Farm Animal Metabolism and Nutrition

Chapter 12

Use of Markers

J.P. Marais

Biochemistry Section, KwaZulu-Natal Department of Agriculture,

Pietermaritzburg, Republic of South Africa

Introduction

The productivity of animals and ultimately
the profitability of farm animal enterprises
are closely linked to the nutrition of the
animal which, in turn, is determined by the
amount of feed consumed and the nutritive
value of the diet. The accurate measurement
of dry matter intake and the degree of selec-
tion of specific plant species in mixed
pastures by the grazing animal are vital for
evaluating the energy balance of the animal.
The nutritive value of the feed is deter-
mined by its chemical composition and the
degree to which these chemical substances
are transformed in the gut into nutrients
required by the animal. Fibre digestibility is
determined by the potential extent and rate
of digestion, and rate of passage. Microbial
protein synthesis is the main source of
-
amino nitrogen supply to the ruminant and
is of particular importance for diet formula-
tion of ruminants. The measurement of
digesta volume and flow through the gut or
through segments of the digestive tract pro-
vides information regarding the quantity of
feed components in the gut and the effi-
ciency of their utilization by the animal.
These measurements, used for optimizing

animal production, can all be made rou-

tinely by means of techniques using indi-

gestible marker substances which are

quantified in the faeces or in segments of

the digestive tract, depending on the pur-

pose of the study. This chapter is a critical

evaluation of the more commonly used

markers in animal nutrition.

Properties of Markers

Ideal markers are indigestible substances

not absorbed or affected by the digestive

tract. They should also not affect or be

affected by the microbial population in the

tract. Markers must be closely associated

with or physically similar to the undigested

nutrient in question, or must flow through

the digestive tract at an identical rate and

not separate from the respective labelled

fractions. Attachment of a particle-bound

marker is critical in digestive segments such

as the rumen where particle flow varies, but

adherence becomes less critical post-

ruminally, where variation in particle flow

is small. Furthermore, highly sensitive and

specific analytical methods for quantifying

markers must be available. The sensitivity

© CAB International2000. Farm Animal Metabolism and Nutrition

(ed. J.P.F. D’Mello) 255