Molybdenum (Mo) is a micronutrient (trace mineral) necessary for life with no deficiency symptoms ever reported in cats or dogs.
Foods rich in molybdenum include lentils, legumes (dried peas, soybeans as well as in beans (kidney, lima, pinto beans and Garbanzo beans), barley, oats, nuts (almond and cashews), yogurt, eggs, liver, whole grains, and tomatoes.
In human beings, the sulfite oxidase, xanthine oxidase, mitochondrial amidoxime reducing component (marc), and aldehyde oxidase enzymes require it. These enzymes help in breaking down various toxins and waste products from the body.
In felines, the AAFCO does not list this mineral as one of the essential nutrients for optimal grown and development in these animals. However, the NRC mentions it as one of the micronutrients for cats that help enzymes to work properly.
On effects of deficiency, an article published on Frontiers in Neurology notes that “molybdenum deficiency predisposes mammals to CNS disease because it inactivates both xanthine oxidase-dehydrogenase (the enzyme barrier that protects the CNS from dietary purine loading) and sulfite oxidase (the enzyme barrier that protects the CNS from dietary sulfite loading).”
Finally, molybdenum poisoning has been noted in ruminants, especially cattle as opposed to non-ruminants where it induces among other things copper deficiency.
More research needs to be done on the essence of these micro-nutrients and whether it should be included in diets or not.