Animal‐based methods of determining herbage intake and quality under grazing conditions

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Abstract
The better techniques used to quantify intake of pasture by ruminants require faeces excretion to be quantified. Chromium EDTA is a better marker for this purpose than is Cr2O3 as it can be analysed for more accurately and rapidly. In calculating faeces Excretion constantly infused Cr EDTAor ruthenium tris chloride, a particulate marker, requires less sampling of faeces for similar accuracy than when 12 hourly doses of Cr EDTA or Cr2O3 are administered per rumen. Under conditions where the mean retention time of a marker varies in the gut, faeces bags are the only way of accurately quantifying faeces excretion. After faeces excretion has been quantified, intake can be estimated by measuring digestibility of the ingested herbage in various ways. Suggestions are given when lignin and in vitro digestion are used for this purpose, which may increase the accuracy of intake measurements. The most accurate method of measuring digestibility at present involves using ruminants fitted with oesophageal fistulae and measuring the digestibility of this dried herbage with ruminants in cages. The better the quality of a herbage the greater the rate of ruminant production. However ruminant production can only be measured accurately in the long term. A simple technique that can predict whether gross deficiencies of protein or minerals exist in an ingested herbage is suggested. In addition this technique can indicate whether the rumen capacity and thus intake is not limited by factors such as rapid fermentation of the herbage in the hindgut and can also indicate whether the gut is functioning constantly, when faeces are sampled.

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