Bovine serum lipids. II. Lipoprotein quantitative and qualitative composition as influenced by added animal fat diets.

S ERUM lipoproteins have been studied in some detail in relation to certain disease conditions and metabolic disorders of man. However, very limited research has been conducted on the lipoproteins of ruminant animals. Current research in ruminant nutrition and metabolism has focused more attention on lipid utilization and its interactions with proteins in the serum. Researchers (Evans, Patton and McCarthy, 1961; Berry et al., 1963; Glascock et al., 1966; Welch et al., 1968; Moore, Steele and Noble, 1969a) have demonstrated apparent lipoprotein specificities in lipid transport as well as fatty acid utilization by mammary tissue in ruminant animals. However, these researchers have not measured the concentrations of the different serum lipoprotein fractions nor have they determined whether or not the lipoprotein separations based on human lipoprotein fraction densities contain the major individual groups of the llpoproteins which may be metabolically important. Such a fractionation study has been conducted with pig serum (Janado, Martin and Cook, 1966) and it was determined that the low density lipoprotein fraction had two clearly resolvable components. The fatty acid composition of certain lipoprotein fractions of the lactating bovine have been reported by Evans et al. (1961) and McCarthy et al. (1968). McCarthy, Porter and Griel (1968) observed somewhat severe alterations in the serum lipoproteins of cows with ketosis and also in animals with depressed milk fat. Studies by Berry et al. (1963) demonstrated that a significant portion of the milk fats from ruminant animals are carried in the bloodstream by the low density lipoproteins. In this study, the serum lipoproteins of maturing beef steers fed ad libitum, a high energy finishing ration, were studied in relation to the characteristics of the lipoprotein frac-