The Effect of In Ovo Administration of Rosemary Essential Oil on Hatchability, Relative Hatching Weight, and Embryo Mortality Rate in Japanese Quail (Coturnix coturnix japonica)

SIMPLE SUMMARY: In poultry, supplementing diets with essential oils has gained much interest. It has been established that supplementing avian diets and water with rosemary essential oil improves growth performance. Furthermore, although it is known that the nutritional status of the egg is sufficient to ensure embryo development until hatching, growth performance during and after hatching is further enhanced by in ovo supply of neonatal exogenous nutrients. The in ovo technique consists of injecting exogenous substances inside hatching eggs to improve embryonic development, hatching, and post-hatch parameters. To the best of our knowledge, few studies have explored the effect of in ovo injection of essential oils. The objective of this study was to explore the effects of in ovo injection of different concentrations of rosemary essential oil on embryonic development and hatching parameters in Japanese quail. The findings indicated that the in ovo injection of rosemary essential oil at a low concentration (1 µL/egg) was beneficial for improving hatching compared to 3 µL/egg, which proved to be toxic to the quail embryo. However, it should be noted that both treatments increased the relative weight of chicks at hatching compared to control groups. ABSTRACT: This study aimed to determine the effects of air sac injection of rosemary essential oil at different concentrations in ovo in quail eggs on hatching rate, relative chick weight at hatching, and embryonic mortality rate. A total of 1060 Japanese quail eggs were divided into four groups: negative control (non-injected), positive control (30 µL sterile distilled water/egg), and two treated groups with 1 and 3 µL oil/egg, respectively. The concentration of 3 µL/egg showed a toxic effect on embryonic development, as revealed by the significantly (p = 0.015) higher post-injection mortality rate (18.21%) compared to 1 µL/egg with 8.3%. Furthermore, hatchability was significantly increased (p = 0.0001) with 1 µL/egg compared to 3 µL/egg with 69.1% and 44.48%, respectively. No significant difference was observed between the concentration of 1 µL/egg and the control groups (p = 0.822). Both l and 3 µL essential oil/egg significantly enhanced (p = 0.0001) relative chick weight at hatching by 67.14% and 70.32%, respectively, compared to the control groups. In conclusion, injecting eggs with 1 µL oil/egg showed positive effects both on hatching and relative chick weight. The concentration of 3 µL/egg was revealed to be toxic, with dramatic effects on embryonic survival.