Date of Award

8-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Animal and Veterinary Sciences

Advisor

Jenkins, Thomas C

Committee Member

Bridges , William C

Committee Member

Duckett , Susan K

Committee Member

Powell , Gary L

Abstract

Pathways of docosahexaenoic (DHA) biohydrogenation are not known; however, DHA is metabolized by ruminal microorganisms. The addition of DHA to the rumen alters the fatty acid profile of the rumen and milk and leads to increased trans-18:1 isomers, particularly trans-11 18:1 and 22 carbon fatty acids. This study included four in vitro experiments to identify if these are produced from DHA or if they come from other sources that are affected by DHA. In each experiment, ruminal microorganisms collected from a lactating Holstein cow were incubated in batch cultures for 0, 6, 24, and 48h and a uniformly 13C DHA was added to the cultures at 0 h as a metabolic tracer. In all experiments, any fatty acid that was enriched with the 13C label was determined to arise from DHA. In chapter 1, palmitic (C16:0), stearic (C18:0), all trans-18:1, eicosanoic (C20:0), and docosanoic (C22:0) acids were examined for enrichment. Chapter 1 included 2 experiments utilizing 10ml batch cultures that examined 0, 0.5, 1, 2, and 3% DHA supplementation to determine if DHA is converted into trans-18:1 and if the level of DHA effected its conversion into trans-11 18:1. Trans-18:1 isomers increased 254, 185, 256, and 272% from 0 to 48 h when DHA was supplemented at 0.5, 1, 2, and 3%, respectively; however, there was no label in trans-18:1 at any time. Docosanoic acid was highly enriched at 24 h and 48 h to 20.2% and 16.3%. Low levels of enrichment were found in palmitic and stearic acids. Enrichment of docosanoic acid decreased linearly with increased DHA supplementation. Chapter 2 studies utilized 25ml batch cultures with 0, 0.5, and 1% DHA to examine unsaturated 22 carbon fatty acids. In 0.5% DHA cultures, up to 2 isomers of C22:5, 4 isomers of C22:4, 5 isomers of C22:3, and 5 isomers of C22:1 were isolated in 6, 24, or 48h cultures. In 1% DHA cultures, up to 5 isomers of C22:5, 6 isomers of C22:4, 5 isomers of C22:3, and 3 isomers of C22:1 were isolated in 6, 24, or 48h cultures. No isomers of unsaturated 22 carbon fatty acids were isolated from cultures when DHA was not added. Over time, the isotope profiles changed from 55% C22:5 at 6h to 35% C22:3 and 29% 22:1 at 48h. All of the 22 carbon unsaturated fatty acids contained the 13C label indicating that they are produced from DHA. These experiments indicate that DHA is not converted into C18:1 fatty acids but is hydrogenated to 22 carbon fatty acids.

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