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

Abstract

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.

Ruminant Trace Minerals Deficiency and the Potential Link Between the Source and Rumen Interaction. A Review

“…In a recent in vitro study [67], the ruminal solubility of ZnSO4 was significantly higher when compared to ZnO (32 and 25 %; p < 0.05). Furthermore, of the total analyzed Zn (sum of total Zn in different fraction of the centrifuged rumen fluid), 27 to 38% and 19 to 24% for ZnSO4 and ZnO, respectively, was found in the bacteria enriched fraction, indicating not only that Zn might be assimilated by rumen bacteria, but also a higher ruminal bioavailability of ZnSO4 when compared to ZnO.…”

“…Next, the ruminal solubility of a specific TM may be expressed as an absolute value (based on the TM concentration of the supernatant) or a relative value (related to a sulfate TM, considered as 100 % rumen soluble). In recent studies [67,68], the ruminal solubility of various minerals was assessed based on a separation of the final fermentation medium (after 70 hours of fermentation) by multiple centrifugations: at 100 x g (5 minutes at 4 0 C), to separate an insoluble fraction (containing feed particles, protozoa and insolubilized minerals); the obtained supernatant is then further centrifuged at 18,500 x g (20 minutes at 4 o C) to separate a bacteria enriched fraction and a final supernatant, containing only solubilized minerals; the mineral concentration of each centrifugation fraction is then analyzed. Next, the ruminal solubility of TM can be expressed as a percentage of solubilized mineral in the final supernatant (based on the total mineral analyzed in the different centrifugation fractions.…”

“…In a study by Areolovich et al [69], the addition of 100 mg/DM of Mn (as MnCl2) significantly increased DM degradation, without affecting volatile fatty acids (VFA) concentration. In a more recent study [67], an overall negative effect of Mn (600 mg/kg DM as MnO or MnSO4) was registered: decrease of total gas production, DM degradability and butyrate (% of total VFA) concentration. Table 5 presents the effects on rumen fermentation of some Mn sources.…”

“…In an in vitro study, the solubility of CuSO4 in rumen fluid was found to be high, given that >50% of the total additional Cu was found in a final supernatant obtained after centrifugation of the final fermentation medium. Furthermore, approximately 18 to 27% of the supplemented Cu was analyzed in a bacteria enriched fraction, indicating that Cu might be assimilated by rumen bacteria [67].…”

“…In a similar study, supplementing rumen cannulated steers with 60 mg/kg DM of Mn (as MnSO4 or Mn-Hyd), the ruminal solubility of MnSO4 showed no difference when compared to Mn-Hyd (relative solubility of approximately 65 and 66 % for MnSO4 and Mn-Hyd, respectively) [62]. In an in vitro study, the ruminal solubility of two inorganic Mn sources (MnSO4 and MnO) was assessed [67]. Results showed that MnSO4 and MnO are equally soluble in the rumen fluid after 70 hours of fermentation.…”