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Some Factors Influencing Estimates of Digesta Turnover Rate Using Markers¹

US Department of Agriculture, El Reno, OK 73036 and and Oklahoma State University, Stillwater 74078

Abstract

A series of experiments was conducted to evaluate the effects of ytterbium (Yb) and chromium (Cr) as particulate markers and of feeding frequency on particulate turnover estimates. Ytterbium was removed from hay by neutral detergent solution that contained disodium ethylenediaminetetraacetic acid (EDTA) but remained with the fiber fraction if the EDTA was omitted. At 625 µg Yb/g or less, presence of Yb had no effect on in vitro dry matter (DM) or fiber digestibility. When hay was soaked in aqueous solutions of Yb to supply 5 to 40 mg/g hay dry matter, NDF digestibility was decreased 38%»mg Yb^-1 .g hay^-1, even though the maximum amount attached was only 3.5 mg/g hay. Dry matter intake, digestibility and rumen liquid dilution, measured by cobalt-EDTA, was not influenced by feeding frequency. Turnover rate of rumen DM was influenced by a significant interaction between feeding frequency and marker. Similar turnover rates were observed with Yb and Cr when steers were fed twice daily (2.8 and 2.6 %/h), respectively, but rates were different (P<.05) when steers were continuously fed (Yb=2.0; Cr=1.5 %/h). Turnover in the rumen" calculated from samples of neutral detergent fiber obtained from the rumen or from samples of fecal dry matter differed in magnitude, ranking among treatments and in variability from diat calculated from rumen dry matter. Turnover rate calculated from rumen dry matter was correlated (.7 for Yb, .4 for Cr) with DM intake. Correlation of DM intake and turnover from fecal excretion was highly variable depending on the model used.

¹ This research was conducted by the USDA, ARS, Southern Region in cooperation with Oklahoma State Univ. Journal Article 4201 of Agr. Exp. Sta., Oklahoma State Univ., Stillwater 74078.

² USDA, ARS, Southwestern Livestock and Forage Research Station, Box 1199, El Reno, OK 73036.

³ Fisher Scientific Co., 900 Stewart Ave., Piano, TX 75074.

⁴ Dept. of Anim. Sci., Oklahoma State Univ., Stillwater 74074.