Subcutaneous adipose fatty acid profiles and related rumen bacterial populations of steers fed red clover or grass hay diets containing flax or sunflower seed.

Yearling steers were fed 70:30 forage:concentrate diets for 205 days, with either grass hay (GH) or red clover silage (RC) as a forage, and concentrates containing either sunflower-seed (SS) or flaxseed (FS), each providing 5.4 % oil to the diets. Feeding diets containing SS compared to FS elevated (P<0.05) the subcutaneous proportions of trans (t)-18:1 isomers chiefly vaccenic acid (VA), conjugated linoleic acids, chiefly rumenic acid (RA) and n-6 polyunsaturated FA (PUFA), particularly linoleic acid (LA). Both forage and oilseed type influenced the subcutaneous proportions of total n-3 PUFA, especially a-linolenic acid (ALA) and total non-conjugated diene biohydrogenation (BH) products (i.e., atypical dienes, AD), with diets containing FS as opposed to SS or GH as opposed to RC having greater (P<0.05) proportions. Of the 25 bacterial genera impacted by dietary treatment, 19 showed a correlation to a FA. Similar to previous reports member of the genus Clostridium were highest in percent abundance when levels of CLNA, and n-3 PUFA’s were found to be lowest in the subcutaneous fat indicating a role in BH. Several genera including Anerophaga, Fibrobacter, Guggenheimella, Paludibacter and Pseudozobellia were significantly increased in the rumen when low levels of VA were found in the backfat of animals. However, genera in this study, which show a positive correlation to increased BH products need to be tested to see whether these correlations are consistent under a variety of dietary compositions. Present results demonstrate achieving high and consistent levels of BH products in beef will require a multifactorial approach taking into consideration the type of PUFA in the diet, the non-oil fraction of the diet, the type and level of feed processing, and the role of rumen microbes.