Measurement of protozoa, using phosphatidyl choline, and of bacteria, using nucleic acids, in the duodenal digesta of sheep fed chaffed lucerne hay (Medicago sativaL.) diets

Abstract

SummaryThe use of phosphatidyl choline (PC) as a marker of protozoa in duodenal digesta was examined in sheep fed chaffed lucerne hay (Medicago sativaL.; 330–950 g organic matter/day) either once daily or hourly.PC was present in rumen protozoa (N:PC-P = 185±6·4) but was not detected in rumen bacteria. Dietary intake of PC was less than 5% of the daily passage of PC from the stomach (7·49 mg PC-P/day). A comparison of the SA of PC-P in protozoa and in duodenal digesta of sheep given a continuous intraruminal infusion of32P-orthophosphate showed that the proportion of dietary PC-P in duodenal digesta was negligible.The limitations and validity of PC as a marker of protozoa in duodenal digesta are discussed. The daily passage of protozoal N from the stomach (1·38 ± 0·125 g/day) estimated with PC was not affected by frequency of feeding but protozoal N yield (4·96 ± 0·509 g/kg organic matter apparently digested) declined with increasing feed intake.The SA of DNA-32P, RNA-32P and readily extractable phospholipid-32P (REPL-32P) in rumen protozoa, bacteria and duodenal digesta were similar, showing that the DNA, RNA and REPL-P in duodenal digesta were of microbial origin. A method is described for the estimation of bacterial REPL-P and bacterial N in duodenal digesta using DNA, RNA or DAPA as markers.The calculated total microbial REPL-P (bacterial plus protozoal) in digesta using DNA or RNA as markers was in close agreement with values obtained by direct measurement. It was estimated that protozoa contributed 22 and 14% of microbial REPL-P and microbial N, respectively. Bacterial REPL-P and bacterial N values estimated with DAPA as the marker were higher than values obtained with DNA or RNA. These results are discussed with regard to the use of these markers.