Copper balance in mature geldings fed supplemental molybdenum

Abstract

Four mature sedentary geldings were used in a 4×4 Latin square designed experiment to evaluate the effects of supplemental molybdenum (Mo) on copper (Cu) balance. Four diets were formulated to contain 0 (control), 5, 10 and 20 ppm of supplemental Mo and were fed for a 21-day adjustment period followed by a 72-hour fecal and urine collection. Diets consisted of a pelleted concentrate based on corn, soybean meal and cotton seed hulls fed in a 50:50 ratio of concentrate to native prairie grass hay. All diets were formulated to be isonitrogenous and isocaloric with similar concentrations of Cu. Urine was collected every four hours for 72 hours and multiple fecal grab samples were taken every two hours post feeding. On the third collection day, blood samples were drawn at the time of feeding, each hour for five hours post feeding, and eight hours post feeding for serum Cu analysis. Balance data were analyzed using a general linear model procedure with horse, period and treatment as main effects. Serum Cu data were analyzed using the general linear model procedure with horse, treatment and period as main effects and time as the repeated variable. The intake of Cu was similar among all diets fed. There was no difference (p>.05) in serum Cu concentrations over time or between treatments due to supplemental Mo. Urinary and fecal excretion of Cu did not differ (p>.05) between diets. Consequently, the balance of Cu was similar among diets consumed. Excretion of Mo in the urine was higher (p<.05) in horses fed the 20 ppm Mo diet versus the 0, 5 and 10 ppm Mo diet. As Mo intake increased, fecal excretion increased (p<.05) across all diets. Additionally, Mo balance was higher (p<.05) on the 20 ppm Mo diet than all other diets. In conclusion, supplemental Mo appeared to have no adverse effect on the absorption and retention of Cu when fed to mature geldings.