The effect of the chemical composition of maize plant lignin on the digestibility of maize stalk in the rumen of cattle

Abstract

I. Digestibility of niaize stalk from lroyer Reid (Tr) maize and its isogenic mutant (bml) was studied by suspending nylon bags containing ground tissue in the rumen of a fistulated steer. The animal was given a grass hay-conccntrate ( 5 : 3) diet or a maize silage-grass hayconcentrate (4: I : 3) diet.2. The digestibility of the organic matter of the mutant maize stalk was greater than that ofthe normal maize stalk.3. Adaptation of the rumen to maize silage increased the organic-matter digestibility of the maize stalk.4. Lignin content was determined by two methods, namely organic matter insoluble in 72 "/, sulphuric acid (method of the Association of Oficial Agricultural Chemists, 1960) (AOAC-lignin) and the organic matter lost from the ligno-cellulose complex (rcprescnted by acid-detergent fibre) by oxidation with potassium permanganate. The AOAC-lignin concentration was twice the pcrmanganatc-lignin concentration, but the amount of ligninestimated by both methods showed a significant negative relation to organic-matter digestibility. The AOAC-lignin concentration was greater in Tr than in bm, maize but the permanganate-lignin concentration in Tr was slightly lower than in bm,. .There was an irregular relationship between the amount of lignin extractable with dimethylformamide (DNIF) and digestibility of organic matter due to the solution of some of the DMF-lignin during digestion. The loss of lignin was greater from the mutant maize stalk tissue than from the parent maize stalk tissue.6. The chemical composition of DMF-lignin determined by analysis showed a significant correlation between the syringealdehyde, p-hydroxybenzaldehyde and vanillin concentrations, and digestibility of organic matter. 7. Highcr concentrations of both phenolic aldehydes and acids wcrc found in the less digestible Tr material than in the bm, stalk tissue.Ruminants have a digestive system which enables them to utilize fibrous pIant material. However, the efficiency of utilization of the carbohydrate and protein constituents of the plant varies and is related to, among other things, the degree of lignification (Van Soest, 1967). The lowering of the digestibility of plant organic matter by lignin is believed to be caused by the physical inaccessibility of cellulose to the microbial enzymes due to lignin encrustation of the microfibrils (Sullivan, 1962), the inability of microbial enzymes to degrade the lignin polymer (Van Soest, 1966) and the inhibition of enzymes by phenolic constitucnts of lignin (Patton & Gieseker, T h e various studics which have been conducted to elucidate the relationship between lignin contcnt and forage digestibility have been reviewed by Ely, Kane, Jacobson & Moore (1953), Dehority, Johnson & Conrad (1962) Preparation of the maize stalk tissues. T h e bm, maize used in this study was introduced into the genotype of the inbred line TY by six generations of back-crosses. It is isogenic with the inbred Tr except for the bm, locus and possibly some adjacent loci. The two inbred lines were planted on 19 May 1...

Transformations of structural phenylpropanoids during cell wall digestion

“…Studies using 'H-NMR are in agreement with the previous findings but are also non-specific [175,176]. Some of these reactions have been observed in vitro with ['%]lignin cell walls [122], and in vivo with normal maize [182] and treated straw but not in untreated straw and lucerne studied with a "C-NMR method [159]. Those of some other Gramineae and of luceme are both more alkali-and more acid-soluble [ 1761. The changes in faecal phenylpropanoids appear therefore to be both quantitative and qualitative.…”

Effect of down-regulation of cinnamyl alcohol dehydrogenase on cell wall composition and on degradability of tobacco stems

“…The slight increase in rate observed for two lines and the absence of any signiÐcant di †erence in the other line are in agreement with similar variations in rates observed for bm1 maize (Cymbaluk et al 1973 ;Gordon and Neudoer †er 1973). A lower lag phase of the transgenic stems in line 50 than in the control, together with a higher rate of degradability, is predictive of a higher intake of the down-regulated plants.…”

“…Several studies have shown that the digestibility of this mutant is greater than that of the normal counterpart both in vitro and in vivo (Barrie`re and Argillier 1993). Its rate of digestibility is either the same or slightly greater than that of normal plants (Cymbaluk et al 1973). Similarly, it has been shown that the bmr6 mutant of sorghum has greater in vitro digestibility (Hanna et al 1981) and lower CAD activity than its normal counterpart (Bucholtz et al 1980) but, in this case, a slightly lower level of O-methyl transferase activity was also detected (Pillonel et al 1991).…”

Improvement of biomass through lignin modification

“…The bm1 mutant has an S/G ratio that is comparable to that of wild-type; however, its lignin includes elevated levels of coniferaldehyde and sinapaldehyde . Like the bm3 mutant, in vivo cell-wall digestibility is enhanced in the bm1 mutant, but to a lesser extent (Cymbaluk et al, 1973). Interestingly, a study using synthetic lignin and a cell-wall model system showed that coniferaldehyde-containing lignin has more of an inhibitory effect on cell-wall degradability than coniferyl alcohol-containing lignin when measured using an in vitro enzyme digestion assay (Grabber et al, 1998b).…”