Chromic oxide (Cr2O3) in paper pellets was used as an indicator for digestibility studies with four Holstein-Friesian cows fed rations composed of different roughage to concentrate ratios. Cows A and B received one pellet, or 3.46 g of Cr2O3, whereas cows C and D received three pellets, or 10.38 g of Cr2O3, daily.Recovery of Cr2O3 in the feces varied from 84 to 103% for animals A and B and from 92 to 95% for animals C and D. The coefficients of apparent digestion of dry matter were lower (P < 0.01) when the Cr2O3 method was used instead of the conventional method. When samples were taken at 0500, 0900, 1300 and 1700 hours, the Cr2O3 method gave average estimates of digestibility for animal pairs A, B and C, D that were 94.2 and 97.5% of those obtained by the conventional method. Standard deviations for both the Cr2O3 and conventional methods were relatively high.Excretion patterns of Cr2O3 were not signicantly correlated with those of crude protein, phosphorus and calcium. The average concentrations of crude protein, phosphorus and calcium in compounded feces samples collected at 0500, 0900, 1300 and 1700 hours were 101.3, 100.6 and 96.7% of those in samples of the total excretions.The daily administration of 10.38 g of Cr2O3 at 0900 hours for eight days, and the collection of fecal grab samples at 0500, 0900, 1300 and 1700 hours daily during the last five days seemed satisfactory for estimating apparent digestibility of dry matter.
Effect of forage source and a supplementary methionine hydroxy analog on nitrogen balance in lactating dairy cows offered a low crude protein diet
