ARS | Publication request: Concentrations and apparent digestibility of lignin and carbohydrate fractions in cell walls of whole-crop cereal silages

Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2011
Publication Date: July 11, 2011
Citation: Wallsten, J., Hatfield, R.D. 2011. Concentrations and apparent digestibility of lignin and carbohydrate fractions in cell walls of whole-crop cereal silages. Journal of Dairy Science. 94(E-Supplement 1):233-234.

Technical Abstract: Whole-crop cereal silage (WCCS) of oats generally has lower fiber digestibility than WCCS of barley. When investigated more closely, the difference seems mainly to be in the digestibility of the hemicellulosic fraction (HC), where HC is calculated as neutral detergent fibre (NDF) – acid detergent fibre (ADF). A set of 27 WCCS samples of barley, wheat, and oats harvested at 3 different maturity stages, and 54 corresponding fecal samples (from dairy heifers) were analyzed for cell wall (CW) composition. Analysis included NDF, ADF and total CW recovered by washing the samples in different aqueous and organic solvents. The CW residue was used to analyze ash, acetyl bromide lignin, and neutral sugar composition. The data were analyzed with proc reg and proc mixed in SAS. The CW concentration was higher than the NDF concentration in both forages and feces. The correlation between the two fiber fractions was lower in forages (R=0.63) than in feces (R=0.94), possibly due to soluble fiber fractions that were included in forage CW, but not in the forage NDF. The lignin concentration in the silages was higher (P<0.001) in oats (111 g/kg DM) than in barley (88 g/kg DM) and wheat (91 g/kg DM). Also in the feces, oats (190 g/kg DM) had higher lignin concentration (P<0.001) than barley (168 g/kg DM) and wheat (168 g/kg DM). There was an apparent loss of 20-40% of the lignin during digestion, and the losses were higher in more immature silages. The correlation between xylose and HC concentrations was lower than expected in both forages (R= 0.63) and feces (R=0.65). However, the correlation between xylose and HC digestibilities was high (R=0.91). The high apparent digestion of lignin is probably a result of losses from the feces during analysis, rather than actual digestion in the animal. The trend with higher losses for more immature silages is of concern as that will overestimate fiber and possibly in vitro DM digestibility for these silages.