1. Two experiments were conducted to determine the effects of tannins on nu
trient utilisation in the White Pekin duck.
2. Experiment 1 was a rapid nutrient balance assay to determine the nitroge
n (N) retention and metabolisable energy (ME) of maize, low-tannin sorghum
(P-954063) (Sorghum bicolor (L). Moench) and high-tannin sorghum (IS-4225)
cultivars for ducks. The assay lasted 120 h, with an initial 24 h food-depr
ivation period, a 48 h excreta collection period for endogenous losses and
a 48 h excreta collection period for ingredient losses. The true metabolisa
ble energy (TMEn) content was lower (P < 0.05) in the high-tannin sorghum c
ultivar (13.85 MJ/kg) than the maize (14.94 MJ/kg) and the low-tannin sorgh
um cultivar (14.39 MJ/kg). True N retention was lower (P < 0.05) for the hi
gh-tannin sorghum (0.24 g) than for maize (1.33 g) and low-tannin sorghum (
1.31 g).
3. In experiment 2, the brush-border membrane vesicles technique was used t
o determine whether tannic acid caused inhibition of L-threonine transport
across duck intestinal brush-border membrane. The brush-border membrane ves
icles were mixed with tannic acid solutions (pH 7.4) to give gradient tanni
c acid concentrations of 0, 0.05, 0.10, 0.25, 0.50, 1.00 and 2.50%. As a fr
action of the control (no tannic acid), the maximal inhibition of L-threoni
ne transport (I-max) under the sodium-gradient condition was 77.10% (P < 0.
05). Under the sodium-free condition, the maximal inhibition of L-threonine
transport (I-max) was 45.15% (P < 0.05).
4. These results demonstrated that nutrient utilisation in the White Pekin
duck was lower from the high-tannin sorghum cultivar than from the low-tann
in sorghum cultivar. The results also suggested that the antinutritive effe
cts of tannins in foodstuffs are due partly to their inhibitory action on i
ntestinal brush-border bound amino acid transporter proteins.