Abstract:
The efficacy of 3 copper (Cu) supplements in maintaining adequate Cu status in Shorthorn heifers and Merino wethers was investigated in 3 experiments on alkaline peat soils in the South East of South Australia. The Cu supplements used were: soluble glass pellets containing Cu; copper oxide particles (CuO); Cu as a subcutaneous injection. Pasture contained moderate to high concentrations of molybdenum (Mo) (2.9-12.3 mg/kg), moderate Cu (3.8-8.7 mg/kg) and adequate sulfur (>1.7 g/kg) to limit the absorption of dietary Cu in ruminants. Shorthom heifers with normal Cu status were given 1 of 6 treatments (no Cu; 2 glass pellets; CuO at 3 doses; Cu injection) and introduced to the pasture (experiment 1). There was no liveweight response to any supplement. Relative to untreated heifers, mean liver Cu concentrations were raised only in heifers receiving the glass pellets or the highest dosage of CuO (20 g). The glass pellets maintained an adequate mean liver Cu concentration for at least 44 weeks but the CuO was effective for less than 24 weeks. Hypocupraemic heifers given 1 of 3 treatments (2 glass pellets; CuO; Cu injection) were significantly heavier (P<0.05) than the untreated heifers after 30 weeks (experiment 2). Mean plasma Cu concentrations were adequate at 30 weeks in the glass pellet and CuO groups, but mean liver concentrations indicated severe deficiency in all groups at 30 weeks. There was considerable individual variability in response to the glass pellet and CuO particle treatments, possibly due to the partial regurgitation of some of these orally dosed supplements. Merino wethers with adequate plasma and liver Cu concentrations received 1 of 5 treatments (no Cu; 1 glass pellet; 2 glass pellets; CuO; Cu injection) and were then grazed on a peat soil for a period of 1 year. Plasma Cu concentrations in the control group only indicated hypocupraemia at week 42. Liver Cu concentrations were higher (P<0.001) in all supplemented groups from week 18 to after week 30. Under the conditions of the experiments, 20 g CuO (the suggested dose) for the glass pellets or a single Cu injection were not sufficient to maintain the Cu status of heifers for 1 year. Repeat treatments or higher dose rates were required. The recommended dose rates of the supplements were adequate for wethers.