Lignin in Fibrous Feed as an Internal Digestibility and Transit Marker in Pigs

To assess the nutritional value of fibrous diets, external metal oxide-based markers are commonly used. Given the increasing restrictions on the use of these conventional markers, we investigated the inertness of lignin in pigs and correspondingly its potential as an internal marker. Hereto, feces and digesta were collected from pigs fed a diet containing wheat straw as sole lignin source, and lignin was quantified by ¹³C-IS py-GC-MS. Combined with detailed HSQC NMR and size-exclusion chromatography structural analysis, we revealed that lignin was recovered unmodified in feces. Comparison of lignin with TiO₂ showed similar (<i>P</i> > 0.15) digestibility values for nitrogen (82.6 vs 80.2%) and fat (93.3 vs 92.5%), and a limited difference for dry matter (77.7 vs 74.1%, <i>P</i> = 0.01). Comparison of lignin with chromium-mordanted straw furthermore showed highly similar (<i>P</i> = 0.8) mean retention times of fibrous particles in the stomach. We thus confirm the potential of intrinsic lignin as a multifunctional marker for feed digestibility and digesta transit in pigs.