EFFECT OF CONDENSED TANNINS IN LOTUS-CORNICULATUS UPON THE DIGESTION OF METHIONINE AND CYSTEINE IN THE SMALL-INTESTINE OF SHEEP

An experiment was conducted at Palmerston North, New Zealand, to deter mine the effect of condensed tannins (CT) on the true and apparent dig estion of methionine and cysteine in the small intestine (SI) of sheep fed fresh Lotus corniculatus. The lotus contained c. 30 g total CT/kg dry matter (DM) and was fed hourly to sheep in metabolism crates. Fou r sheep were prepared with rumen and abomasal cannulae which enabled t he indigestible liquid phase marker, chromium ethylene diamine tetra-a cetic acid (Cr-EDTA), to be infused into the rumen to estimate digesta flow. True digestibility of plant methionine and cysteine in the SI a nd their site of absorption in the SI were determined from S-35-labell ed L. corniculatus homogenate continuously infused into the abomasum. After 9 h infusion of the S-35-labelled lotus homogenate, the sheep we re slaughtered and digesta samples were taken at intervals along the s mall and large intestines. The effect of CT was determined by comparin g two control sheep (CT-acting) with two sheep given a continuous intr aruminal infusion of polyethylene glycol (PEG, MW 3500) to bind and in activate the CT. The CT reduced the true digestibility of plant methio nine (0.72 v. 0.88) and cysteine (0.65 v. 0.81) in the SI relative to sheep receiving PEG. Condensed tannins also appeared to alter the site of digestion of both [S-35]methionine and [S-35]cysteine in the SI, a nd increased the flux of both amino acids in the mid and latter thirds of the SI. CT did not affect the apparent digestibility of total meth ionine (0.82 v. 0.84) in the SI but reduced the apparent digestibility of total cysteine from 0.77 to 0.66. In control sheep CT increased th e abomasal flux (as a proportion of eaten) of total digesta methionine (0.88 v. 0.76) and total digesta cysteine (0.74 v. 0.62). The apparen t absorption of total methionine (plant + microbial + endogenous) was increased by the action of CT (0.72 v. 0.63 g/g eaten) but was similar for total cysteine (0.49 v. 0.48 g/g eaten) in both groups. It was co ncluded that CT reduced the true digestibility of plant methionine and cysteine in the SI. However, it was calculated that the action of CT actually increased the total amounts (g/g eaten) of plant methionine a nd cysteine absorbed from the SI, due to its effect in increasing abom asal flux.