Evaluation of Radiocerium as a Nonabsorbed Reference Material for Determining Gastrointestinal Sites of Nutrient Absorption and Excretion in Cattle

Abstract

A series of experiments utilizing 38 dairy cattle was conducted to evaluate radiocerium as a nonabsorbed reference material. Dry matter and daily administered Ce144 were measured throughout the gastrointestinal tracts of animals ranging in age from young calves to mature cows. Daily fecal recovery of Ce144 from 11 animals fed grain and hay averaged 97% (CV=19%) of the daily dose after the fourth day. No pattern of diurnal variation in Ce144 excretion was evident in fecal concentrations during successive 2-hr collections for 90 hr from two cows. The first measurable amounts of radiocerium appeared in fecal samples collected 10 hr after single doses to two cows. Maximum excretion occurred between 20 and 40 hr after dosing. Similar results were obtained with simultaneously administered chromic oxide. Within-animal comparisons of Ce144 given by capsule with Ce144 previously mixed in the feed were made for both milk- and grain-fed calves. With grain-fed calves, no differences were detected in gastrointestinal distributions of the two radiocerium isotopes. However, with milk-fed calves, capsules containing Ce144 went to the rumen, whereas milk containing the Ce144 was directed to the abomasum. In the digestive tracts contents of 19 animals over 90% of the radiocerium was adsorbed on to undigested residue, as indicated by ultracentrifugation or availability to cation exchange resin.