Revegetation and sustainable cattle grazing are major objectives in the reclamation of mine tailings at the Highland Valley Copper mine in British Columbia, Canada. A total of 150 cows with their calves grazed forage extremely high in molybdenum (Mo) for 5–6 weeks in the summer and fall for 3 consecutive years (2002–2004). The average stocking rate was 0.89 ha per animal unit month. The animals' diet consisted primarily of alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) containing 100–400 ppm Mo. Each year, the herd was divided into 2 groups of approximately 25 cow–calf pairs. One group was supplemented with 2.5% copper sulphate (CuSO4·5H2O) in loose salt, and the other group was only given loose salt. Clinical signs of Mo toxicity, including lameness, diarrhea, and a faded hair coat, were significantly reduced in the supplement cows compared to control cows, which demonstrated the efficacy of the copper supplement treatment. Cattle also developed a tolerance to grazing high-Mo forage, as lameness and diarrhea were reduced in cows that had previous exposure to the site. However, lameness, the primary sign, and diarrhea were resolved in all cows by the end of each trial without treatment and hair coats returned to normal by the following spring. Only 4 calves showed signs of lameness or diarrhea in the 3-year study. Cattle grazing is a viable option for the end land use plan for Highland Valley Copper, provided a CuSO4·5H2O supplement is available to counteract the toxic effects of the high-Mo forage. As well, animals with previous exposure to the site should be utilized, as they appear to develop a tolerance to the Mo in the forage.
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Vol. 59 • No. 3