Methionine is an essential amino acid crucial in developing feathers and protein synthesis and plays a role in the growth and production performance of poultry. The main objective of the study was to evaluate the physiological responses of newly hatched chicks to in-ovo supplementation of DL-Met and L-Met in TETRA-SL LL hybrid (TSL) and Hungarian partridge colored hen breed (HPC) layer genotypes. Additionally, this study aimed to assess the effects of dietary supplementation with DL-Met and L-Met on the growth performance and hematological parameters of TSL chicks during the starter phase. Two experiments were performed to investigate the effect of DL and L-Methionine at different supplementation levels on the physiological responses, performance, and feather development of layer genotypes. The first experiment examined the impact of in-ovo feeding of methionine sources at 5, 10 and 15 mg/egg on chick development, health status, and hatching performance of the two genotypes. The results indicated that the hatchability ranged from 72% to 100% of 5 mg supplementation; while the in-ovo feeding of higher methionine doses resulted in considerable lower hatchability. However, the in-ovo feeding of DL-methionine significantly improved the hatching weight and ferric-reducing ability of the plasma (FRAP) compared to L-methionine (P < 0.05). Both methionine sources enhanced the chicks' liver health and antioxidant status. Moreover, the in-ovo feeding of either DL-methionine or L-methionine improved intestinal development by increasing the villus width, height, and surface area compared to the control in both genotypes (P < 0.05). The genotype responses to the in-ovo feeding of methionine sources were also noted; the TSL genotype had improved hatching weight, heart weight, hepatic GSH, total antioxidant capacity (TAC), and FRAP than the HPC genotype (P < 0.05). While the HPC genotype had significantly higher muscle GSH and TAC levels, upregulated hepatic IGF1 and IGF1R receptors than the TSL genotype (P < 0.05). The HPC genotype also had overexpressed intestinal IGF1, tricellulin (MD2), OCLN, and superoxide dismutase 1 (SOD1) and GST3 genes than the TSL genotype (P < 0.05). The second experiment used 96-day-old TETRA SL (TSL) chicks and found no significant effect of methionine sources and levels on body weight, average daily gain, and feather development up to 28 days (P > 0.05). However, methionine source and levels had a significant effect on body weight and average daily gain on day 28 (P < 0.05). Furthermore, both methionine sources and levels significantly influenced the hematological parameters, including red blood cells, haemoglobin, white blood cells, lymphocytes, mid-range, and granulocytes values (P < 0.05). The dietary supplementation of DL-methionine at 100% of the recommendation showed favorable results with the highest WBC, RBC, Hb, and Ht values than all treatment groups (P < 0.05). In conclusion, the study highlights the importance of genotype-specific gene expression patterns for enhancing poultry productivity and health. In ovo feeding, L-Met was found to be more effective than DL-Met and was effectively utilized in Hungarian Partridge Colored chicks for muscle GSH, increased intestinal NRF2 gene expression, and decreased plasma uric acid content. On the other hand, DL-Met showed promising potential as a source of in ovo feeding in TETRA SL chicks, improving intestinal development compared to L-Met. Dietary supplementation of DL-Met and L-Met have similar effects on early TSL chicks' development and feather growth but may have different impacts on hematological parameters.