The effects of dietary essential oil mixture supplementation preserved by two different methods on performance and some blood parameters of laying quails under chronic noise exposure

This study was conducted to determine the effects of essential oil mixture (orange peel oil + bay leaf oil + thyme oil) added into basic mixed feed on performance parameters, egg quality, some blood parameters, antioxidant parameters, and digestion degree of nutrients in laying quails (Coturnix coturnix Japonica) exposed to chronic noise. Totally 100 laying quails, including 25 animals in each group, were used in the study. Every group was divided into 5 subgroups including 5 laying quails in each one. The animals were exposed to 100 dB of noise for 8 hours daily for 56 days. The study groups were as follows; the group Negative Control (NK) for which only zeolite was added into mixed feed without exposure to noise, the group Positive Control (PK) for which only zeolite was added into mixed feed with exposure to noise, the group Zeolite which was exposed to noise and received the mixed feed added with zeolite and 400 ppm dose of stabilized essential oil mixture, and the group Capsule which was exposed to noise and received the mixed feed added with 400 ppm dose of stabilized essential oil mixture by microcapsulation. It was determined that there was no statistical difference among the groups in terms of live weight, egg weight, and feed consumption (P>0.05); however, the highest feed conversion ratio (P<0.001) and the highest egg yield (P<0.01) were in capsule group. Albumen height (P<0.001), albumen length (P<0.001), and Haugh unit (P<0.01) from egg quality criteria were found to be statistically higher in groups receiving feed with essential oil mixture than control groups; weight of shell (P<0.01), on the other hand, was lower. While the minimum egg width and yolk height were determined in group zeolite (P<0.001), the minimum shell ratio was detected in positive control group (P<0.01). While the study revealed a statistical difference between negative control and positive control groups and zeolite groups in terms of glucose level (P<0.05), glucose and cholesterol levels elevating with the effect of stress slightly decreased in capsule group. Negative control group was statistically different from positive control group in terms of cholesterol level (P<0.05), cholesterol level elevated by the effect of noise stress decreased in groups receiving essential oil added feed. While essential oil mixture had a positive influence on triglyceride level, triglyceride level was lower in these groups compared to control groups (P<0.05). Neither noise stress nor the used essential oil had any effect on total protein level (P>0.05). While the minimum values for digestion degrees of dry matter (P<0.05) and ether extract (P<0.001) in mixed feed were determined in positive control group, digestion degree of crude protein was higher in groups fed with essential oil added feed than control groups (P<0.01). Although there was a difference between negative control and positive control groups in terms of plasma malondialdehyde (MDA) level (P<0.05), no difference occurred between groups of essential oil added feed and both control groups. Capsule group had the highest plasma catalase level (P<0.05). The lowest MDA level of liver was determined in negative control group (P<0.05), capsule group was statistically similar to negative control group. A statistical difference was determined between capsule group and negative control group in terms of glutathione (GSH), glutathione peroxidase (GSH-Px), and catalase enzyme levels of liver (P<0.05). MDA levels of heart were different between negative control group and capsule group and between positive control group and zeolite group (P<0.01). Capsule group had the highest catalase level (P<0.05). The study did not reveal a statistical difference among the groups in terms of mortality rate (P>0.05). In conclusion, essential oils used due to their antioxidant characteristics were identified to decrease negative effects of noise stress. However, it was concluded that further studies are needed about the efficiency of microcapsulation method to be used for stability of essential oils.