Effects of in ovo feeding of arginine, tryptophan, and threonine on hatch performance, hatchability, and morphometry of broiler chickens

The objective of this experiment was to investigate the effects of <italic>in ovo</italic> feeding of arginine (Arg), tryptophan (Trp), and threonine (Thr) on hatch performance, hatchability, and morphometry of newly hatched broiler chickens. A total of 400 fertile eggs from 28-week-old Arbor Acres broiler breeder flocks, with an average fertile egg weight of 52 ± 0.7 g, were collected for the experiment. The eggs were randomly assigned to five treatment groups (80 eggs per group, eight replicates of 10 eggs each): non-injected control (CON); phosphate-buffered saline (PBS) injection (100 μL of 1% PBS); Arg injection (100 μL/egg); Trp injection (100 μL/egg); and Thr injection (100 μL/egg). All eggs were incubated at the recommended temperature and humidity of 38.0 ± 0.2°C and 75.0 ± 3%, respectively. After hatching, one 1-day-old broiler chick per replicate with a body weight (BW) close to the average of each treatment was selected for hatchability and morphometry assessments. Results indicated that CON and PBS groups had significantly greater (<italic>p </italic>&lt; 0.05) BW than Trp and Thr groups. The hatch window was greater (<italic>p </italic>&lt; 0.05) in Thr group compared to CON, PBS, and Trp groups. However, no significant differences were observed among treatments for hatchability such as hatch of set and fertile, egg weight, survival rate, and chick yield. Morphometric analysis revealed that Arg, Trp, and Thr treatment groups exhibited significantly greater (<italic>p </italic>&lt; 0.05) middle toe length compared to CON group. Conversely, small intestine length and chick body length were reduced (<italic>p </italic>&lt; 0.05) in Arg, Trp, and Thr groups compared to CON group. No significant differences were observed in tibia and radius among groups. In conclusion, <italic>in ovo</italic> feeding Arg, Trp, and Thr influenced chick morphology and organ development, indicating that precise dosage optimization of amino acid injection during the embryonic stage is essential.