ABSTRACTA total of 540 Japanese quail eggs were in ovo injected threonine (THR) at day 11 of embryonic development to evaluate the effects of in ovo feeding of THR on the hatchability, somatic attributes, and gut morphology of hatchlings. A completely randomized experimental design with 9 treatments and 4 replicates of 15 eggs per replicate was used. The treatments were non-injected (control) eggs and those receiving in ovo injections of 0.05 or 0.1 ml of saline (diluent) with or without THR (5 mg/ml) in the air sac (IAS) or under the air sac (UAS). Although the number of hatched eggs injected with 0.05 ml diluent both with and without THR under the air sac was not significant in comparison to the control group, it was higher than that of the other injected treatments. Interestingly, the under air sac injection of 0.05 ml THR showed enhanced gut morphology in comparison with the other treatments. The dried yolk-free body weight of all chicks was not statistically significant. Overall, the present results suggest that the injection of 0.05 ml THR under the air sac may improve the intestinal morphology in newly hatched quail while having no negative effects on final yolk-free body weight.