Chemical and in vivo evaluation of a brown midrib mutant of Zea mays. I. Fibre, lignin and amino acid composition and digestibility for sheep.

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AbstractTwo types of corn (maize) were used which were genetically identical except for a mutant gene (bm1) in one which reduced the type and amount of lignin produced compared with the normal plant (Tr). The Tr plant appeared to have only slightly lower digestibilities of dry matter and fibre for sheep even though the protein contents of the cornstalks, normally less in the Tr, were equalised by supplementation with soya bean protein. Comparing the acid‐detergent method of fibre and lignin determination with an acid‐pepsin method revealed that the former method gave values considerably lower than the latter. The alkali—lignin contents of the bm1 were higher than the acid—detergent lignins which must under‐estimate the true lignin content. The acid—pepsin method gave fibre and lignin concentrations which were more closely correlated with rumen digestion of the diets as shown by dry matter loss of the diets suspended into the rumen in nylon bags. This technique also revealed there was a significant increase in the rate of rumen digestion after 69 to 74 h of incubation. Digestion of lignin on the Tr diet could be explained by loss of ferulic and p‐coumaric acids. The reduced lignin and p‐coumaric acid content of the bm corn was associated in young plants with a low phenylalanine content but normal tyrosine content suggesting that the genetic block in lignin synthesis in this plant may occur between prephenic acid and phenylalanine.