Forage Condensed Tannins Have a Role in Integrated Pest Management.

Condensed tannins (CT) are polyphenolic compounds found in forage legumes that serve as defense against herbivory via constitutive resistance (e.g. acting as a poison to herbivores) or induced resistances (e.g. affecting ground litter after leaf senescence). They bind to compounds including starch, cellulose, proteins and minerals and influence feed intake and efficiency, growth rate, and protein digestibility. A series of studies suggests that manure samples from dairy cattle laced with CT from forage legumes had a negative effect on house fly (Musca domestica) development.  Condensed tannins, either fed through the animals or added directly to manure, reduced (P≤0.05) the number (23% reduction reared in 3 and 5% CT from PTC-fed dairy cattle manure) and weight (60% reduction with the addition of PTC and quebracho at 3 and 5% and 37% for flies in SL-fed goat manure) of emerging adult house flies. Studies confirmed that CT were at play by achieving the same results from introducing purified catechin (1 or 3% of dairy manure). Inexplicably, CT in goat manure was less effective than in dairy manure, despite equilibrating for moisture content. Not all legume CT produce the same effects, indicating that not all are equal when it comes to fly suppression. In addition, concentration of CT makes a difference.   Subsequent studies to determine how CT had these effects indicated that CT may affect fly development by negatively impacting microbial activity, the latter important in breaking down nutrients in the manure to feed fly larvae.  This last finding indicates that forage CT may have additional microbial applications in livestock herds beyond house fly suppression. Forage species can be selected based on CT concentrations and characteristics to suit the needs of a specific operation. Future research to genetically modify legume species to produce CT is warranted. These legumes can be used to improve ruminant health and nutrition through the provision of rumen bypass protein, reduction of bloat, suppression of internal parasites or house flies and mitigation of fecal microbial activities.