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Dysprosium as an Indicator in Cattle Digestion Trials^{1 ,2,}

University of Arizona, Tucson 85721

Abstract

Two digestion trials were conducted to determine recovery of dysprosium (Dy) from steers and the reliability of Dy as an inert indicator. In trial 1, six steers were fed alfalfa hay sprayed with Dy solution to give a final concentration of approximately 40 ppm elemental dysprosium. Triplicate subsamples of hay and fecal composite (10-day) samples for each steer had mean coefficients of variation of 5.4 and 1.6%, respectively. Mean fecal Dy recovery was 91.3 ± 1.4%. In trial 2, six steers were fed sprayed hay containing approximately 40 ppm Dy, and another six steers were fed unsprayed hay and received approximately 150 mg Dy in each of two boluses/day administered at feeding time. Fecal Dy recovery means were 90.6 ± .2% and 80.4 ± .3% for bolus and sprayed hay treatments, respectively. The low variation within treatments in indicator recovery suggests an unidentified procedural error confounded with treatment, since method of adminstration does not appear to be a feasible cause for the significant treatment effect. Grab sample data indicated a minimum of 2 days should be allowed following introduction of the indicator before total fecal collections are initiated to permit equilibration of the indicator throughout the digestive tract. Concentration of Dy in grab samples collected at 1600 hr were more representative of total collection sample values than were those for samples obtained at 0700 hr or the two combined grab samples. Coefficients of variation for indicator recovery within steers and within days for grab and total collection samples were similar in order of magnitude (8%). Bolus administration of Dy increased the difference in recovery between grab periods (diurnal variation) with only a slight increase in statistical variation. Grab sampling twice daily using Dy as an indicator provided a reliable alternative to total fecal collections in this study. Use of Dy as an indicator in digestion studies is recommended based upon consistent recovery with minimal variation and the availability of a reliable analysis procedure.

¹ Arizona Agricultural Experiment Station Technical Paper 2573.

² This paper is part of a dissertation prepared by the senior author in partial fulfillment for the Ph.D. degree in Agricultural Biochemistry and Nutrition.

³ Department of Animal Sciences.

⁴ School of Renewable Natural Resources.

⁵ Department of Nuclear Engineering.