Relationships Between Crude Protein and Determination of Nondispersible Lignin

Abstract

The objective of this study was to examine the relationships between crude proetin (CP), acid detergent fiber (ADF), ADF CP, and acid detergent lignin CP and measures of lignin, neutral detergent fiber (NDF), and digestibility. Specifically, the study examined whether a relationship existed between these measures and the CP content of feed or the residual CP found in ADF or acid detergent lignin. Sixty-seven samples (15 alfalfa hay, 16 tall fescue hay, 15 orchardgrass hay, 10 vegetative corn plants, and 11 vegetative wheat plants) were collected at different maturities for study. Samples were analyzed for CP, NDF, digestibility, and lignin (acid detergent, permanganate, chlorite, and acetyl bromide). In addition, batches of ADF and acid detergent lignin were prepared for CP determination. Results of correlations between the feed CP, ADF CP, or acid detergent lignin CP and measures of lignin, NDF, or digestibility were found to be highly dependent on feedstuffs. In some instances, such as the correlations between acid detergent lignin CP and lignin, NDF, or digestibility, different feedstuffs produced equally close, but opposite (positive versus negative) correlations for the same relationship. Consideration of the type of material involved, maturity, or the assay was of little help in explaining the results. Overall, CP contamination was a significant problem for the determination of ADF and lignin concentrations.