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Use of Indicators in the Measurement of the Dry Matter Intake of Grazing Animals¹

Two Figures

Cornell University, Ithaca, New York

The adequacy of indicators for measurement of the dry matter intake was examined in a series of trials in which all herbages studied were grazed by and hand-fed to steers. Intake estimates derived from the measurement of indigestibility by the fecal-chromogen method and of fecal outgo by the use of Cr₂O₃ were similar to the measured intakes when feces representative of those voided during periods of 4 or more days were employed.

As a result of an experiment in which a detailed "grab" fecal sampling plan was employed, it was found that the Cr₂O₃ content of the feces voided at intervals of the day is extremely variable. This precludes a random sampling of feces for the purpose of estimating intake. However, the nature of the Cr₂O₃ excretion pattern with respect to time of day indicated that accurate intake estimates could be derived from samples of feces taken at any time provided that the rate of recovery of Cr₂O₃ is known. Consequently, the adequacy of feces obtained at convenient sampling times was examined. Feces samples procured at 6:00 A.M. and 4:00 P.M. and compounded on an equal wet-weight basis during 7 or more days resulted in reliable estimates of dry matter intake.

Although the general applicability of this sampling procedure to a wide variety of grazing conditions remains to be determined, excellent results have been obtained in subsequent experiments in which conditions different from those of the present experiments were imposed. It is indicated that factors which influence the rate of Cr₂O₃ recovery from the feces taken in the morning may effect a change in the recovery of Cr₂O₃ of similar magnitude, though of opposite direction, in the feces taken during the afternoon. The mean rates of recovery of Cr₂O₃ from the feces taken from grazing steers at 6:00 A.M. and 4:00 P.M. were 71.8 and 129.3%, respectively. Wet-bulking of the feces samples taken at these two times of day resulted in an average recovery of 99.95% of the Cr₂O₃ ingested by grazing steers.

² Present address: Virginia Experiment Station, Blacksburg.

Manuscript received 8 June 1953.