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Crop Science Abstract -

Alfalfa Morphological Stage and its Relation to in Situ Digestibility of Detergent Fiber Fractions of Stems


This article in CS

  1. Vol. 29 No. 5, p. 1315-1319
    Received: Sept 29, 1988

    * Corresponding author(s):
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  1. Matt A. Sanderson ,
  2. J. S. Hornstein and
  3. W. F. Wedin
  1. Texas A&M Agric. Res. and Ext. Ctr., P.O. Box 292 Stephenville, TX 76401



A reliable index for quantifying maturity and predicting herbage quality of alfalfa (Medicago sativa L.) grown in diverse environments would be useful. An index developed at Cornell University was used to compare the in situ rate and extent of digestibility of neutral-detergent fiber (NDF), cellulose, and hemicellulose of spring~ and summer-grown alfalfa stems at similar morphological stages. Stems were harvested every 10 d during spring growth and summer regrowth of 1984 and 1985. Maturity at each harvest was classified on a scale of 0 to 9, and a mean stage number was calculated. Ground (2 mm) stems were ruminally incubated in dacron bags for 0 and h in 1984 and 0, 3, 6, 9, 12, 24, 48, and 72 h in 1985. Residues were extracted sequentially with neutral and acid detergent to determine residual NDF, cellulose, and hemicellulose. Rate of digestion (1985 data only) was calculated via nonlinear regression. After 48 h in the rumen, NDF, cellulose, and hemicellulose of spring-grown stems were digested to a greater extent than summer-grown stems of comparable chronological age. Digestibility of NDF [R2 = 0.78, root error mean square (REMS) = 64 g kg−1, cellulose (R2 = 0.78 REMS = 58 g kg−1), and hemicellulose (R2 = 0.83, REMS = 59 g kg−1) declined nonlinearly with increasing maturity stage. Digestion rate of NDF, cellulose, and hemicellulose was faster in vegetative stems (average = 0.164 h−1) compared with reproductive stems (average = 0.093 h−1). Hemicellulose was digested 80% faster than cellulose. Our data demonstrated a close association between in situ digestibility of detergent-fiber fractions and the Cornell index and further supports its utility.

Journal Paper no. J-12835 of the Iowa Agric. and Home Economics Exp. Stn., Ames, 50011. Project no. 2281. Supported in part by grants from the Graduate College and Graduate Student Senate of Iowa State Univ.

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