A comparison of two non-radioactive digesta marker systems for the measurement of nutrient flow at the proximal duodenum of calves

SUMMARY The use of non-radioactive ruthenium phenanthroline (Ru-P) and chromium EDTA (Cr-EDTA) as dual phase markers of digesta flow was examined and compared with chromium sesquioxide (Cr 2 O 3 ) in conjunction with spot samples of digesta collected from T-shaped cannulae situated in the proximal duodenum of weaned calves. In vitro estimates of organic matter digestibility indicated that on a cubed barley diet, Ru-P exhibited toxic effects at concentrations on 2·2 × 10 –5 M and above. No such effects were noted with Cr-EDTA. Subsequently satisfactory infusion rates of 12 mg Ru and 280 mg Cr/kg dry-matter intake were established. Daily flows of organic matter, starch, nitrogen, fibre, sodium and potassium at the proximal duodenum were calculated by the dual phase marker system and by Cr 2 O 3 , and regression equations relating these two for each dietary component were calculated. Examination of the intercepts revealed that they all differed significantly from zero ( P < 0·05) whilst all the regression coefficients were significantly different from unity ( P < 0·05), thus indicating that Cr 2 O 3 underestimated nutrient flows at low flow rates and overestimated them at high flow rates relative to the corresponding estimates based on Ru-P plus Cr-EDTA.