A Comparison of the Lignin Ratio Technique and the Chromogen Method of Determining Digestibility and Forage Consumption of Desert Range Plants by Sheep

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Abstract
During the winter grazing season of 1950–51 a study was conducted on desert ranges in northwestern Utah to compare two methods of determining forage consumption and digestibility of native forage species by the use of tracer or indicator plant substances. The one method uses lignin as the indicator substance and is known as the lignin ratio technique. The other method involves plant pigments as the indicator substance and has been termed the chromogen method. Wether sheep equipped with specially constructed fecal bags were allowed to graze temporary enclosures on native forage types composed of single species. Forage samples were taken by careful observation of grazing animals and hand plucking forage comparable to material actually being consumed. The ratio of the various constituents to either lignin or chromogen material in the forage and feces was the basis for determining digestibility. It was found that both lignin and chromogen content could be determined chemically with equal accuracy. However, the coefficient of variation for digestibility among animals was much smaller by lignin determinations than by chromogen determinations. Forage consumption as determined by the lignin ratio technique agreed rather closely with calculated dry matter intake commonly accepted for the various sizes of sheep. Calculated digestibility of dry matter by the use of lignin as the indicator substance compared favorably with digestibility results obtained by other investigators on similar forages. This was not generally true for determinations made by the chromogen method. It was concluded that the chromogen method was not suited for determining digestibility of winter range forage since, in some cases, there was considerably less chromogen material recovered in the feces than was actually consumed. Copyright © . .