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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #120705
Title: WHY DIGESTIBILITY OF ALFALFA STEMS DECLINES WITH MATURITY

Author
item Jung, Hans Joachim
item ENGELS, F - WAGENINGEN UNIVERSITY

Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/24/2001
Publication Date: 7/25/2003
Citation: JUNG, H.G., ENGELS, F.M. WHY DIGESTIBILITY OF ALFALFA STEMS DECLINES WITH MATURITY. JOURNAL OF DAIRY SCIENCE. 2003. V. 84 (SUPPL. 1): ABSTRACT P. 155.

Interpretive Summary:

Technical Abstract: Development of an alfalfa stem internode from three genotypes was examined to determine why digestibility of alfalfa stems declines with maturity. The seventh internode from the stem base was collected from replicated field plots at five stages of development (12, 17, 21, 31, and 87 d of summer regrowth). Internode samples were preserved in alcohol for microscopic analysis and freeze-dried for cell wall (CW) and in vitro digestibility analysis. While minor genotypic differences were noted, the general pattern of development and digestibility was similar for the genotypes so only means are presented. Young, elongating internodes (12 and 17 d) had thin, nonlignified CWs in all tissues except primary xylem vessels which were already lignified. Internode elongation was complete by 21 d of regrowth, at which time there was some deposition of xylem fibers and this tissue was lignified. Further maturation (31 and 87 d) consisted of xylem tissue proliferation by cambial activity, and lignification of primary phloem and pith parenchyma tissues. CW concentration increased with maturity. Pectin (Pec) concentration declined while cellulose (Cel), hemicellulose (Hemi), and lignin (Lig) all increased with maturation. Major CW changes occurred when internode elongation ceased. All alfalfa stem tissues were completely digested for the two youngest maturity stages, except primary xylem vessels. Xylem fiber remained undigested after 21 d of regrowth and amount of undigested xylem increased with maturity. Some primary phloem and pith parenchyma tissues were undigested in the two oldest samples. CW polysaccharide digestion declined steadily from 17 to 87 d of regrowth. Xylem fiber was lignified as soon as it was formed and was almost completely indigestible.