Abstract #T239

# T239
Relationship of NDFD24 and uNDF240 to NDF components and the impact of maturity on predicted digestible energy of corn plants harvested at silage maturity.
B. Powel-Smith1, M. Laubach1, T. Hageman1, D. Bolinger1, B. Mahanna1, L. Nuzback1, F. N. Owens*1, 1DuPont Pioneer, Johnston, IA.

Components of NDF (hemicellulose, cellulose, and lignin) differ in digestibility. How plant maturity alters subcomponents and changes in vitro NDF digestibility and uNDF240 interests plant breeders. Silage producers need more data on the impact of plant maturation on NDF components, starch content, digestibility, and yield. One commercial Pioneer silage hybrid was grown on 6 farms in the upper Midwest. Six plants from 2 diverse locations within each farm were harvested at silage maturity (26 to 38% plant DM). Divided into ear and non-ear fractions, plants were dried and assayed or proportionally recombined and assayed at a commercial lab. Based on within-farm replicate silages, differences among farms were detected (P < 0.05) in whole plant dry weight and in NDF, ADF, starch, cellulose, and lignin contents. Farms did not differ significantly in NDFD despite a range of 52 to 62%. Covaried by plant DM content, only lignin remained different (P < 0.03) among farms as greater (P < 0.01) starch diluted (P < 0.05) NDF, ADF, potentially digested NDF (1 – uNDF240), and cellulose. NDFD24 was related (P < 0.01) negatively to uNDF240 but positively to hemicellulose as a fraction of NDF; NDFD240 was related (P < 0.01) negatively to uNDF but positively to digestible NDF (NDFD24 x NDF). With components expressed as a fraction of NDF, hemicellulose increased whereas cellulose and lignin decreased (P < 0.03) as plant DM increased reflecting NDF compositions of ear and non-ear plant portions. By multiple regression, NDFD24 and NDFD240 were more responsive to hemicellulose than to cellulose or lignin as a fraction of NDF (slopes of 0.93, 0.33, and 0.03; 0.90, 0.66, and 0.42) reflecting digestibility differences. With regressions forced through zero, uNDF240 increased by 2.1, 6.6, and 4.6 percentage points for each 1% increased plant lignin. Based on constant NDFD24, decreased NDF, and increased starch content (assuming 94% starch digestibility), digestible DM increased (P < 0.02) 0.42% per kg and 1.84% per hectare for each 1% increase in corn plant DM. Delayed harvest within the corn silage DM window increases available energy content of and yields from corn plants.

Key Words: corn plant maturity, NDF digestion, NDF components