Nutritional evaluation and ruminal fermentation patterns of kochia compared with alfalfa and orchardgrass hays and ephedra and cheatgrass compared with orchardgrass hay as alternative arid-land forages for beef cattle in two dual-flow continuous culture system experiments

摘要

The objective was to evaluate the ruminal fermentation patterns of forage kochia (>FK) compared with alfalfa hay (>AH) and orchardgrass hay (>OH) (Exp. 1), and ephedra (>EPH) and immature cheatgrass (>CG) compared with OH (Exp. 2), using a dual-flow continuous culture system. Two in vitro experiments were conducted, and in each experiment, treatments were randomly assigned to six dual-flow fermenters (1,223 ± 21 mL) in a replicated 3 × 3 Latin square design, with three consecutive periods of 10 d each, consisting of 7 d for diet adaptation and 3 d for sample collection. Each fermenter was fed a total of 72 g/d (DM basis) and treatments were as follows: Exp. 1: 1) 100% OH, 2) 100% AH, and 3) 100% dried FK. Exp. 2: 1) 100% OH, 2) 100% dried CG, and 3) 100% dried EPH. On day 8, 9, and 10, samples of solid and liquid effluent from each fermenter were taken for digestibility analysis, and subsamples were collected for NH3-N, VFA, and bacterial N determinations. Data were analyzed using the MIXED procedure of SAS. In Exp. 1, treatments did not affect DM, OM, and NDF digestibilities, total VFA and molar proportions of acetate, propionate, butyrate, and branched-chain VFA. True CP digestibility, ruminal NH3-N concentration, and total N, NH3-N, NAN, and dietary N flows (g/d) were greater (P < 0.05) for FK compared with the other forages. However, treatments did not affect bacterial efficiency. In Exp. 2, DM, OM, and CP digestibilities were greater (P = 0.01) for EPH, and NDF digestibility was greater (P < 0.05) for EPH and CG compared with OH. Ephedra had the highest (P < 0.05) pH and acetate:propionate ratio and the lowest (P < 0.05) total VFA concentration. Total VFA, ruminal NH3-N concentration, and NH3-N flow (g/d) were highest (P < 0.05) for CG. Total N flow and bacterial efficiency were highest (P < 0.05) for OH and CG, while the flows (g/d) of NAN, bacterial N, and dietary N were greater (P < 0.05) for OH compared with the other forages. Results indicate that when compared with AH and OH (Exp. 1), FK has similar ruminal fermentation patterns and may be an adequate alternative for beef cattle producers. Furthermore, when compared with OH (Exp. 2), immature CG may also be an adequate forage alternative. This is especially important for areas in which conventional forages may not grow well such as the U.S. arid-land. However, EPH should not be used as the sole forage due to its poor ruminal fermentation as evidenced by the lowest total VFA concentration and propionate molar proportion.