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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #102928
Title: IMPACT OF ACCESSIBILITY AND CHEMICAL COMPOSITION ON CELL-WALL POLYSACCHARIDE DEGRADABILITY OF MAIZE AND LUCERNE STEMS

Author
item Jung, Hans Joachim
item JORGENSEN, MATTHEW - UNIVERSITY OF MINNESOTA
item LINN, JAMES - UNIVERSITY OF MINNESOTA
item ENGELS, FERDINAND - WAGENINGEN AGRIC UNIV

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Manure production is increased and milk and meat production efficiency are reduced when the digestibility of fiber in forage crops by cattle is low. Although fiber digestibility of immature forages is high, yield of most forages increases with maturity. Therefore, genetic improvement of fiber digestibility in mature forage crops is needed to improve animal production nefficiency, decrease manure output, and maximize farm profitability. Inability to identify the appropriate laboratory marker for fiber digestiblity limits progress on genetic improvement of forages. Using a group of alfalfa and corn plant samples of different genetic potential for fiber digestibility, it was shown that the anatomical structure of these forages limits fiber digestibility and that chemical composition is a poor predictor of digestibility. This result is unfortunate because measurements of chemical composition could easily be incorporated into a commercial plant breeding program to improve forages, whereas measurement of anatomical differences is very time consuming and expensive. This research will be of value to other scientists evaluating laboratory markers for fiber digestibility because the results demonstrate the necessity of developing simple anatomical markers for improved fiber digestibility.

Technical Abstract: Although lignification of forages is generally accepted as limiting cell- wall degradability, prediction of degradation from wall composition is difficult when forages are of similar maturity. It has been proposed that microbe accessibility to potentially degradable walls is limited by the presence of non-disrupted cells in forage particles with lignified primary walls acting as barriers to microbial access. We tested this accessibility hypothesis by evaluating the impact of reducing particle size of maize and lucerne stems to the level of individual cells by ball-milling in order to eliminate accessibility as a limiting factor. Although wall concentration and composition were not influenced by ball-milling compared to grinding to pass a 1-mm screen in a cyclone-type mill, degradability of wall polysaccharides was dramatically increased. However, only those polysaccharides (cellulose and xylan) that are most abundant in cell types with lignified primary and secondary walls increased in degradability due to particle size reduction. Degradability of pectins, which are abundant in non-lignified tissues in lucerne, did not respond to ball-milling. Contrary to our expectations, ball-milled forages showed fewer correlations for wall composition with degradability than observed for the larger particle size grinding treatment. Many components of the wall were correlated with polysaccharide degradation for the cyclone ground samples; however, the results were inconsistent as to which wall components were correlated with degradation among and within forages.