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

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Abstract
Dry matter and daily administered radiocerium Ce144 were measured throughout the gastrointestinal tracts of dairy cattle ranging in age from young calves to mature cows. Daily fecal recovery of Cel44 from n animals fed grain and hay averaged 97% (CV = 19%) of the daily dose after the 4th day. No pattern of diurnal variation in Ce144 excretion was evident in fecal concentrations during successive 2 hr. collections for 90 hr. from 2 cows. The 1st measurable amounts of radiocerium appeared in fecal samples collected 10 hr. after single doses to 2 cows. Maximum excretion occurred between 20 and 40 hr. after dosing. Similar results were obtained with simultaneously administered chromic oxide. Within-animal comparisons of Ce141 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 2 radiocerium isotopes. However, with milk fed calves, capsules containing Ce141 went to the rumen while milk containing the Ce144 was directed to the abomasum. In the digestive tract contents of 19 animals, over 90% of the radiocerium was adsorbed onto undigested residue as indicated by ultracentrlfugation or availability to cation exchange resin.