Effects of Warm-Season Legume Tannins on Internal Parasites of Livestock.

Infection with gastrointestinal nematodes (GIN) is one of the greatest constraints to sustainable livestock production in tropic and subtropical regions. With rapidly increasing prevalence of anthelmintic-resistant GIN, alternative control therapies are critically needed. Tannins in tropical/subtropical plants represent a largely untapped resource for natural control of internal parasites and pests in both small and large ruminants. While condensed tannins (CT) and other compounds in a number of different tropical/subtropical plants have shown anti-parasitic properties against different life stages of GIN (eggs, larvae, adults) and other internal parasites, including Eimeria spp. (coccidia), there are a number of different factors that influence the bioactivity of these compounds as well as the nutritive value of these forage/browse plant resources. These include CT concentration, chemical structure, size (molecular weight) and solubility (bound or unbound) in different plant species, how the plant is utilized in forage-livestock systems (grazed/browsed directly, sun-dried as hay, processed as leaf meal or pellets, preserved as silage), the target parasite species or life stage, and the host species. Agronomic and nutritional properties of CT-containing tropical/subtropical fodder plants also interact with these factors to influence anti-parasitic bioactivity of CT and the use of these plant resources in forage-livestock systems. Activities of CT in ruminant systems have been identified prior to ingestion, within the rumen, during passage through the intestines, as well as in fecal material. The growing body of evidence from in vitro and in vivo studies indicates that CT in tropical/subtropical forage/browse plants, or CT extracted from these plant resources have excellent potential for use in integrated, sustainable parasite and pest control systems with domesticated and wild ruminant species.