997.
Two steers excreting similar quantities of organic matter daily were grazed at pasture during the summer of 1961. The four experiments each involved a preliminary period of five days dosing with Cr
2O
3 to reach a fairly constant excretion. The steers received a daily dose of Cr
2O
3 either in oil suspension or in shredded paper. The carriers and steers were interchanged for each trial. For two of the trials each steer in turn was harnessed every other day and all its dung collected in a bag. Total faecal excretion of organic matter was measured from the bagged steer and estimated from the Cr
2O
3 concentration in a composite sample made up from all dung pats voided during the ten-day collection period. In the other two trials the steers were not harnessed and each dung pat was separately sampled and analysed for Cr
2O
3 in the organic matter. The average recovery of Cr
2O
3 in the first two trials was 99·1 (oil) or 94·4% (paper). Calculating the faecal organic matter excretion from the concentration of Cr
2O
3 in the faeces and the quantity given daily overestimated it by 3·5 to 8·0%. There was no significant difference between shredded paper and oil as carriers of Cr
2O
3 for estimating the quantity of organic matter excreted. There were 37% and 22% less variation between dung pats in Cr
2O
3 concentration when this was administered in shredded paper than when given in oil suspension.
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