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

Abstract

1. Digestibility of maize stalk from Troyer Reid ( Tr ) maize and its isogenic mutant ( bm 1 ) was studied by suspending nylon bags containing ground tissue in the rumen of a fistulated steer. The animal was given a grass hay–concentrate (5:3) diet or a maize silage–grass hay–concentrate (4:1:3) diet. 2. The digestibility of the organic matter of the mutant maize stalk was greater than that of the 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 Official Agricultural Chemists, 1960) (AOAC-lignin) and the organic matter lost from the ligno-cellulose complex (represented by acid-detergent fibre) by oxidation with potassium permanganate. The AOAC-lignin concentration was twice the permanganate-lignin concentration, but the amount of lignin estimated by both methods showed a significant negative relation to organic-matter digestibility. The AOAC-lignin concentration was greater in Tr than in bm 1 maize but the permanganate-lignin concentration in Tr was slightly lower than in bm 1 . 5. There was an irregular relationship between the amount of lignin extractable with dimethylformamide (DMF) 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. Higher concentrations of both phenolic aldehydes and acids were found in the less digestible Tr material than in the bm 1 stalk tissue.