Growth Response and Crop Emptying in Chicks Force-Fed Diets Containing Various Saponins

Some kinds of saponins are considered to depress body weight gain in chicks by reducing feed intake. Although the mechanism by which saponins exert such effects is unclear, tea saponin (TS) is known to delay the crop emptying. The purpose of the present experiment was to compare effects of TS, Quillaja saponin (QS) and Yucca saponin (YS) on growth rate and crop emptying using force-fed chicks. Chicks fed ad libitum a diet containing 0.5% TS, 0.5% QS or 2% YS depressed body weight gain and feed intake in a 7-d experiment. These adverse effects were alleviated by the concomitant addition of cholesterol. The growth retardation did not occur when feed intake of the diet containing 0.5% QS or 2% YS for 10d was equalized to that of the basal diet by force-feeding. On the other hand, it was difficult to continue the force-feeding of the diet containing 1% TS more than 3d because of the severe crop distention due to the ingesta. YS at the 2% in the diet also delayed the crop emptying, extent of which was milder than 1% TS. The concomitant addition of cholesterol alleviated the delayed crop emptying due to TS or YS. Force-feeding the diet containing 1% QS had little effect on the crop emptying, although the adverse effect of QS on feed intake was similar to that of TS or greater than that of YS. On the other hand, half of chicks force-fed the diet containing 1% QS died within 24-36h after feeding. These results indicate that the decreased feed intake plays an important role in the growth retardation due to saponins, and they also suggest that the delayed crop emptying is associated with the decrease in feed intake due to some saponins but not to all saponins.