Farm Animal Metabolism and Nutrition

Chapter 5

Lipid Metabolism

J.K. Drackley

Department of Animal Sciences, University of Illinois,

Urbana, Illinois, USA

Introduction

Traditionally, the study of lipid absorption
and metabolism in farm animals has
centred on the role of dietary lipids in
provision of dietary energy and in
processes of fat deposition in meat, milk
and eggs. Interest in these areas remains
intense because of the importance of fat
deposition in determining the efficiency
and, hence, profitability, of meat and milk
production. The content and composition
of fat in animal products has become
increasingly important to consumer per-
ceptions of the healthfulness of meat and
milk. Although a normal part of animal
growth or milk synthesis, fat synthesis
decreases the efficiency of conversion of
feed nutrients into lean meat or low-fat
milk products that consumers desire.
Furthermore, metabolism of lipids in the
liver is an integral component of animal
production and is a key factor in develop-
ment of metabolic disorders such as ketosis
and fatty liver. Consequently, this chapter
will focus primarily on aspects of diges-
tion, absorption and transport of dietary
lipids, lipid synthesis, lipid mobilization
and lipid metabolism in the liver.

In addition to the primary and well-

studied roles of lipids as energy substrates,

however, many new roles of lipids as

biological mediators and second messengers

in processes of signal transduction have

been discovered in recent years. An

overview of these functions will also be

presented.

Digestion, Absorption and Transport

of Dietary Lipids

Digestion and absorption of

lipids in non-ruminants

Lipids consumed by non-ruminant animals

are predominantly triacylglycerols (tri-

glycerides), with the exception of herbi-

vorous animals such as horses and rabbits

that may consume considerable amounts of

galactolipids from vegetative material.

Proteolytic activity in the stomach helps to

release lipids from feed matrices, and the

acid conditions and churning activity

caused by gastric motility serve to disperse

the lipids into a coarse emulsion. Lipase

activity is present in the stomach, which

may arise from enzymes synthesized and

© CAB International2000. Farm Animal Metabolism and Nutrition

(ed. J.P.F. D’Mello) 97