Klason lignin is a nutritionally heterogeneous fraction unsuitable for the prediction of forage neutral-detergent fibre digestibility in ruminants.

Although lignin has been negatively correlated with neutral-detergent fibre (NDF) digestibility (NDFD) in ruminants and used to predict potential extent of NDF digestion of forages, selection of an analysis, Klason lignin (KL) or acid-detergent lignin (ADL), to describe that the nutritionally relevant lignin has not been resolved. Dismissed as an artifact is the difference between KL and ADL (ΔL). A question is whether ΔL influences NDFD. We evaluated the relationships of ΔL, KL and ADL with NDFD in order to determine the nutritionally homogeneous or heterogeneous nature of KL. Data sets from two laboratories (DS1 and DS2) were used that included ADL, KL and in vitro NDFD at 48 h (NDFD48). DS1 contained seven C3 grasses, seventeen C4 maize forages and nineteen alfalfas, and DS2 had fifteen C3 grasses, eight C4 forages and six alfalfas. Mean ΔL was greater than ADL in C3 and C4 samples and less in alfalfas. Within forage type and laboratory, ΔL was not correlated with NDFD48 (r -0·34-0·49; all P > 0·17). ADL was more consistently correlated with NDFD48 (r -0·47--0·95; P < 0·01-0·21) than with KL (r 0·03--0·91; P < 0·01-0·94). ΔL as a proportion of KL was correlated with NDFD48 in C3 and C4 samples (r 0·44-0·76; P < 0·01-0·08). The differing behaviours of ΔL and ADL relative to NDFD48 indicate that KL is a nutritionally heterogeneous fraction, the behaviour of which may vary by forage type and ratios of ADL and ΔL present.