Effect of varying calcium and phosphorus level on manganese utilization

Two experiments were conducted to evaluate the effect of varying levels of excess Ca and P on manganese (Mn) utilization. The criterion used to study the Mn-antagonizing effects of excess Ca and P was the regression of total tibia Mn on supplemental Mn intake. In Experiment 1, high supplemental levels of Mn were fed (0, 500, and 1,000 mg Mn per kg); in Experiment 2, lower Mn levels were fed (0, 50, and 100 mg Mn per kg). Supplements were added to a corn-soybean meal diet containing 1.1% Ca, .7% (.5% available) P, and 37 mg Mn per kg. In Experiment 1, a 3 x 3 x 3 factorial arrangement of treatments (four replicates) was used. Treatments were as follows: 0, .5, and 1.0% excess Ca as feed-grade ground limestone; 0, .4, and .8% excess P as KH2PO4; and 0, 500, and 1,000 mg Mn per kg as MnSO4.H2O. Total tibia Mn was depressed by P (P less than .0001) but not by Ca (P greater than .05). Compared with the standard (no added P), .4% P reduced Mn utilization by 22%, whereas .8% P reduced it by 38%. Manganese supplementation was found to ameliorate the growth-depressing effect of .8% supplemental P. Results of Experiment 2 agreed with the results in Experiment 1, providing evidence that bioavailability estimates obtained from experiments containing high levels of Mn can be extrapolated to diets containing lower levels. Results from Experiment 2 indicated that, relative to the standard (no added P), .22, .44 and .88% excess P reduced Mn utilization by 16, 22 and 31%, respectively.