Consumption of Tannin-Rich Forage by Ruminants: From Mechanism to Improved Performance

Abstract

Trees and shrubs are potentially important sources of food for livestock in many parts of the world, but their use is limited by tannins. Tannins reduce food intake by decreasing digestibility or by causing illness. Supplementing cattle, sheep, and goats with polyethylene glycol (PEG), which has a high affinity for binding tannins and thus attenuating their aversive effects, increases intake of high-tannin foods and improves weight gains and wool growth. The objectives of this proposal were: Objective 1: To further delineate the conditions under which PEG affects intake of high-tannin foods. Objective 2: To ascertain if animals self-regulate intake of PEG in accord with the tannin content of their diet under pen, paddock, and field conditions. Objective 3: To determine how nutritional status and PEG supplementation affect preference for foods varying in nutrients and tannins. Objective 4: To assess the effects of PEG on food selection, intake, and livestock performance in different production systems. The results from this research show that supplementing livestock with low doses of PEG increases intake of high-tannin foods and improves performance of cattle, sheep, and goats. Neutralizing the effects of tannins with supplemental PEG promotes the use of woody species usually considered useless as forage resources. Supplementing animals with PEG has the potential to improve the profitability - mainly milk production - of high-yielding dairy goats fed high-quality foods and supplemented with browse in Mediterranean areas. However, its contribution to production systems utilizing low-yielding goats is limited. Our findings also support the notion that supplemental PEG enhances the ability of livestock to control shrub encroachment and to maintain firebreaks. However, our work also suggests that the effectiveness of supplemental PEG may be low if alternative forages are equal or superior in nutritional quality and contain fewer metabolites with adverse effects.