Ruminal Solubility and Bioavailability of Inorganic Trace Mineral Sources and Effects on Fermentation Activity Measured in Vitro

The aim of this study was to assess the effects of supplementation with inorganic sources of manganese (MnO, MnSO4), zinc (ZnO, ZnSO4) and copper (CuSO4) at different levels (0.06%DM for Mn, 0.05%DM for Zn; 0.01 and 0.05%DM for Cu) on in vitro rumen fermentation, solubility and bioavailability. Fermentation activity was measured by total gas production (TGP) and dry matter degradability after 70 h of fermentation (dDM%). Trace mineral (TM) solubility was estimated via the TM concentration in the supernatant of the final fermentation medium (SOL) and TM bioavailability from the TM concentration in a bacterial-enriched fraction (BACT). Mn (regardless of source) and ZnO tended (p < 0.10) to decrease, while Cu showed no significant effect on TGP. The addition of inorganic Mn and of ZnO tended (p < 0.10) to decrease, ZnSO4 tended to increase (p < 0.10), whilst Cu showed no effect on dDM%. Concerning solubility, Mn (MnO and MnSO4), ZnSO4 and CuSO4 significantly (p < 0.05, p < 0.001 and p < 0.01) increased, while ZnO did not affect TM content in the SOL. These results indicate that MnSO4, ZnSO4 and CuSO4 are highly soluble, MnO is quite soluble, while ZnO has a low solubility in the rumen. Based on the TM content in BACT, MnO, MnS4 and CuSO4 have high bioavailability, while ZnO is poorly assimilated by rumen bacteria. However, the lack of clear inhibition or improvement in fermentations suggests that the rumen microbiota have a low requirement for TM supplementation.