Use of 141Ce as a particulate digesta flow tracer in ruminants. I. Determination of uptake on feed and behavior in rumen digesta in vivo

The suitability of 141Ce as a particulate digesta flow tracer is studied in sheep. The amount and the factors of cerium uptake on feed particles by incubating alfalfa hay and sorghum seeds in water containing 141Ce in solution are determined. After soaking one hour, 80% radioactivity is retained on the hay 17% on the sorghum. Incubation time is the main factor determining uptake rate. This uptake is solid on the hay and more fragile on the sorghum. The evolution of 141Ce distribution among the different physical constituents of rumen digesta is studied on two sheep given a single radioactive meal (10μCi). These sheep are fitted with a rumen cannula and fed twice daily with hay (80%) and sorghum (20%). There is little 141Ce in solution in the supernatant liquid after centrifugation of digesta. At the end of the 'labelled' meal, specific radioactivity (RAS) of liquid-phase digesta, separated by filtering on two layers of gauze, is equal to or higher than the RAS of the solid phase. It increases up to the next unlabelled meal and then decreases. Microorganisms may cause this transfer of liquid-phase radioactivity to the large particles. Specific radioactivity of the microorganisms remains very high after the 'labelled' meal as compared to that of different granulometric fractions of solid digesta