150. Ruminal Microbial Efficiency and Fermentation Characteristics Modeled by the Addition of Methionine, Bound Zn-methionine, or Zinc Sulfate in a Continuous Culture System.

Abstract

The effects of zinc source and additional amino acid on ruminal microbial efficiency and ruminal fermentation characteristics were evaluated. A continuous culture system using ten 1-L dual-flow fermenter chambers (experimental units) were used during three 5-d batches. A generalized complete block design (block = batch) used 3 d for adaptation and 2 d for collections. Treatments were formulated as follows: 1) CONTROL, DI-water; 2) ZnSO4, zinc sulfate [514 mg of zinc/chamber-daily]; 3) ZnMet, zinc-methionine complex [514 mg of zinc +1,004 mg of DL-Methionine/chamber-daily]; 4) DL-Met, DL-Methionine [1,004 mg of DL-Methionine/chamber-daily], and  5) ZnSO4+DL, zinc sulfate plus DL-Methionine added separately (same doses). Two ruminally cannulated steers (BW = 400 ± 50 kg) receiving a steam-flaked corn-based finishing diet were used. Data was analyzed using treatment, time, and interaction as fixed effects and batch as the random effect. The DL-Met treatment tended to be greater than ZnMet (P = 0.11), while not different (P = 0.91) from ZnSO4+DL (treatment × time interaction, P = 0.03). Ammonia-N from ZnSO4-treated chambers (no added DL-Methionine) was not different (P = 0.32) from ZnMet. Chambers receiving the DL-Methionine had greater (P < 0.04) microbial organic matter flow, total N flow, microbial N flow, and microbial efficiency than ZnMet, ZnSO4+DL, ZnSO4, and Control treatments. The ZnSO4 tended (P = 0.13) to increase microbial efficiency compared to ZnMet, while ZnMet × ZnSO4+DL did not differ (P = 0.66). Treatments containing unbound zinc (ZnSO4+DL and ZnSO4) had lower (P < 0.01) total N flow through the chamber. Total volatile fatty acids increased (P ≤ 0.02) for ZnSO4+DL, while acetate:propionate ratio was not affected (P = 0.20). Chambers receiving ZnSO4+DL tended (P = 0.06) to have lower acetate compared to ZnMet and DL-Met, while greater (P ≤ 0.02) butyrate. Average pH decreased (P = 0.01) for ZnSO4 compared to DL-Met. The ZnSO4+DL had a greater (P = 0.03) max pH compared to ZnMet, while a tendency (P = 0.06) was also observed for ZnSO4 to induce the smallest minimum pH. The ZnSO4 showed greater time (P = 0.01) and tended (P = 0.07) for greater area below pH 5.0 compared to ZnMet, while ZnSO4+DL chambers did not differ (P ≥ 0.50) from ZnMet. The DL-Methionine treatment improved ruminal microbial efficiency, except with the combination of excessive ZnSO4 or when Zn was present but not available (ZnMet). The ruminal microbial efficiency during the in vitro model for either bound or ruminally available Zn was not improved in the presence of additional amino acids. For the complex Zn-methionine, such an effect was due to its ruminal-unavailable nature, while ZnSO4 was due to changes in ruminal fermentation characteristics.