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 low or high neutral detergent fiber (NDF) content were used to study the effects of hay maturity, forage source, or level of dietary NDF on in situ digestion kinetics for TMRs. Among forages, NDF and lignin concentrations decreased in the order of: Tifton 85 bermudagrass harvested at seven weeks of growth, Tifton 85 bermudagrass harvested at 3.5 weeks 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 digestion decreased in the order of: Tifton 85 bermudagrass harvested at 3.5 weeks of growth, (60.1%), Tifton 85 bermudagrass harvested at seven weeks of growth (45.6%), and corn silage (42.5%). Increase in bermudagrass 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 nonlinear model to the disappearance data, the TMR in which corn silage was used as the forage source had higher (P<0.05) readily digestible fraction of DM than T85 based TMRs. Digestion profiles for 3.5 weeks bermudagrass based TMRs were similar to those of corn silage based TMR.