Great Lakes Dairy Sheep Symposium - the Department of Animal ...

tendency is more marked the higher the number of botanical species in the pasture, on condition
that botanical heterogeneity is accompanied by a corresponding spatial differentiation of the
various essences. In fact, structural differentiation of pasture facilitates identification and
prehension of the most appetising essences or parts of the plant.
Species which are erect in their growth, such as most forage grasses, offer a better chance
of the sheep selecting morphological parts of the single plant than do creeping species, such as
some spontaneous or cultivated legumes (Table 7) (Avondo and Lutri, 2004).
Table 7 – Protein and digestible organic matter content of the whole plant and of selected
parts of various pasture essences (Avondo and Lutri, 2004).
Digestible organic
Crude Protein
matter
% DM
% DM
Whole Selected Whole Selected
Botanical essence
Grasses
Growth habit Plant part plant part
Barley
Erect 18.2 25.4 68.1 72.0
Bromus spp
Erect 15.8 23.7 69.1 73.7
Mixed pasture Erect 10.1 16.8 62.6 69.8
Mixed pasture Erect 8.8 11.3 73.4 76.6
Mixed pasture
Legumes
Erect 10.8 16.7 - -
Vetch
Creeping 20.9 22.2 66.4 69.1
Clover
Creeping 21.4 26.5 75.1 75.6
Mixed pasture Creeping 16.4 18.0 68.4 68.2
Mixed pasture Creeping 16.8 20.7 - -
In general, as biomass increases so does intake capacity. However, even with high herbage
availability, as pasture quality gets worse, due to the biological evolution toward maturity,
searching for less lignified plant parts or essences results in a reduction in time spent eating.
If biomass levels are high and the grass is over 30 cm high, then sheep may trample the
grass to reach the tips. As a result some of the biomass is wasted and the sheep spend less time
grazing. If, however, the biomass levels are high but the pasture is short and dense, then intake
increases because bite prehension is facilitated. Ideally, in order to avoid the negative effects of
excessive selective activity by the sheep, the pasture should be dense and not more than 8 -10 cm
in height. This can be done by choosing the right type of pasture and maintaining an adequate
stocking rate.
Herbage quality can be expressed in terms of digestibility, filling value, crude protein (CP)
or structural carbohydrate content. It affects pasture intake. Good quality herbage can enable the
"potential" intake to be reached. This is an intake that allows the animal to satisfy its requirements
without physical limitations. Generally the levels of intake observed in highly digestible pastures
are higher than in lignified pastures. It is also true that if the pasture is highly digestible then the
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