X-ray absorption spectroscopy of copper and iron in sheep digesta

The bioavailable supply of copper to ruminants has long been problematic. Complexities in supply exist due to interactions with other dietary elements in the rumen, most notably with iron or molybdenum in combination with sulphur, which can result in copper binding preventing its absorption. The molybdenum-sulphur-copper interaction has been extensively studied over the years. However, very little is known about the iron-sulphur-copper interaction, especially its mode of action in the gastrointestinal tract.

In the present work digesta from the rumen and jejunum of sheep fed a high copper, sulphur and iron diet was analysed using X-ray absorption spectroscopy (XAS).

X-ray absorption fine structure (XAFS) and X-ray absorption near edge structure (XANES) indicated that all of the copper and iron had changed in bonding in the rumen and that the oxidation state of the elements had been reduced into a mix of Fe²⁺ & Fe³⁺ and Cu⁺ with some Cu⁰.

The copper compounds were most likely to be thiol co-ordinated in line with Cu⁺ chemistry. Changes to the copper compounds took place in the jejunum, although thiols were still highly favoured the possible existence of a copper-iron-sulphur complex which also included oxygen and chloride was also observed. This possibly has some resemblance to the crystal structure of bornite.