Technical note: Validation of energy dispersive X-ray fluorescence for determination of indigestible markers in ruminant fecal and rumen fluid samples.

Abstract

Determination of digestibility and passage rate is important for further understanding of nutrient utilization and thereby aids in improving nutrient utilization efficiency. Titanium dioxide and chromium ethylenediaminetetraacetic acid are commonly used as indigestible markers for determining passage rates of diets to aid in determination of digestibility. Analyzing Ti and Cr involves the use of procedures such as acid digestions, inductively coupled plasma spectroscopy, and atomic absorption. These commonly used methodologies involve hazardous chemicals, destruction of samples, and low sample throughput. The objective of this experiment was to develop and validate an accurate and precise method for measuring both Ti and Cr using energy dispersive X-ray fluorescence (ED-XRF). Energy dispersive X-ray fluorescence is an analytical technique used for analyzing elements in various sample types. The samples were added to the ED-XRF machine and irradiated with X-rays. The intensity of the X-rays emitted (termed fluorescent X-rays) was used for calculation of the concentration of the element. The method for Ti was constructed using fecal samples from cattle consuming three different diet types (finishing diet, dairy lactation diet, and grazing native range pasture). The Cr method was developed for rumen fluid analysis. We compared the machine-calculated concentrations of each element to the concentration calculated by a standard curve. For both the Ti and Cr, the standard curve-calculated value had a lower percent difference overall at 4.56% and 12.59%, respectively, compared to the machine percent difference of 8.35% and 16.38% for Ti and Cr, respectively. To determine accuracy and precision of the method, samples were spiked with various amounts of Ti or Cr and measured for their respective compounds with percent recovery and inter- and intra-assay CV-calculated thereafter. The average recovery for Ti across all diet types was 100.3%, and the recovery for Cr in rumen fluid was 95.7%. The average inter- and intra-assay CV for Ti, across all diet types, were 9.70% and 2.16%, respectively. For Cr, the average inter- and intra-assay CV were 5.42% and 8.45%, respectively. The ED-XRF method requires minimal additional chemicals, is cost-effective, and allows for sample preservation as well as a high throughput of samples. Our results indicate utilization of ED-XRF is an accurate and precise method for determination of Ti in feces and Cr in rumen fluid.