The use of chromium oxide to estimate the faecal output of Merinos

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Abstract
The pattern of chromium oxide (Cr2O3) excretion was studied in Merino wethers. The sheep were dosed twice daily with Cr2O3 at fixed times. In the main series of experiments, sheep were fed fresh herbage in metabolism pens. An oaten chaff diet was also employed. In all cases a diurnal pattern of Cr2O3 excretion in the faeces was observed. The pattern was not consistent from day to day, nor was there any consistent effect of level of intake or feeding frequency on the excretion pattern. Distributions of Cr2O3 were examined in eight grazing sheep killed ½–4 hr after dosing. In six of the animals high concentrations of the marker were found to be mixed with the reticuloruminal ingesta, while low concentrations were observed in the other stomachs. In the remaining two animals high concentrations were observed in the omasum and abomasum, from which it was inferred that the dose had by-passed the main bulk of the reticulorurninal ingesia. It seems unlikely that any real advantage is to be gained by painstaking selection of particular times for dosing and faeces sampling in different environments; and it is suggested that convenient fixed times — say 6 a.m. and 3 p.m., or 9 a.m. and 5 p.m. — should prove satisfactory in estimating output of faeces of grazing animals under a wide range of conditions. In 40 sheep-periods of 10–14 days, the mean daily output of faeces organic matter by pen-fed wethers was estimated with mean 101% and error ±12% of the true figures, by analysis of a single bulked sample obtained by dosing and grab sampling at about 9 a.m. and 5 p.m. daily. In 40 periods when samples were bulked over 5–7 days the average estimate was 102 ± 14% of the true figure. Comparison under extensive grazing conditions showed that estimates obtained by dosing and sampling only once per day were generally some 15% higher than those obtained by dosing and sampling twice daily.