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1.Of the nineteen plants screened, six were found to contain large quantities of condensed tannins. Black locust (Robinia pseudo-dcucia), bush clover (Lespedezu bicolor), wistaria (Wistaria floribundu) and Japanese knotgrass (Reynoutria juponicu) were used for the present experiment. Tannins of the investigated plants were fractionated into three or four molecular forms, according to the degree of polymerization, by chromatography on a column of Sephadex LH-20.2. The protein-precipitating capacity of the fractionated tannins increased with the increase in degree of polymerization. The inhibitory effect of tannins on trypsin (EC 3 . 4 . 2 1 .4), a-amylase (EC 3 . 2 . 1 . 1) and lipase (EC 3 . 1 . 1 .3) activities in vitro also increased with the increase in degree of polymerization. The digestion of tannin-bovine serum albumin complex by trypsin was related to the degree of polymerization of tannins complexed.3. Inclusion of black locust tannins in the diet (10 g/kg) depressed the activities of trypsin and a-amylase in the upper, middle and lower parts of the intestine of the rats, but the lipase activity was increased in the middle part and remained unaffected in the upper and lower parts. It is presumed that the tannins have little affinity for lipase. Barry (1985) reported also that the liveweight gain and voluntary intake were low for sheep grazing high-tannin forage. Tannins are classified into hydrolysable and condensed types and the inhibitory effect on trypsin activity is more marked with condensed tannins than with hydrolysable tannins (Tamir & Alumot, 1969). It is also suggested that the principal tannins found in forage leaves are of the proanthocyanidin type formed by the polymerization of flavan-3,4-diols either alone or in combination with other flavonoids such as catechins (McLleod, 1974;Jones et al. 1976). 4.The present work was undertaken to isolate tannins from the leaves of black locust (Robinia pseudo-Acacia), bush clover (Lespedeza bicolor), wistaria ( WistariaJEoribunda) and Japanese knotgrass (Reynoutria juponica) which were found to have proanthocyanidin-type tannins in a survey of tannin-containing plants, and to investigate the effect of isolated tannins on trypsin (EC 3 . 4 . 2 1 .4), a-amylase (EC 3 . 2 . 1 . 1) and lipase (EC 3 . 1 . I .3) in vitro and in the intestine of rats. EXPERIMENTAL Survey of the plants containing condensed tanninsAnthocyanidin-formation and protein-precipitation tests were used for the survey of condensed tannin-containing plants.

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Plants rich in secondary metabolites (saponins, tannins, essential oils, etc.) have antimicrobial activity which can be exploited for selective inhibition of a particular group of microbes in the rumen. We have screened a large number of plant extracts for their potential to inhibit methanogenesis and ciliate protozoa in an in vitro gas production test using buffalo rumen liquor as the inoculum. Out of 93 plant extracts tested, 11 inhibited in vitro methanogenesis to the extent of 25-50% and nine plant extracts inhibited methanogenesis more than 50%. Among 20 extracts exhibiting antimethanogenic activity, nine were ethanol extracts, 10 were methanol extracts and only one was a water extract. Some of these plant extracts inhibited ciliate protozoa as tested by microscopic examination and 14 C-labelled radioisotopic technique, but the protozoa inhibition was not correlated with methane inhibition, indicating that the methanogens sensitive to plant secondary metabolites may or may not be having any symbiotic relationship with ciliate protozoa. Methane inhibition was accompanied by a drastic fall in the number of methanogens as determined by real time PCR. Plants that appeared to have some potential as feed additives to control methanogenesis by the ruminants are: (i) seed pulp of Sapindus mukorossi (rich in saponins) and Terminalia chebula (rich in tannins); (ii) leaves of Populus deltoides, Mangifera indica and Psidium guajava (rich in tannins and essential oils); and (iii) flower buds of Syzygium aromaticum and bulb of Allium sativum (rich in essential oils). Some of the plants reported in literature exhibiting antimethanogenic activity include