Copper is one of the most vital trace elements in ruminant nutrition. It is required for several metabolic activities and it is also an essential component of several physiologically important metalloenzymes. Thus copper deficiency in ruminants results in distinctive pathologies, and hence in significant economic losses to farmers. Copper deficiency results from very low copper in diet (primary copper deficiency) and interference with Cu absorption in the animal due to Mo and S in food or water (secondary copper deficiency). The molybdenum-induced copper deficiency that affects ruminants can be attributed to the formation of thiomolybdates (TMs)from molybdate and sulfide in the rumen. The TMs formed then react irreversibly with copper to form insoluble Cu-TM complex which ultimately end up being excreted, thus reducing copper bioavailability to the ruminant. <p>In this study, an attempt has been made to use computer simulations to model speciation of copper in rumen fluid in the presence of TMs with the aim of understanding the extent to which TMs affects the levels of copper in the rumen. <p>This was done by initially refining the computer model of copper speciation with respect to low molecular mass (LMM) ligands in bovine rumen with the aim of correcting the discrepancy that was observed during experimental validation of the computer model in a previous study. To this end, mass balance equations which describes the distribution of Cu(II) amongst the different ligands were encoded into a spreadsheet to calculate equilibrium concentration of all species. Formation constants obtained from literature as well as those obtained from studies in our group were used as input values in the spreadsheet. Results show that at average ruminal pH, the metal would be present mostly as carbonate and phosphate complexes. The results obtained from the computer model in the present study were validated using 1H NMR experiments on simulated rumen fluid as well as actual rumen fluid containing Cu(II); using acetic acid chemical shift as the probe for monitoring the speciation pattern. Excellent agreement was observed between the computer model and experimental results. Discrepancy was however observed upon introduction of copper lysine as copper source into the model. Incorporation of a mixed ligand complex of Cu(II), acetate and lysine into the computer model gave an excellent agreement between the computer model and experimental results. <p>The study was extended to include glycine, histidine, methionine and EDTA complexes as the copper source in both rumen saliva (McDougalls solution) and rumen fluid. Results show that only the histidine and EDTA complexes persist to any significant extent, in spite of the large number of competing ligands present in these matrices.<p>In this study, success has also been achieved in the integration of the slow (kinetically controlled) formation of TMs and copper-tetrathiomolybdate (TM4) complexation into the previously developed model for the rapidly equilibrating copper-ligand speciation. To simulate the formation of the TMs and Cu-TM4 complex with respect to time, the differential equations representing rate expressions for each chemical species were solved to obtain an analytical solution using the Laplace transform method. The analytical solutions obtained were encoded in a spreadsheet and calculated as function of time to obtain time dependent concentrations of TMs and Cu-TM4 complex. This was then integrated with previously developed model for the rapidly equilibrating copper-ligand speciation in the rumen. The kinetic data used in the simulation of the formation thiomolybdates was obtained fron literature wheras that for Cu-TM4 complexation was obtained from our lab using Cu(II) - Ion Selective Electrode. The results show that that in the presence of TM4 the, Cu(II) bound to low molecular ligands in the rumen is drastically reduced confirming the effect TM4 on Cu(II) observed in several in vitro studies.<p>The study shows that in thiomolybdate contaminated rumen environment, the bioavailability of copper is considerably reduced. Though metal bioavailabilities are hard to predict this approach could help better our understanding of this process.

Copper is one of the most important trace elements in ruminant nutrition. Its deficiency causes certain pathologies that can be cured by supplementation, by either five ("inorganic") or complexed ("chelated") forms. With the objective of being able to quantitatively compare the distribution of copper between the two forms of supplements, the speciation of copper in ruminant fluids was studied here. For this study, copper lysine supplement was used. It was necessary to first study the acid-base and complexation chemistry of lysine with copper (II). In addition, the complexation chemistry of glycine and histidine, were investigated. Mass balance equations were used to describe the distribution of copper (II) amongst different ligands. The results of the distribution of copper (II) ions in McDougall's solution (a simulated form of bovine saliva), indicate no significant differences in the distribution of copper using the different form of supplements. 1H NMR was used to validate the results from the computer model. Using a combination of the results from the saliva simulation model and the chemical shifts from the NMR studies, the chemical shift changes that would accompany the addition of copper (II) to McDougall's solution were predicted. Results from the models do not show any appreciable differences from experimental values. Rumen samples were collected. Important peaks in the 1H NMR spectrum were assigned. The spectrum indicated that acetic acid, resulting from the fermentation in the rumen, was a good probe for monitoring the speciation pattern. Speciation calculation indicated that the bulk of the copper would be bound to ammonia in the rumen. Changes in chemical shifts that result from the introduction of copper (II) to the rumen contents were predicted. Results were compared with experimental values. Agreement between the two sets of results was found to be satisfactory. The study shows that any advantages that result from the use of copper lysine supplement are not as a result of its remaining intact. Though metal bioavailabilities are hard to predict this approach could help better our understanding of this process. The methods developed here could be extended to other metal complexation problems in biological fluids. (Abstract shortened by UMI.)

Copper is one of the most vital trace elements in ruminant nutrition. It is required for several metabolic activities and it is also an essential component of several physiologically important metalloenzymes. Thus copper deficiency in ruminants results in distinctive pathologies, and hence in significant economic losses to farmers. Copper deficiency results from very low copper in diet (primary copper deficiency) and interference with Cu absorption in the animal due to Mo and S in food or water (secondary copper deficiency). The molybdenum-induced copper deficiency that affects ruminants can be attributed to the formation of thiomolybdates (TMs)from molybdate and sulfide in the rumen. The TMs formed then react irreversibly with copper to form insoluble Cu-TM complex which ultimately end up being excreted, thus reducing copper bioavailability to the ruminant. <p>In this study, an attempt has been made to use computer simulations to model speciation of copper in rumen fluid in the presence of TMs with the aim of understanding the extent to which TMs affects the levels of copper in the rumen. <p>This was done by initially refining the computer model of copper speciation with respect to low molecular mass (LMM) ligands in bovine rumen with the aim of correcting the discrepancy that was observed during experimental validation of the computer model in a previous study. To this end, mass balance equations which describes the distribution of Cu(II) amongst the different ligands were encoded into a spreadsheet to calculate equilibrium concentration of all species. Formation constants obtained from literature as well as those obtained from studies in our group were used as input values in the spreadsheet. Results show that at average ruminal pH, the metal would be present mostly as carbonate and phosphate complexes. The results obtained from the computer model in the present study were validated using 1H NMR experiments on simulated rumen fluid as well as actual rumen fluid containing Cu(II); using acetic acid chemical shift as the probe for monitoring the speciation pattern. Excellent agreement was observed between the computer model and experimental results. Discrepancy was however observed upon introduction of copper lysine as copper source into the model. Incorporation of a mixed ligand complex of Cu(II), acetate and lysine into the computer model gave an excellent agreement between the computer model and experimental results. <p>The study was extended to include glycine, histidine, methionine and EDTA complexes as the copper source in both rumen saliva (McDougalls solution) and rumen fluid. Results show that only the histidine and EDTA complexes persist to any significant extent, in spite of the large number of competing ligands present in these matrices.<p>In this study, success has also been achieved in the integration of the slow (kinetically controlled) formation of TMs and copper-tetrathiomolybdate (TM4) complexation into the previously developed model for the rapidly equilibrating copper-ligand speciation. To simulate the formation of the TMs and Cu-TM4 complex with respect to time, the differential equations representing rate expressions for each chemical species were solved to obtain an analytical solution using the Laplace transform method. The analytical solutions obtained were encoded in a spreadsheet and calculated as function of time to obtain time dependent concentrations of TMs and Cu-TM4 complex. This was then integrated with previously developed model for the rapidly equilibrating copper-ligand speciation in the rumen. The kinetic data used in the simulation of the formation thiomolybdates was obtained fron literature wheras that for Cu-TM4 complexation was obtained from our lab using Cu(II) - Ion Selective Electrode. The results show that that in the presence of TM4 the, Cu(II) bound to low molecular ligands in the rumen is drastically reduced confirming the effect TM4 on Cu(II) observed in several in vitro studies.<p>The study shows that in thiomolybdate contaminated rumen environment, the bioavailability of copper is considerably reduced. Though metal bioavailabilities are hard to predict this approach could help better our understanding of this process.