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A method of calculating dry matter digestibility of forages from the protein content and predicted protein digestibility is presented. The data obtained are compared with data obtained by conventional and by lignin-ratio methods of determining digestibility. The average digestibilities calculated in the various ways from data of lamb and steer trials are, in general, similar, but the slopes of the regressions of dry matter digestibility on lignin content are generally less when data are obtained by the “protein digestibility” method. This difference in slopes is statistically significant only in the case of the lamb trials. It would appear from the data reported in this paper that the method may be used with a satisfactory degree of accuracy for the determination of digestibility of dry matter by grazing steers. A difference in digestive capacities of cattle and sheep has been demonstrated; sheep are apparently more efficient digesters of protein in low-protein forage than are cattle. The difference disappears above about 15% protein in the dry matter of the forage.
Richard Forbes (Mon,) studied this question.