Feeding Behavior in Chicks Fed Tea Saponin and Quinine Sulfate

Tea saponin is known to depress growth rates of chicks by decreasing feed intake. Since tea saponin has bitter taste, gustatory sensation was proposed to be responsible for the decreased feed intake. However, inconsistent observations are also reported. The present experiment was conducted with chicks to evaluate the involvement of factors other than taste in the decreased feed intake due to saponin. Chicks freely fed diets containing tea saponin or quinine sulfate at 0.5 and 1% levels for 12 h decreased feed intake within 4 h. Chicks given a choice between the basal diet and the diet containing 0.5 or 1% quinine sulfate for 12 h showed strong aversion to quinine-added diets within 4 h. Chicks preferred the basal diet to the diet containing 0.5 or 1% saponin in a similar two-choice preference test, but there were no statistical differences in feed intake of the first 4 h between the basal diet and the diet containing 0.5% saponin. When chicks were given a free access to the basal diet for 6 h a day in a 12-d feeding experiment, daily feed intake during 0-2 h was kept constant, whereas feed intake during 2-6 h gradually increased as the experiment progressed. On the other hand, feed intake during 0-2 and 2-6 h in chicks fed the diet containing 0.5% saponin was always suppressed to the same extent throughout the experiment. Force-feeding this saponin-added diet delayed the crop emptying, which was reversed by the concomitant addition of cholesterol. These results suggest that the decreased feed intake due to tea saponin is related to the crop distention by the ingesta remained in this organ rather than taste.