FORAGE QUALITY VARIATION AMONG MAIZE INBREDS - IN-VITRO FIBER DIGESTION KINETICS AND PREDICTION WITH NIPS

The nutritive value of forage maize (Zea mays L.) may be improved thro ugh genetic selection for increased rate of fiber digestion or decreas ed indigestible fiber concentration. To identify sources of genetic va riation, 45 maize inbreds were evaluated for in vitro neutral detergen t fiber (NDF) digestion kinetic parameters using stem internode tissue harvested at silking during 2 yr. Near infrared reflectance spectrosc opy (NIRS) was also used to estimate NDF digestion kinetic parameters. Maize inbreds varied significantly in NDF concentration and digestion kinetic parameters using either conventional in vitro analysis or NIR S predictions. Using MRS predictions, inbreds varied in NDF concentrat ion from 497 to 662 g kg(-1) dry matter (DM), rate of NDF digestion ra nged from 0.037 to 0.077 h(-1), and extent of NDF digestion was 525 to 735 g kg(-1) NDF. The ranges for NIRS predicted parameters were less than those observed for the calibration data set by conventional analy sis. Correspondence between conventional analysis data and PI;IRS pred ictions were good, except for lag time. Digestion kinetics calculated from NIRS predicted residues provided more precise predictions of lag time and fractional rate of digestion when compared with observations derived from conventional analyses, than did direct prediction of thes e kinetic parameters. Correlations between rate of NDF digestion and 1 8-h NDF digestibility (r = 0.79) or between potential extent of NDF di gestion and 96-h NDF digestibility (r = 0.95) were large enough that t hese two fermentation intervals might substitute for conducting comple te digestion kinetic studies with eight to 10 fermentation times. The substantial genetic variation among these maize inbreds shows good pot ential for development of silage hybrids with improved fiber digestion parameters. Year and year x genotype interactions were significant su ggesting that identification of superior inbred lines will require eva luations in multiple environments.