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Composition of Bovine Milk as Affected by Intravenous Infusion of Sunflower Oil. Fixation of Milk Fat for Electron Microscopy

Department of Food Science, University of Guelph, Guelph, Ontario, Canada

ABSTRACT

A stable, nontoxic, 15% sunflower oil emulsion containing 65% linoleic acid was formulated for intravenous infusion into a cow. An infusion of 500 ml of this emulsion into a Jersey cow caused a parallel increase in the fat and protein of the milk and a decrease in lactose. The correlations obtained, between the percentages of fat-protein (morning's milk, r = 0.99; evening's milk, r = 0.85), and fat-lactose (r = –0.71) and yields of fat-protein (r = 0.98) and fat-lactose (r = 0.98) indicated the existence of some control mechanism in the cow, relating fat, protein, and lactose synthesis. There was an increase of 5% in linoleic acid at the second post-infusion milking. Consequently, the unsaturation of the milk fat was increased which, in turn, improved its fixation by osmium tetroxide for electron microscopy. The appearance of large extraalveolar fat droplets, 3 to 85 µ in diameter, and the prolonged effect of the infusion on the milk fat composition is indicative that the emulsion was cleared from the blood stream and stored as milk fat precursors until they could be used in the formation of milk fat by the secreting alveolar cells.