Chelated trace elements are increasingly used to supplement livestock feeds despite little evidence that they have a higher nutritive value than simpler and cheaper inorganic salts. Advantages for chelated sources should be most evident for elements such as copper (Cu) in the diet of ruminants which rarely absorb more than 10% of the Cu they ingest because of antagonisms with sulphur and molybdenum initiated in the rumen.

A copper:lysine complex (CuPLEX, 100; ZinPro Animal Health Ltd) was, therefore, compared with cupric sulphate (CuSO4.5H2O) for ability to increase liver Cu stores in sheep. Five groups of five Suffolk cross sheep, 10 months old and weighing 44kg on average, received 4.0kg DM daily of a basal diet of (kg/l00kg) whole oats (90.8), urea (1.8), calcium sulphate (1.4), sodium bicarbonate (1.8), and potassium chloride (0.5), with trace elements and vitamins A, D and E coated onto the grain in a sugar solution. A control group received the unsupplemented diet containing 3.5mg Cu/kg DM while four groups received Cu:lysine or CUSO4 added at a lower (1) and a higher (2) level, giving diets containing 9.8 and 14.6 or 8.4 and 13.2mg Cu/kg DM, respectively.