The paper discusses the problems presented by lignin to animal production, particularly in countries with hot climates, where the degree of lignification in plants is extremely variable causing unpredictable reductions in digestibility. The difficulty of chemically defining lignin compounds is reviewed with the conclusion that a combination of traditional and advanced techniques is required if the biological role of the lignin in the plant is to be explained. Experiments in ruminants have often shown incomplete recovery of compounds traditionally referred to as lignin, leading to the suspicion that a limited digestion of lignin could occur under anaerobic conditions, with fungi playing a predominant role in the process. As is well known, the problem is difficult to study in both aerobic and anaerobic conditions. White-rot fungi - Phanerochaete chrysosporium - has become a standard model for in vitro aerobic digestion. The in situ technique appears to be the most suitable for studies under anaerobic conditions, and some results are presented indicating apparent lignin digestibility in forages.
