| Summary: | Revegetation and sustainable cattle grazing are major objectives in the program for the reclamation of mine tailings at the Highland Valley Copper mine in British Columbia, Canada. Residual molybdenum (Mo) in the tailings is imbibed by vegetation and can accumulate to extremely high levels (> 25 ppm Mo on a dry matter basis). Accordingly, grazing studies were initiated with cattle to determine the feasibility of utilizing the Bethlehem and Highmont tailings sites for livestock production. Molybdenum levels in forages were at least ten times higher at Highmont than at Bethlehem. A total of 262 cow-calf pairs grazed the Bethlehem site for four consecutive years (1994 - 1997) and the Highmont site for five consecutive years (1998 - 2002). Cattle at Bethlehem did not show clinical signs of Mo toxicity or copper deficiency. In contrast, cattle at Highmont showed clinical signs including lameness, diarrhea and haircoat depigmentation. The onset and severity of the affliction appeared to be related, in part, to prevailing moisture conditions, which affected Mo availability in forage. The cattle recovered by the end of each trial and haircoat problems were resolved by the next spring. Preventive measures were attempted using copper supplements that can alleviate Mo toxicity. Copper boluses did not provide adequate protection in 2001 but copper sulphate supplementation in loose salt prevented the onset of clinical signs in 2002.
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