Particulate Rumen Turnover Rate Measurement as Influenced by Density of Passage Marker

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Abstract
Alterations of estimates of ruminal turnover rate by density, alfalfa fiber Cr concentration or sampling site were evaluated. Alfalfa fiber density was raised by mordanting with increasing Cr concentrations. Three Holstein cows were fed for ad libitum intake equal portions of a total mixed diet 3 times a day. After a pulse dose of maker, fecal and ruminal grab samples were collected from cows at scheduled intervals for 5 days. Linear regression analysis was used to measure slopes of declining phase of marker excretion curves. Cell wall densities (g/ml) and ruminal turnover rates (h-1) based on ruminal and fecal sampling sites were: 1.21, 0.0116, 0.0236; 1.33, 0.0525, 0.0306; and 2.08, 0.0392, 0.0485 for alfalfa cell wall with Cr concentrations of 7.01, 38.67 and 56.76 mg/g. Particle density and Cr concentration, but not sampling site, influenced estimates of ruminal tunover rate.