Uso de espectrofotometría de absorción atómica para cuantificar la liberación ruminal in vitro de selenio a partir de alfalfa (Medicago sativa L.)

Abstract

El selenio (Se) es un oligoelemento esencial en rumiantes. Siendo relativamente nuevo el interés de su influencia en la fisiología animal, el objetivo de este trabajo fue caracterizar la liberación in vitro de Se desde alfalfa en fluido ruminal. Así, fue necesario poner a punto las determinaciones para cuantificar Se, en forraje y en fluido ruminal. Los resultados de la verificación de la performance para la determinación de Se en forrajes y fluido ruminal, indican que ambas técnicas son aptas para el uso en los fines requeridos. Por el lado de la liberación, se concluyó que la liberación de Se desde alfalfa es paulatina en el tiempo y que la variación en las primeras 5 horas podría vincularse al intercambio que los microbios ruminales realizan con el medio.

Selenium is a trace element declared essential since 1973 and may be deficient in soils, plants and ruminants in several regions of Argentina, including Buenos Aires province. The main disadvantage for its assimilation in ruminants is due to the metabolism of ruminal microorganisms, which reduce selenium to its insoluble form. Being relatively new its physiological interest, there are few investigations regarding its ruminal metabolism. Therefore, the objective of this work was to characterize the release of selenium in alfalfa incubations under in vitro conditions. Thus, it was necessary to set up the determinations of selenium, in forage and ruminal fluid, through a hydride platform coupled to an atomic absorption spectrophotometer. For the methodological verification, the parameters analyzed were: limit of detection, range of work, bias, precision by repeatability and intermediate precision, recovery and expanded relative uncertainty, following the guidelines of the Association of Official Analytical Chemists. Regarding the ruminal release of selenium, two different treatments were evaluated in vitro: with ruminal fluid (T1) and without ruminal fluid (T2). The results on the verification of methodological performance for the determination of selenium in forages and ruminal fluid, indicate that both techniques are suitable for the required purposes. The in vitro ruminal release presented heterogeneous variance according to treatment, showing greater variability in T1. The in vitro release of Se from alfalfa reached its maximum at hours 1 and 2 after the beginning of the trial, and then it descended until the hour 5, after which it remained relatively stable. When analyzing descriptively the residue of alfalfa from the incubations of the treatments, the highest final concentration of Se was found in the treatment T1, so it is inferred that the ruminal microorganisms could be assimilated it and fixed it to the remaining non-digestible fibers. It was concluded that the release of Se from alfalfa is gradual over time and that the variation in the first 5 hours could be linked to the exchange that ruminal microbes made with the medium.