BROWN MIDRIB-3 VERSUS NORMAL CORN PLANTS (Zea mays L.) HARVESTED AS WHOLE PLANT OR STOVER AND FROZEN FRESH OR PRESERVED AS SILAGE FOR SHEEP

Brown midrib (bm) mutants of corn contain less lignin than normal (N) corn. No previous research has compared whole plant and stover of bm and N corn plants. Corn plants from N and isogenic mutant bm3 were harvested as whole plant (WP) or stover (St), and stored fresh frozen (F) or as fermented silage (S). A 2 × 2 × 2 factorial arrangement was used for the factors of mutant type (bm3 and N), plant portion (WP and ST) and storage method (S and F). A 9-day metabolism study was conducted, with 32 wethers assigned to the following forage combinations: (1) bm3WPS; (2) bm3StS; (3) NWPS; (4) NStS; (5) bm3WFF; (7) NWPF; and (8) NStF. Lignin content of bm3 forages was about 2 percentage units less than that of their N counterparts. Digestibilities of dry matter (DM), energy, acid and neutral detergent fiber (ADF and NDF) and cellulose were greater for the bm3 forages and intakes of digestible nutrients were 20–25% higher for those forages. These findings were attributed to the reduced and altered lignin of bm3. Comparison of WP and St showed that DM digestibility, DM intake (DMI), digestible DMI and digestible energy and crude protein intakes were greater for WP than for St. Differences between storage methods were not significant. A plant type by storage method interaction was found for the apparent digestibility of NDF, ADF, cellulose and energy, and for the intake of digestible NDF and ADF. These measurements decreased for WP and increased for St with ensiling. The increase in St digestibility could have been due to partial degradation of the cell wall, while the decrease in WP digestibility could have been due to a larger loss of NDF and soluble carbohydrates during fermentation. Tendencies existed for the feeding value of bm3St (F and S) to surpass that of NSt (F and S) and to approach the feeding value of NWP (F and S).