Use of Chromic Oxide as an Indicator of Fecal Output for the Purpose of Determining the Intake of Pasture Herbage by Grazing Cows

Summary A series of five trials was conducted to determine the adequacy of Cr 2 O 3 as an indicator of fecal output by grazing cows. Seventeen individual cows were employed in these studies. The Cr 2 O 3 concentration of feces taken reetally at 6 a.m. and 4 p.m. on seven consecutive days and bulked on an equal weight basis provided accurate estimates of the total fecal output. The mean rate of recovery of the ingested Cr 2 O 3 from the combined feces sampled at 6 a.m. and 4 p.m. was 100.58 ± 0.87%. A study of the Cr 2 O 3 concentration-time excretion patterns of grazing cows revealed that from 65 to 141% as much Cr 2 O 3 is voided in the feces at various hours of the day as is found in well-mixed feces representing the total amount of feces voided during a 7-day period. This precludes the indiscriminate adoption of times for the sampling of feces for the purpose of measuring the total output of feees by grazing cows. No difference in the accuracy of the estimated output of feces was found between the administration of Cr 2 O 3 , in capsules and that in concentrate feeds. Also, the effectiveness of the procedure for measuring fecal output was the same regardless of whether Cr 2 O 3 was administered at 6 a.m. or 4 p.m. or at 6 a.m. and 4 p.m. It is suggested that the time and mode of administration of Cr 2 O 3 employed in the conduct of grazing studies should be determined by the nature of the experiment and the convenience of the operation.