Copper-molybdenum interactions in ruminant nutrition and reproductive physiology: mechanistic insights into growth, digestibility, and follicular development

The copper-molybdenum-sulfur (Cu-Mo-S) interaction is one of the most important mineral antagonisms in ruminant nutrition because it can induce functional copper deficiency even when dietary copper intake appears adequate. In the rumen, dietary sulfur is reduced to sulfide, which reacts with molybdate to form thiomolybdates. These compounds bind copper within ruminal digesta and, when produced in excess, may also enter the circulation and interfere with systemic copper trafficking and cuproenzyme function. This review critically synthesizes evidence on ruminal thiomolybdate formation, post-absorptive copper sequestration, growth and immune consequences, rumen fermentation, and hair/wool follicle abnormalities. Practical mitigation requires more than increasing dietary copper: feed, forage, mineral supplements, and drinking water should be analyzed together for Cu, Mo, S, Fe, and Zn; dietary Cu:Mo:S balance should be interpreted in a species-specific manner; high Mo and sulfur exposure should be reduced when possible; and copper supplementation should be adjusted cautiously, particularly in sheep because of their narrow margin between deficiency and toxicity. Rumen-stable or less rumen-soluble copper sources, such as hydroxychloride or selected organic copper complexes, may reduce ruminal antagonism under specific feeding conditions, although responses remain diet- and species-dependent. Diagnostic interpretation should combine serum copper, liver copper, ceruloplasmin or SOD-related indices, and, where available, functional biomarkers such as CCS or TCA-fractionated plasma copper. The review concludes that effective management of Cu-Mo-S imbalance requires an integrated framework linking diet and water testing, functional copper-status assessment, species-specific risk thresholds, and targeted supplementation rather than broad group-average mineral feeding.