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

Substitution effect, %
1,5
1
0,5
0
0 1 2 3 4
Biomass, t/ha
Figure 3 – Influence of ryegrass biomass on the substitution effect of corn grain (from Molle et
al., 1997)
The crude protein content of the supplement could have an important effect on
both herbage selection and intake. A previous study which developed a model to predict herbage
intake in grazing dairy sheep in the Mediterranean environment (Avondo et al., 2002) found that
the quantity of crude protein in the supplement (g/d) was negatively correlated with intake. The
negative correlation between quantity of DM and intake was less pronounced. Moreover, the
effect of the supplement in reducing pasture intake increased as the quantity of crude protein in
the herbage increased. These results seem to suggest that protein requirements may play a role in
the sheep's self-regulation of intake.
Balancing Diets For Grazing Lactating Ewes
Diet balancing for grazing dairy sheep using nutritional indicators
Optimal dietary nutrient concentration for grazing sheep was given by Cannas (2004).
However, due to the uncertainties related to the prediction of the quality or quantity of the sward
ingested by the animals, diets balancing in grazing animals is much more difficult than it is for
confined ones. In some situations it is even impossible to provide properly balanced diets,
especially when pasture is very rich in some specific nutrients (e.g. protein or NDF). In these
cases the goal of a nutritionist should be to supply the least unbalanced diet, not a balanced one.
In all grazing systems, the process of diet balancing (or that of providing the least unbalanced
diet) should be based on the following strategy: the predictions of animal requirements and of
pasture intake and quality should be integrated with the appraisal of nutritional indicators able to
provide information on actual diet composition, rumen and digestive tract function, presence of
metabolic disorders, and level of coverage of the requirements.
The best nutritional indicators so far developed for sheep are yield and quality of the milk,
health status of the animals, some blood components, the concentration of urea in the milk, the
body condition of the animals, and the characteristics of the faeces. Some of these indicators will
be discussed here.
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