Copper balance in mature geldings fed supplemental molybdenum

Four mature sedentary geldings were used in a 4x4 Latin square designed exp eriment to evaluate the effects of supplemental molybdenum (Mo) on copper ( Cu) balance. Four diets were formulated to contain 0 (control), 5, 10 and 2 0 ppm of supplemental Mo and were fed for a 21-day adjustment period follow ed by a 72-hour fecal and urine collection. Diets consisted of a pelleted c oncentrate 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 formulate d to be isonitrogenous and isocaloric with similar concentrations of Cu. Ur ine was collected every four hours for 72 hours and multiple fecal grab sam ples 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 p ost feeding, and eight hours post feeding for serum Cu analysis. Balance da ta were analyzed using a general linear model procedure with horse, period and treatment as main effects. Serum Cu data were analyzed using the genera l linear model procedure with horse, treatment and period as main effects a nd time as the repeated variable. The intake of Cu was similar among all di ets fed. There was no difference (p>.05) in serum Cu concentrations over ti me or between treatments due to supplemental Mo. Urinary and fecal excretio n 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 highe r (p<.05) in horses fed the 20 ppm Mo diet versus the 0, 5 and 10 ppm Mo di et. As Mo intake increased, fecal excretion increased (p<.05) across all di ets. 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 advers e effect on the absorption and retention of Cu when fed to mature geldings.