Tea saponin is known to suppress chick growth rate by decreasing feed intake, although the mechanism by which tea saponin decreases feed intake remains obscure. Since tea saponin has bitter taste, palatability was suggested to be a major factor affecting feed intake. However, there are some experimental results showing another possibility. The present experiment was conducted with chicks to evaluate the involvement of taste in the adverse effect of tea saponin on feed intake. When Single Comb White Leghorn male chicks were given a casein diet for at least 4h in experiments 1 and 2, 1% tea saponin depressed feed intake. The decrease in feed intake immediately after feeding (0-2h) was rather mild and became severer with time (2-4h). Removal of saponin from the diet increased feed intake, and this beneficial effect was manifested for the 2-4h of the feeding period as compared with the first 2h. In experiment 3, 40mg of tea saponin was administered directly to the proventriculus by capsules to avoid the effect of taste or orally as a 1% solution. Despite the fact that chicks were given free access to the saponin-free diet after the administration, the depression in feed intake due to saponin was lasted until 8h had passed, irrespective of different dosing methods. These results show that the aversion to the saponin-added diet does not occur immediately after the ingestion of tea saponin and that the adverse effect of tea saponin on feed intake is carried over. Thus, it seems unlikely that taste is a primary factor decreasing feed intake in chicks given tea saponin.
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