Purified lignin: Nutritional and health impacts on farm animals—A review

Lignin, the second most abundant natural compound after cellulose (Boudet and Grima-Pettenati, 1996), is a high-molecular weight polymer of phenolic compounds that occurs naturally in plants. It is mostly present in the cell wall, conferring structural support, impermeability and resistance to microbial attack. Commercial purified lignin is produced as a by-product of the paper industry, separated from wood by chemical pulping processes. These purified lignins are low molecular weight mono-phenolic fragments that have biological characteristics that differ from those of native lignin. Different chemical treatments during wood-pulping processes yield diverse types of purified lignin, such as Alcell lignin and Kraft lignin. Although these phenolic fragments may potentially have important applications in animal agriculture, research with purified lignin has not received much attention and there are few published results. In contrast to native lignin, purified lignin does not represent a barrier to digestion in monogastric or ruminant animals. Several in vitro and in vivo studies have demonstrated antimicrobial properties of the phenolic fragments in purified lignin. Recently, purified Alcell lignin has been shown to exhibit prebiotic effects in chickens, favouring growth of beneficial bacteria and improving the morphological structures of the intestines, as measured by increased villi height and goblet cell number. These findings suggest that purified lignin may exert health benefits in monogastric animals and could potentially be considered as a natural feed additive. Based on the few published studies, animal responses to purified lignin seem dependent on dosage, animal species and type and source of the lignin product. More research is required before establishing conclusive benefits of purified lignin on animal performance and health.