A Procedure for Measuring the Digestibility of Pasture Forage under Grazing Conditions

The relationship between the chromogen-dry matter ratio of feces voided and that of forage actually consumed was established mathematically as a result of a study of 18 pasture forage mixtures ranging in dry matter digestibility from 51.6 to 74.0%. This relationship allowed the circumvention of the manual sampling of forage, as it was found that the chromogen concentration of the forage could be predicted from a knowledge of the fecal chromogen level. Data on the concentration of chromogen so estimated in the ingested forage may then be employed together with those on the chromogen concentration in the feces in the usual ratio technique for determining the digestibility of consumed forage under conditions of grazing. An alternate procedure for the direct computation of digestibility from the chromogen concentration of the feces was also suggested. When the amount of dry matter voided in the feces per unit of time is known, the dry matter intake of grazing animals may be readily computed from a knowledge of the chromogen level of the consumed forage and of the feces, or from a knowledge of the degree of indigestibility of the forage. Other applications of the principles of this method of measuring pasture forage digestibility and intake are considered.