Effects of molybdenum and sulfur on digestion by steers

Effects of Mo and S on the digestion of dietary DM, ash, OM, NDF, CP, and nonprotein OM were evaluated using four Holstein steers, each with cannulas in the rumen, proximal duodenum (PD), and terminal ileum (TI). Steers were continuously fed diets with high (13.3 mg/kg DM) and low (1.8 mg/kg DM) Mo (HM and LM, respectively) and high (3.9 g/kg DM) and low (1.3 g/kg DM) S (HS and LS, respectively) as combinations LMLS, LMHS, HMLS, and HMHS in a 4 x 4 Latin square design. Daily flows of dietary components at the PD and TI and as fecal excretion were estimated using dysprosium as an inert marker. With HM diets, the balance between absorption and endogenous input in the stomach was such that there was a lower (P less than .10) net (intake minus duodenal flow) output of mineral from the stomach. A lower (P less than .10) net output of diaminopimelic acid as an indicator of bacterial CP and DM was associated with a lower (P less than .10) net output of CP from the stomach of steers fed HM diets. This lower net output of CP from the stomach, coupled with no effect (P greater than .10) of Mo on CP in the small intestine, indicated that less CP was absorbed from the small intestine. Supplemental Mo in association with S appeared to prevent (P less than .10) an apparent higher net output of methionine from the stomach when supplemental S alone was in the diet. Effects of supplemental S were minor compared with those of supplemental Mo. Dietary Mo had negative effects on ash as an indicator of mineral balance in the stomach of steers and on the output of CP as bacterial CP and of DM of bacterial origin from the stomach of steers.