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

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,. 5 . 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.