Effect of heat and several additives related to stress levels on fluctuating asymmetry, heterophil: lymphocyte ratio, and tonic immobility duration in White Leghorn chicks

The purpose of this study was to analyze the effects of heat and several additives related to stress on fluctuating asymmetry (groups 1 to 10), heterophil: lymphocyte ratio (groups 1 to 3 and 8 to 10), and tonic immobility duration (groups 1 to 7 and 10) in White Leghorn chicks at 42 d of age. Chicks in group 1 (heat) were reared with temperatures 8 degrees C greater than those of the control group. Groups 2 to 9 consisted of chicks reared with temperatures 8 degrees C greater than those of the control group and addition of capsaicin, allicin, ascorbic acid, tryptophan, brewer's yeast, lactic acid, corticosterone, or cholesterol in diet. Chicks in group 10 (control) were reared with standard temperatures. Heat effect was significant (P < 0.05) for the heterophil: lymphocyte ratio, which was greater in heat-stressed chicks without any additives and smaller in control chicks. There were no significant differences for the fluctuating asymmetry and the tonic immobility duration between both groups. Heterophil: lymphocyte ratio for heat-stressed chicks with capsaicin or allicin was significantly lower (P < 0.05) than that of heat-stressed chicks without any additives. Capsaicin effect was not significant for the fluctuating asymmetry and the tonic immobility duration, whereas allicin significantly increased fluctuating asymmetry of wing length and tonic immobility duration (P < 0.05). The addition of lactic acid or corticosterone resulted in greater fluctuating asymmetry of wing length of heat-stressed chicks (P < 0.05). In conclusion, an increased heterophil: lymphocyte ratio was found in heat-stressed chicks without additives, indicating that it is a more reliable indicator of the effect of heat in chicks. In addition, dietary capsaicin or allicin supplementation was effective to alleviate the stress induced by the high temperature, as indicated by a lower heterophil: lymphocyte ratio.