EFFECT OF CONDENSED TANNIN IN COTTONSEED HULLS ON ENDOGENOUS ILEAL AMINO-ACID LOSS IN THE GROWING RAT

The effect of condensed tannin (CT) in cottonseed hulls (CSH) on endog enous ileal amino acid flow in the growing rat was evaluated. CSH cont ain around 900 g kg(-1) fibre and 52 g kg(-1) total CT. Twenty-four ra ts were allocated to four semi-synthetic diets, which contained enzymi cally hydrolysed casein (EHC) as the sole source of dietary nitrogen a nd chromic oxide as an indigestible marker. Two of the diets contained no CSH while the remaining two contained 50 g kg(-1) CSH. At each lev el of hull inclusion (0 and 50 g kg(-1)), polyethylene glycol (PEG; MW 3500) was added (6 g kg(-1)) to one of the diets. The effect of CT wa s assessed by determining endogenous ileal amino acid loss in the pres ence or absence of PEG, which binds and inactivates CT. The rats were given their respective experimental diets ad libitum for 14 days. Samp les of digesta were collected at slaughter from the terminal 15 cm of ileum. The digesta samples were centrifuged and the supernate ultrafil tered. The precipitate plus retentate (MW > 10 000) fraction affords a n estimate of endogenous loss. Inclusion of CSH in the EHC based diet increased ileal flow of total nitrogen (1387 versus 1623 mu g g(-1) dr y matter intake; P less than or equal to 0.05), increased ileal flow o f total amino acids (23%; P less than or equal to 0.01), and significa ntly increased ileal flow of several individual amino acids. There was no significant effect of PEG and no PEG x diet interaction, showing t hat the CSH effects could not be explained by action of CT. The presen ce of hulls in commercial cottonseed meal would appear to contribute t o the reported low apparent ileal amino acid digestibility coefficient s for cottonseed meal by increasing endogenous ileal amino acid flow, but this effect is not due to the CT component of the hulls.