An assessment of chromic oxide as an indigestible marker for digestion studies in sheep

SUMMARY Fistulated cross-bred sheep were given, by means of continuous feeders, concentrate diets containing chromic oxide (Cr 2 O 3 ). Dry-matter digestibility coefficients predicted from the faecal concentration of Cr 2 O 3 were compared with those obtained by total collection of faeces, and the concentration of Cr 2 O 3 in spot samples of faeces taken at different times of day was compared with that in faeces bulked over an 8-day collection period. The rate of flow of digesta from the abomasum and the partition of digestion between the stomach and intestines, calculated from the concentration of Cr 2 O 3 in samples of abomasal digesta, were compared with values obtained using two markers, one of which remained in solution while the other was adsorbed by particulate matter. Récovery of Cr 2 O 3 in the faeces ranged from 91 to 101% and predicted dry-matter digestibilities were similar to those obtained by total collection. There was no diurnal variation but there was marked random variation in the concentration of Cr 2 O 3 in spot samples of faeces. Cr 2 O 3 was shown to behave independently of the particulate matter in digesta and, as a single marker, it significantly underestimated the flow of digesta from the abomasum relative to the double marker method. Cr 2 O 3 thus overestimated digestion in the stomach and underestimated digestion in the intestines. It was concluded that Cr 2 O 3 was not a satisfactory marker for studies of the flow of digesta and hence the partition of digestion within the gastro-intestinal tract when digesta samples are taken from a simple cannula.