplemented with flaxseed compared to non-supplemented. From 166 transcripts, eight genes were identified to be associated with fatty acid metabolism using DAVID and PANTHER softwares. Selected differentially expressed genes from the microarray, plus other key genes/pathways important in fatty acid synthesis, were verified by real-time PCR.