Utility of the browser's behavioural and physiological strategies in coping with dietary tannins: Are exogenous tannin-inactivating treatments necessary?

The desire to reduce feeding costs in small-ruminant production systems has led to increased reliance on non-conventional locally available browse products as protein supplements. Browse products contain variable quantities of tannins, whose nutritional effects on the animal can be positive or negative. Because of the lack of rapid evaluation techniques and methods that can differentiate, accurately, between potentially beneficial and harmful tannins, most researchers employ a 'safety first' approach in which tannin-inactivating treatments are applied to browse products to protect the animal and enhance feed utilization. This is despite the fact that browsing herbivores are known to have various behavioural and physiological strategies to cope with a number of anti-nutritional plant compounds, which include tannins. In this paper, the authors explore the rationale behind recommending the use of tannin-neutralization strategies when feeding animals with browse leaves and fruits. Are browsing herbivores' own coping strategies sufficient to protect them from suboptimal nutrition and possible toxicity caused by tannins or is intervention always required? In an attempt to answer this question, this review presents the current state of knowledge of tannins in ruminant nutrition before summarizing the strategies that browsing herbivores use to cope with tannins and their potential utility in various rearing systems. Finally, the utility of exogenous tannin inactivation strategies and the animals' own coping strategies are compared. Feeding scenarios are identified in which exogenous inactivation strategies may be worthwhile.