Molybdenum - Cattle
It’s easy to see the toxic effect of molybdenum here. Both cattle are genetically black and both animals have low blood copper concentrations (hypocupraemia) but the black animal has been fed a diet containing iron but with no molybdenum while the depigmented animal, which appears brown, has been fed a diet including molybdenum. Animals with low blood copper may not show any symptoms of “copper deficiency” but those with molybdenum toxicity usually do. In this example the presence of molybdenum in the diet is the only difference between the two animals. Both have blood copper levels which would normally be considered deficient. It is the molybdenum which causes the symptoms of copper deficiency not low blood copper. 
Coat colour has only a minor direct effect on animal welfare and herd profitability. It is however a very good indicator of molybdenum toxicity which will be having other more serious effects.