D.L. Palmquist

Biosynthesis of conjugated linoleic acid in ruminants and humans.

Publisher Summary This chapter discusses the biosynthesis of conjugated linoleic acid (CLA) in ruminants and humans. Conjugated linoleic acid is a mixture of positional and geometric isomers of linoleic acid with a conjugated double-bond system. Because of its potential to improve human health, there is great interest to increase the amount of CLA in the human food supply. This has caused great effort to be expended toward increasing the concentration of CLA, and more specifically rumenic acid (RA), in the milk and tissues of ruminant foods because these are the predominant source of CLA in human diets. RA is the predominant CLA isomer present in ruminant products, and the major source of its occurrence is endogenous synthesis via desaturation of vaccenic acid (VA) by ∆-9-desaturase. The chapter focuses on improving the understanding of biohydrogenation in the rumen and examining milk and tissue CLA responses to a range of diets. The diversity of various BH intermediates in digesta, milk, and tissues indicates the complexity of the BH processes as a whole and the population dynamics of the ruminal bacteria involved. Predicting the outcome of changes in the diet is complicated by the interactions of the ruminal environment, substrate supply and forms of dietary lipids, all of which influence the BH process simultaneously.

The Role of Dietary Fats in Efficiency of Ruminants

Fat increases energetic efficiency in lactating cows by increasing total energy intake, by generating ATP more efficiently (ATP/unit energy expended) than volatile fatty acids or protein, by direct incorporation into product, and by promoting nutrient partition toward milk production. Factors that limit utilization of large amounts of fat by ruminants include inhibitory effects on ruminal fermentation, lower intestinal absorption at high intake, low contribution to total oxidation of nutrients, and sensitivity to nutrient imbalance, causing reduced energy intake. Research has resolved many problems associated with effects on ruminal fermentation; research in the future may improve fat digestibility and reduce limits of oxidation. Effect of high fat on regulation of feed intake has received little attention.

Chylomicron fatty acid composition and serum lipid concentrations in subjects fed carpenin or palm oil/palm kernel oil as the major dietary fat

This study, part of a larger study of dietary fats with different saturated fatty acid content, was performed to investigate the effect of caprenin on chylomicron fatty acid composition and postprandial serum lipid concentrations. Caprenin is a triglyceride made of caprylic acid (8:0), capric acid (10:0) and behenic acid (22:0). Thirty subjects were standardized for 3 weeks on a diet providing palm oil/palm kernel oil (POPKO) as the major fat in a 38 energy % fat diet. Then, 15 subjects continued eating POPKO while 15 switched to caprenin. After 5 weeks subjects consumed a meal with 40 g of test fat; blood was sampled at 0, 2, 4 and 6 hours. Amounts of 22:0 but not 8:0 and 10:0 varied (P<0.05 for time effect) over the 6 hour period in caprenin subjects; proportions of these fatty acids were much lower in chylomicrons than in the caprenin meal while proportions of palmitic acid (16:0) and oleic acid (18:1) were at least 4-fold higher in chylomicron lipids than in the meal. Postprandial concentrations of triglycerides in chylomicrons and serum and of cholesterol in plasma did not differ between dietary groups. These findings indicate 1) very low uptake of 8:0, 10:0 and 22:0 into chylomicrons, 2) a postprandial lipemia after caprenin comparable to that produced by other dietary fats as opposed to a fat-free meal, 3) considerable contribution of endogenously-derived fatty acids to chylomicron lipids and 4) equal effects of saturated fatty acids on pre- and postprandial concentrations of plasma cholesterol.

A 100-Year Review: Fat feeding of dairy cows

Over 100 years, the Journal of Dairy Science has recorded incredible changes in the utilization of fat for dairy cattle. Fat has progressed from nothing more than a contaminant in some protein supplements to a valuable high-energy substitute for cereal grains, a valuable energy source in its own right, and a modifier of cellular metabolism that is under active investigation in the 21st century. Milestones in the use of fats for dairy cattle from 1917 to 2017 result from the combined efforts of noted scientists and industry personnel worldwide, with much of the research published in Journal of Dairy Science. We are humbled to have been asked to contribute to this historical collection of significant developments in fat research over the past 100 years. Our goal is not to detail all the work published as each development moved forward; rather, it is to point out when publication marked a significant change in thinking regarding use of fat supplements. This approach forced omission of critically important names and publications in many journals as ideas moved forward. However, we hope that a description of the major changes in fat feeding during the past 100 years will stimulate reflection on progress in fat research and encourage further perusal of details of significant events.