Animal response to grazing on reclaimed mine tailings
In 1994 and 1995, 32 cow/calf pairs were grazed on molybdenum (Mo) enriched herbage (21-65 mg kg"¹ DM) for a 12 week period at a reclaimed mine site located at the Highland Valley Copper Mine near Logan Lake, British Columbia. The scientific literature indicates that feedstuffs with high levels of Mo (>10 ppm) may induce a copper (Cu) deficiency in ruminants (referred to as molybdenosis), which results in poor animal health and productivity and may result in death of affected animals. This
... was undertaken to evaluate the efficacy of grazing cattle on Mo enriched forage on reclaimed mine tailings, with or without an All-Trace copper-enriched bolus supplement, and its effects on Cu and Mo levels in milk, blood and liver tissue. Weight gains and health were normal for all the animals and no visual signs of a Mo induced Cu deficiency were observed. Serum Cu concentrations remained in the normal range of 0.7 to 1.5 ug ml"¹ and did not differ (P<0.05) for the supplemented and control groups for cows or calves in either year. Liver tissue Cu concentration increased in the Cu supplemented cows and calves for the first sampling period after treatment but was in the normal range throughout the remainder of the season for both treatment groups. Copper supplementation did not affect the concentrations of Mo in the serum, liver tissue, or milk; however, Mo did accumulate linearly in these components throughout the grazing period. Our results to date suggest that prolonged periods of Mo-enriched herbage consumption will result in increased concentrations of Mo in the serum and liver tissue of cows and calves but this may not result in molybdenosis when the Cu requirements of the animals are met. Supplementing animals with Cu-enriched boli enhanced liver Cu storage, while the effects on serum and milk Cu were minimal.