Methods of administering ytterbium for estimation of fecal output

Abstract

Three experiments were conducted with grazing and penned animals to evaluate the accuracy and precision of different methods of administering ytterbium (Yb) as a marker to estimate fecal output. A paired t test was used to evaluate differences between marker estimates of fecal output and fecal output measured by total collection. Marker administration methods within an experiment were compared in a one-way analysis of variance using the absolute percentage deviation of the marker estimates from total collection. In Experiment 1, wethers were confined in metabolism crates and orally administered either a pulse dose or a once daily dose. Both methods overestimated fecal output (7.3% for the once daily and 11.2% for the pulse dose method); however, the once daily dose was more precise (SE = .78%) than the pulse dose (SE = 2.17%). In Experiment 2, a crossover design with steers grazing dormant bromegrass pasture was employed to compare estimates of fecal output by pulse dosing and once daily dosing of Yb via rumen cannula. Although both methods underestimated fecal output (4.0% for the once daily and 11.5% for the pulse dose), once daily dosing was more precise (SE = 2.36%) than pulse dosing (SE = 3.64%). In Experiment 3, an intraruminal constant release Yb bolus was compared with daily feeding of Yb-labeled supplement using grazing and pen fed steers. The constant release bolus overestimated fecal output 13.8% on pasture and 41.3% in the pen study. Standard errors for the constant release bolus were 4.02% (pasture) and 4.76% (pen). Although use of Yb in a labeled supplement did not provide an accurate estimate of fecal output (80.1 and 106.0% of total collection on pasture and in pen, respectively), it had a lower SE than the constant release bolus method during both the pasture and pen studies. Once daily dosing was more precise than a pulse dose for estimating fecal output in Experiments 1 and 2. The constant release bolus used in Experiment 3 does not appear to be suitable for estimating fecal output of grazing cattle.