Molybdenum deficiencies are very rare. Toxicity occurs above 3 parts per million (ppm) due to reduced copper absorption, resulting in a copper deficiency. The copper level must be four times the molybdenum level to overcome this effect. High dietary levels of molybdenum are usually related to soil content. Molybdenum, like ammonium tetrathiomolybdate, is often used to treat copper toxicity in animals.
Reference: Hart, S. 2008. Meat Goat Nutrition. Pages 58-83 in Proc. 23rd Ann. Goat Field Day, Langston University, Langston, OK.