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Effects of Diet on Proportions of Blood Plasma Lipids and Milk Lipids of the Lactating Cow and Their Long-Chain Fatty Acid Composition^{1, 2,}

Department of Animal Sciences, Washington State University, Pullman 99163

ABSTRACT

The effect of three types of rations (all hay, hay-grain 50:50, and high grain) on changes in blood and milk lipids and their component long-chain fatty acids (LCFA) was studied in dairy cows in the last trimester of lactation. Jugular blood samples were drawn from 12 Holstein cows (4 in each treatment group) during Weeks 1, 5, 6, and 7 of the trial. Thin-layer chromatography and photodensitometry classified and quantitated blood lipids into triglycerides (TG), free cholesterol (FC), cholesterol esters (CE), free fatty acids (FFA), and phospholipids (PL). Gas-liquid chromatography determined proportions of LCFA methyl esters from C10 to C_20:4 in the total blood lipids.

There were no statistically significant differences in proportions of blood lipids between the three treatment groups at any stage of the experiment. Individual variations in their proportions between animals and within groups were large. Saturated LCFA comprised about 38% of the total LCFA of blood lipids, of which myristic, palmitic, and stearic acids were the major fatty acids. Ration did not significantly affect the proportion of any saturated LCFA of blood lipids. The bulk of blood fat was unsaturated LCFA and consisted of C₁₈ fatty acids (oleic, linoleic, and linolenic). Proportions of oleic acid were significantly higher (P < .05) in the blood lipids of cows receiving the all-hay ration during Weeks 5 and 7 as compared to those receiving either the hay-grain or high grain rations. The proportion of linoleic acid was lower and linolenic acid higher in the all hay group than in the other two groups.

There were no significant differences in milk fat per cent due to ration effects. Triglyceride, free cholesterol and phospholipid fractions did not vary significantly in milk fat, and the only fatty acid to show a consistent response to increased grain feeding was linoleic acid. This acid made up only 2.9 to 5.5% of the total fatty acid quantitated.

¹ Scientific Paper 3670, College of Agriculture Eesearch Center, Pullman, Washington. Project1439.

² Data reported are part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Doctor of Philosophy degree, Washington State University, Pullman.

³ Present address: Department of Nutrition, West Pakistan Agricultural University, Lyallpur.

⁴ Present address: Canada Department of Agriculture, Research Station, Agassiz, British Columbia, Canada.