Herbage utilisation

Under-grazing on the other hand will result in decreased utilisation of herbage by the animal, due to large amounts of senescent and wasted material. When a sward reaches full canopy, the rate of senescence will equal the rate of new leaf appearance and there will be no further increase in the weight of the standing crop (Fig. 2.2). 

The organic farmer must be fully satisfied that close grazing does not result in under-nutrition. It need not, but any system based on utilising herbage as fully as possible tends to make the dairy cows eat second or third choice herbage, which may reduce intake slightly and thus milk yield. 

The use of radioactive magnesium in tracer studies indicates that the magnesium present in food is poorly absorbed from the alimentary canal in some cases only 50 g/kg of the herbage magnesium can be utilised by the ruminant. AVhy this is so in ruminants is not known. Since adult animals have only very small readily available reserves of body magnesium, they are dependent upon a regular dietary supply. 

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