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Comparisons of the Disappearance of Ytterbium-169, Chromium-51, and Intrinsically Carbon-14-Labeled Plant Cell Walls from Continuously Fed Fermentors^{1, 2,}

Agricultural Research Service, USDA, Beltsville, Maryland 20705
Animal Sciences Department University of Maryland, College Park 20742

ABSTRACT

An experiment was conducted with labeled wheat plant cell walls intrinsically labeled with ¹⁴C and treated with extrinsic markers to measure their rate of disappearance from fermentors fed every hour. The systems were maintained at pH 7.0 in the first trial and at pH 2.5 in the second trial to mimic acidities for the rumen and abomasum. In each trial 12 fermentors were fed hourly .4 or .8 g orchardgrass hay pellets, infused continuously with 500 or 1000 ml of buffered solution daily, and dosed with three marked cell wall treatments. Treatments were 1) ¹⁴C cell walls, 2) ¹⁴C cell walls mordanted with Cr containing tracer ⁵¹Cr, and 3) ¹⁴C cell walls treated with Yb containing tracer ¹⁶⁹Yb. Marker disappearance was faster at pH 7.0 than at pH 2.5. Marker disappearance was faster for the high than the slow liquid infusion rate. Disappearance was also faster for the high feed rate than the low feed rate. Fractional rates of ¹⁴C cell wall disappearance (h^–1) were –.042, –.035, and –.029 in the untreated, Yb-treated, and Cr-treated cell walls, and rates of ¹⁶⁹Yb and ⁵¹Cr disappearance were –.039 and –.025, respectively. Treating ¹⁴C cell walls (internal control) with Cr or Yb reduced disappearance compared to nontreated ¹⁴C cell walls (external control). Differences in rates of marker disappearance and interactions of markers, pH, infusion, and feed rates support the need for caution in interpretation of kinetic data in general and comparison of results obtained with different markers.

¹ Scientific Article Number A-4336.

² Contribution Number 7325 of the Maryland Agricultural Experiment Station.