EFFECT OF HAY MATURITY, FORAGE SOURCE, OR NEUTRAL DETERGENT FIBER CONTENT ON DIGESTION OF DIETS CONTAINING TIFTON-85 BERMUDAGRASS AND CORN-SILAGE

Total mixed rations (TMRs) based on corn silage (30% DM) or Tifton 85 bermudagrass hay harvested at 3.5 and seven weeks of growth and with l ow or high neutral detergent fiber (NDF) content were used to study th e effects of hay maturity, forage source, or level of dietary NDF on i n situ digestion kinetics for TMRs. Among forages, NDF and lignin conc entrations decreased in the order of: Tifton 85 bermudagrass harvested at seven weeks of growth, Tifton 85 bermudagrass harvested at 3.5 wee ks of growth, and corn silage, while in vitro and in situ dry matter ( DM) digestion showed the opposite trend. The extent of in situ NDF dig estion decreased in the order of: Tifton 85 bermudagrass harvested at 3.5 weeks of growth, (60.1%), Tifton 85 bermudagrass harvested at seve n weeks of growth (45.6%), and corn silage (42.5%). Increase in bermud agrass maturity decreased (P<0.01) in vitro NDF disappearance for TMRs at 48 h of incubation from 44.7 to 38.8%. Forage source or the level of dietary NDF had no effect on the extent of in situ DM digestion for TMRs. Increase in bermudagrass maturity decreased (P<0.05) the extent of in situ digestion of DM and NDF for TMRs. After fitting the nonlin ear model to the disappearance data, the TMR in which corn silage was used as the forage source had higher (P<0.05) readily digestible fract ion of DM than T85 based TMRs. Digestion profiles for 3.5 weeks bermud agrass based TMRs were similar to those of corn silage based TMR, (C) 1998 Elsevier Science B.V.