EFFECTS OF FIBER FROM TROPICAL CORN AND FORAGE SORGHUM SILAGES ON INTAKE, DIGESTION, AND PERFORMANCE OF LACTATING DAIRY-COWS

Tropical corn silage was compared with sorghum silage as a basal forag e in the diets of high producing dairy cows. Sorghum and tropical corn silages were each included in place of ground corn at incremental con centrations in the experimental diets. Eight separate diets were fed, four diets containing each silage ranging in forage neutral detergent fiber (NDF) from approximately 25 to 31% and ranging in total NDF from approximately 41 to 45%. Diets were arranged in a 2 x 4 factorial des ign and were fed to lactating cows (n = 24; pretrial mean milk product ion = 39 kg/d; body weight = 656 kg; and days in milk = 81). As concen trations of dietary NDF increased, intake and milk production decrease d linearly. The impact of dietary NDF on intake was greater for diets based on tropical corn silage than for diets based on sorghum silage. Energy intake and milk production were reduced, but cows consumed more fiber when challenged with higher dietary concentrations of fiber. Th e in vitro rate and extent of digestion of dietary samples were correl ated with intake response. The rate of in vitro fiber digestion was sl ower for samples that contained tropical corn silage than for samples that contained sorghum silage. In vivo digestibility measurements were influenced by intake and dietary composition. Results of this trial i ndicated that sorghum silage can have equal or slightly greater nutrit ional value than tropical corn silage when these forages are fed at eq ual concentrations of dietary fiber.