A total of 540 Japanese quail eggs were in ovo-injected at day 11 of embryonic development to evaluate the effects of in ovo feeding of threonine (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 that received in ovo injections of 0.05 or 0.1 mL of saline with or without THR (5 mg/ml). All injections were administered in (IAS) or under (UAS) the air sac. Hatchlings from all treatments [except the 0.05 mL THR UAS group (5TUAS)] received a corn-soybean meal basal diet until 10 days of age. Birds from the 5TUAS group were divided into three post-hatch groups: 1) Control diet [corn-soybean meal basal diet based on NRC (1994) recommendations]; 2) Control diet + 10% higher THR than NRC; 3) Control diet + 20% higher THR than NRC. The hatchability of eggs from the 5TUAS and 0.05 mL saline UAS groups were not different from the control, although hatchability was higher in those 2 groups in comparison to that with other supplemental treatments. Interestingly, the 5TUAS group had the highest jejunum villus height and surface area, villus height/crypt depth ratio, and goblet cell numbers in comparison to the other treatments. The BW of 5TUAS chicks was lower than that of all the other treatments on d 13 of incubation and on the hatch day. However, 5TUAS chicks had a higher BW at 10d post-hatch. Thus, an in ovo 5TUAS treatment may improve the intestinal morphology and day 10 post-hatch BW of Japanese quail. Further investigations are needed to verify the applicability of new feeding approaches administered by in ovo injection.

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