Evaluation of praseodymium as a liquid marker in rumen turnover studies

The acetate complex of praseodymium chelated to EDTA (Pr-EDTA) was evaluated as a marker of the liquid phase turnover in the rumen. Five rumen fistulated Holstein Friesian cows in week 9 of lactation were fed four times a day a total mixed ration at two levels of intake: high (100% of voluntary intake) and low (80% of voluntary intake). Ruminal turnover time was estimated by a continuous dose of Pr-EDTA during 3 consecutive days followed by total rumen emptying, and calculated as the ratio of net rumen contents to intake in a 24 h period. A pulse dose of cobalt chelated to EDTA (Co-EDTA) was used to estimate liquid rumen turnover time calculated from the slope of its excretion curve, and was considered the control. Praseodymium turnover time was not affected by level of intake (P > 0.05). Compared with Co-EDTA, turnover time values were different (10.8 h vs. 14.7 h, respectively; P < 0.05), which indicates that Pr underestimated liquid turnover time probably as a result of poor distribution within the rumen liquid phase.