|Hall, Mary Beth|
|VAN SOEST, PETER - Cornell University - New York|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2019
Publication Date: N/A
Interpretive Summary: Liquid markers are used in dairy cattle nutrition research to measure how quickly liquid and nutrients pass or disappear from the rumen. The markers must be inert so that they do not create other changes in the digesta. Two commonly used liquid markers -- CrEDTA and CoEDTA -- were tested to evaluate whether they were inert in rumen fluid. Approximately 4% of CoEDTA and up to 14% of the CrEDTA dissociated, opening the possibility that they could have effects other than as markers. This work suggests that other alternative markers be used for nutritional research studies.
Technical Abstract: An ideal digesta marker for use in feeding studies is inert, unabsorbable, and moves with the portion of the digesta it is intended to mark. Both chromium (III) and cobalt (III) salts of ethylenediaminetetraacetic acid (EDTA; CrEDTA and CoEDTA, respectively) have been used as digesta liquid markers in studies with dairy cattle. Although a small portion of these markers are known to be absorbed and excreted in urine, the markers are assumed to remain intact in the digesta. The degree to which these salts remain complexed in solution can be determined through spectrophotometric measurement at the peak absorbance of these colored compounds. The objective of this study was to evaluate whether CrEDTA and CoEDTA dissociate during incubation in rumen fluid. In a complete block design with separate replicated analytical runs, approximately 40 mg/L of Cr from CrEDTA or Co from CoEDTA were incubated in 2 separate preparations of autoclaved clarified rumen fluid (ACRF) from 2 lactating Holstein cows, in water (CrEDTA), or in MES buffer (CoEDTA), as were appropriate reagent blanks. Solution pH were approximately 6.0. Samples were incubated for 24 h at 39C with absorbance measurements recorded at 0, 1, 2, 4, 6, 22, and 24. CrEDTA was measured at 541 nm, CoEDTA at 535 nm, and both were measured with wavescans of 330 to 700 nm. Both CrEDTA in water and CoEDTA in MES maintained absorbance throughout the incubation. In ACRF relative to water, CrEDTA absorbance decreased by 8% at 0 h, and up to a 14% by 24 h. CoEDTA in ACRF showed a gradual decline over time, with an approximate 4% loss in absorbance by 24 h. Responses differed by ACRF prep. Both markers in ACRF showed erratic increases and decreases in absorbance at 330 and 380 nm, though the changes were more marked for CrEDTA; markers not in ACRF showed no response at these wavelengths. Changes in the absorbance values at 330 and 380 nm suggest that soluble phenolic compounds may be involved in the exchange of metals with EDTA, but that does not preclude involvement of other soluble species in rumen fluid. Both CrEDTA and CoEDTA incubated in ACRF showed declines in absorbance at their maximum absorption wavelength suggesting that the metals dissociated from EDTA. The decline was greater for CrEDTA than for CoEDTA.