An Evaluation of the Chromic Oxide Method for Determining Digestibility

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Abstract
Eight lactating dairy cows were used in a ten-day digestion trial, in which the conventional total collection method of determining digestibility was compared with the grab-sampling technique using chromic oxide as an indicator. Variations in the excretion of chromic oxide and crude fiber at 2-hour intervals over a 24-hour period were studied. Statistical analysis showed no significant differences between the 2 methods of determining the digestibility of the rations. Analyses of samples from the total fecal composites for the first 6 days of the ten-day trial revealed coefficients of digestibility comparable to those obtained for the entire period. Considerable variations were found in chromic oxide content of the feces samples taken at various hours of the day, regardless of whether chromic oxide was administered once or twice daily. These variations make it difficult to select a sampling period which will give approximately 100% recovery for all cows for a given day; however, these data indicated this can be overcome in digestion studies by sampling the feces for a ten-day period. Hourly variations in chromic oxide excretion were not associated with excretion of crude fiber.