Aversion to Quinine is Associated with Taste Sensation in Chicks

Abstract

Quinine is known as a bitter compound for humans and also used in animal experiment. However, there is no evidence that animals share the same taste sensation of quinine with humans. The purpose of this experiment was to elucidate how chicks perceive quinine. First, 14-d-old chicks were freely fed diets varying in quinine HCl (0, 0.2, and 0.8%) for 3 or 4 d as a single diet, or given a choice between the quinine-free basal diet and a diet containing 0.2% quinine HCl for 4 d. Feed intake of quinine added diets depressed within the first 4 h after the start of the experiment, after which it increased with time. Especially, chicks became accustomed to 0.2% quinine HCl from the second d of the experiment. As contrasted with this result, choice-fed chicks did not differentiate between the basal diet and the diet containing 0.2% quinine HCl during the first 4 h, after which they had the aversion to the quinine-added diet over 4 d. Chicks fed 0.4% quinine HCl increased water intake as compared with those fed the basal diet, irrespective of the lower body weight and feed intake. Next, chicks previously fed diets containing 0,0.2 or 0.8% quinine HCl were given a choice between the basal diet and the diet containing 0.2% quinine HCl for 24 h. Chicks previously fed 0.2% quinine HCl was more sensitive to the dietary quinine than those fed the basal diet previously, but chicks fed 0.8% quinine HCl for 4 d did not discriminate between the two diets. The adverse effect of quinine was not carried over, because chicks previously given the quinine-added diets ate more diet than those previously fed the basal diet immediately after the start of the experiment when they were offered a chance to eat the basal diet in the choice feeding. These results indicated that the aversive effect of quinine on chicks was associated with the uncomfortable taste sensation as humans perceived.