Nutrition of the grazing ruminant
J.L. Black
CSIRO, Division of Animal Production, Prospect, P.O. Box 239,
Blacktown Australia
Proceedings of the New Zealand Society of Animal Production. 1990,
50: 7-27
Ruminants grazing pasture rarely approach their genetic potential
for meat, milk or wool production. There are wide differences also
between plant species and between leaf, stem and inflorescence fractions
in their capacity to sustain animal production. The relatively low
productivity of grazing ruminants and the differences between plant
components in nutritional value can be explained from an understanding
of the factors that determine nutrient supply to the animal's tissue and
the efficiency of metabolism. Nutrient supply to the tissues depends on
Ii) the nutrient contents of the forage available, which varies between
plant species, their component parts, their stage of maturity and the
growing conditions; (ii) the pasture components actually selected by the
animal which are influenced by ease of eating, taste, odour and tactile
characteristics of the plant material available, its water content, the
structure of the sward, the dimensions of the animal's incisor arcade
and its previous experience; (iii) the amount of each selected component
eaten, which is influenced by the potential of the animal to utilize
nutrients, the capacity of the reticulo-rumen and factors that affect
the rate of digestion and outflow of organic matter from the rumen, and
the time spent in eating and ruminating activities; (iv) modifications
of consumed nutrients by rumen microbes, particularly the extent of
breakdown of plant protein and the relative proportions of volatile
fatty acids produced; (v) the efficiency of biochemical reactions
metabolising the absorbed nutrients. Although a great deal is known
about the way each of these factors influence nutrient supply to grazing
animals, the complexity of the interactions between them often makes it
extremely difficult to identify the specific reasons for reduced
performance in any particular situation. However, by integrating
current concepts and knowledge using computer simulation techniques, the
factors limiting nutrients supply to the animal's tissues can be
determined and the value of alternative management strategies for
improving animal productivity assessed.
Keywords: NZSAPAB;
Grazing ruminant; pasture composition; diet selection; feed intake;
rumen function; nutrient metabolism; computer simulation
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Last Updated 25-01-1997
