Copper
Copper is an essential trace element required for enzyme systems, iron metabolism, connective tissue metabolism, integrity of the central nervous and immune systems. Copper functions in the immune system through energy production, neutrophil activity and antioxidant enzyme production. It also aids development of antibodies and lymphocyte replication. As a regulator of Cu- superoxide dismutase, it aids in removal of free radicals formed during metabolism. Reproductive efficiency may be reduced when a Cu deficiency occurs because of metabolic alterations of enzyme systems. Requirements for copper can vary from 4 to 15 mg/kg depending largely on the concentration of dietary molybdenum and sulphur. The recommended concentration of copper is 10 mg Cu/kg diet. This amount provides adequate copper if the diet does not exceed 0.25 % sulphur and 2 mg Mo/kg diet. Less than 10 mg Cu/kg diet may meet requirements of feedlot cattle as copper are more available in concentrate diets than in forage diets. Copper requirements are greatly increased by both molybdenum and sulphur. The antagonistic action of molybdenum on copper metabolism is greater when the ration is also high in sulphur. Copper is believed to react with thiomolybdates in the rumen to form poorly absorbed insoluble complexes. Thiomolybdates can result in copper becoming tightly bound to plasma albumin and unavailable for biochemical functions and may directly inhibit certain copper-dependent enzymes.
Sulphur reduces copper absorption, perhaps via formation of copper sulfide in the rumen. High concentrations of iron and zinc also reduce copper status, which may increase copper requirements. Absorbed copper is excreted primarily via the bile with small amounts lost in the urine. Considerable storage of copper occurs in the liver. Copper of plant source feedstuffs is 50% as available as that in animal source feeds. Copper sulphate and cupric carbonate are well absorbed. Cupric oxide and sulfide are poorly absorbed by all the species.