Résumé
A study was conducted to determine the copper status of different classes of grazing sheep during two different seasons on a farm located in southern Punjab, Pakistan. A complete free-choice supplement was available to all animals throughout the year. Soil, forage and blood plasma from animals were taken eight times during the year [2005] [four times in both summer and winter seasons]. Soil Cu2+ was affected by the seasonal changes [P<0.001], higher in summer than that in winter and was significantly higher than the need of plants during both seasons. While forage Cu2+ level showed non-significant seasonal [P>0.05] fluctuation in winter. It was adequate for ruminants' requirements during both seasons. plasma Cu[2+] concentrations of all classes of sheep were significantly higher in winter than that in summer showing the seasonal changes [P<0.001]. Higher plasma Cu[2+] was found in male sheep than lactating and non-lactating sheep during both seasons. The low Cu2+ in plasma in lactating sheep may have been due to its secretion in milk. In winter forage Cu[2+] contributed in enhancing the plasma Cu[2+] levels, but in summer the forage Cu[2+] level, although very high, was ineffective in elevating plasma Cu[2+] levels in all classes of sheep. Based primarily on plasma analyses it was concluded that although, the adequate level of plasma Cu[2+] was found, it was on borderline deficient levels. Thus supplementation is needed with mixture containing Cu[2+]. The plus copper should be continuously supplemented to grazing animals in this semiarid region of Pakistan