Molybdenum Exposure in Drinking Water Vs Feed Impacts Apparent Absorption of Copper Differently in Beef Cattle Consuming a High-Forage Diet.

Twelve Angus steers were utilized to investigate the influence of molybdenum (Mo) in drinking water or feed on apparent absorption and retention of copper (Cu) and Mo. Steers were fed a low-quality grass hay diet for 14 days. Steers were then housed in individual metabolism stalls and blocked by body weight and dry matter intake (DMI) and randomly assigned within block to one of three treatments. Treatments consisted of (1) control (no supplemental Mo), (2) 5.0 mg Mo/kg DM from sodium molybdate dihydrate (Mo-diet), and (3) 1.5 mg Mo/L from sodium molybdate dihydrate delivered in the drinking water (Mo-water). Total fecal and urine output were then collected for 5 days. Dry matter, Cu and water intake, and DM digestibility were similar across treatments. Molybdenum intake was greater (P < 0.05) in Mo-water and Mo-diet steers when compared to controls but similar between Mo-water and Mo-diet steers. Apparent absorption and retention of Cu were greater (P < 0.05) in controls when compared to Mo-diet supplemented steers. Apparent absorption and retention of Cu in steers in the Mo-water treatment did not differ from controls or those receiving the Mo-diet. Molybdenum-diet and Mo-water supplemented steers had similar apparent absorption and retention of Cu. Apparent absorption and retention of Mo (% of Mo intake) was greater in controls when compared to Mo-supplemented steers. These data indicate that Mo consumed in water may impact Cu absorption and retention to a lesser extent than Mo supplemented in the diet.