Systemic and Intracellular Trafficking of Long-chain Fatty Acids in Lactating Dairy Cattle
Stamey, Jennifer Anne
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Marine oils are used as ration additives to provide omega-3 fatty acids to dairy cows. Supplementing dairy cows with omega-3 fatty acid-rich feeds does not easily increase quantities in milk fat of dairy cows because polyunsaturated fatty acids are biohydrogenated in the rumen. Lipid encapsulation of omega-3 fatty acids provides protection from biohydrogenation in the rumen and allows them to be available for absorption and utilization in the small intestine. Lactating cows were supplemented with rumen protected algae biomass or algal oil in a 4 Ã 4 Latin Square. Feeding lipid encapsulated algae supplements increased docosahexaenoic acid content in milk fat while not adversely impacting milk fat yield; however, docosahexaenoic acid was preferentially esterified into plasma phospholipid, limiting its incorporation into milk fat. In the second study, triglyceride emulsions of oils enriched in either oleic, linoleic, linolenic, or docosahexaenoic acids were intravenously infused to avoid confounding effects of triglyceride esterification patterns in the small intestine and to compare mammary uptake. Milk transfer of fatty acids delivered as intravenous triglyceride emulsions was reduced with increased chain length and unsaturation. Increased target fatty acids were evident in plasma phospholipid, suggesting re-esterification in the liver. Transfer efficiencies were 37.8, 27.6, and 10.9Â±5.4% for linoleic, linolenic, and docosahexaenoic acid. Both liver and mammary mechanisms may regulate transfer of long-chain polyunsaturates. Intracellular fatty acid binding proteins (FABP) are cytoplasmic proteins that are hypothesized to be essential for fatty acid transport and metabolism by accelerating longchain fatty acid uptake and targeting to intracellular organelles, such as the endoplasmic reticulum for triglyceride esterification. FABP3 mRNA is highly expressed in bovine mammary and heart tissue, but is not present in MAC-T cells, a bovine mammary epithelial cell line. When overexpressed in MAC-T cells, FABP3 does not appear to be rate-limiting for fatty acid uptake in vitro and did not alter lipid metabolism. The function of FABP3 in the mammary gland remains unclear.
- Doctoral Dissertations