The implications of condensed tannins on the nutritive value of temperate forages fed to ruminants

New methodology for measuring forage condensed tannin (CT) content is descr ibed and the effects of CT upon forage feeding and nutritive value for rumi nant animals are reviewed. CT react with forage proteins ina pH-reversible manner, with reactivity determined by the concentration, structure and mole cular mass of the CT. Increasing concentrations of-CT in Lotus corniculatus and Lotus pedunculatus reduce the rates of solubilization and degradation of fraction I leaf protein in the rumen and increase duodenal non-NH3 N flo w. Action of medium concentrations of total CT in Lotus corniculatus (30-40 g/kg DM) increased the absorption of essential amino acids from the small intestine and increased wool growth, milk secretion and reproductive rate i n grazing sheep without affecting voluntary feed intake, thus improving the efficiency of food conversion. High concentrations of CT in Lotus peduncul atus (75-100 g/ kg DM) depressed voluntary feed intake and rumen carbohydra te digestion and depressed rates of body and wool growth in grazing sheep. The minimum concentration of CT to prevent rumen frothy bloat in cattle is defined as 5 g/kg DM and sheep grazing CT-containing legumes were shown to better tolerate internal parasite infections than sheep grazing non CT-cont aining forages. It was concluded that defined concentrations of forage CT c an be used to increase the efficiencies of protein digestion and animal pro ductivity in forage-fed ruminants and to develop more ecologically sustaina ble systems of controlling some diseases under grazing.