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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #69834
Title: FORAGE QUALITY VARIATION AMONG MAIZE INBREDS: IN VITRO DIGESTION KINETICS AND THEIR PREDICTION WITH NIRS

Author
item Jung, Hans Joachim
item Mertens, David
item Buxton, Dwayne

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Slow and incomplete digestion is a major factor limiting the use of high fiber crop residues, such as corn stalks, as a feed for ruminant livestock. If genetic variation for rate or extent of fiber digestion is present, it may be possible to develop corn hybrids with fiber that is more rapidly and completely digested, thus increasing the utilization of fiber and reducing production costs for ruminant livestock. A study was conducted to determin if genetic variation exists for the rate and extent of fiber digestion of corn stalks in currently used genetic sources and, if so, to determine which analytical procedures would be most efficient in selecting superior genotypes from breeding nurseries. Results of the study indicate that there is a great deal of genetic variation for both rate and extent of fiber digestion among corn inbreds and that NIRS, a rapid and inexpensive analytical process, can be used as an initial screening tool for identifying desirable genotypes. Corn silage is an important component of dairy and beef diets. An improvement in the digestibility of the vegetative part of corn silage would have a large economic impact on the livestock industry. This study points to a promising research avenue.

Technical Abstract: Forty-seven maize inbred lines were evaluated for in vitro cell wall digestion using stem internode tissue harvested at silking during 2 growing seasons. Samples were incubated under constant CO2 and sampled at 11 time points from 0 to 96 hr and the data fitted to a first-order kinetic model with a discrete lag period. NIRS prediction equations were developed to estimate residue recovery at each time and the resulting data were fit to the same mathematical model as the in vitro data. Separate NIRS prediction equations were developed for direct prediction of digestion parameters to determine the ability of NIRS to directly predict digestion kinetics. Initial NDF concentrations ranged from 465 to 699 g kg**-1 dry matter and indigestible NDF concentrations ranged from 139 to 322 g kg**-1 of dry matter. Rate of digestion (kd) among inbred lines varied from 0.026 to 0.06 h**-1 and was correlated with initial NDF concentrations (r=0.52) and indigestible NDF concentration (r=0.44). The low correlations between kinetic parameters suggest that composition of the NDF fraction is as important as the concentration of NDF in regulating fiber digestion of maize. The relationships between direct NIRS prediction and in vitro data for indigestible NDF (r=0.89) and kd (r=0.68) were similar in magnitude to the relationships observed when NIR was used to estimate residues at individual time points and the resulting data fitted to the non-linear regression model to calculate INDF (r=0.94) and kd (r=0.60). These data suggest that it should be possible to simultaneously improve the rate and extent of NDF digestion and NDF concentration of maize inbreds through genetic selection and that NIRS may serve as an initial screening tool for identifying superior genotypes for more thorough in vitro testing.