Background: In commercial poultry production, where feed expenses account for about 70% of total costs, improving feed efficiency is crucial for profitability and sustainability. CSML exhibits a multi-Colored plumage and brown eggshells, closely resembling native desi birds, making it highly desirable for crossbreeding to improve indigenous poultry. 
 
Methods: A total of 100 CSML chicks were reared individually from 2 to 12 weeks of age to assess Feed Conversion Ratio (FCR), Residual Feed Intake (RFI), Residual body weight Gain (RG) and Residual Intake and Body Weight Gain (RIG). Based on these traits, birds were divided into high feed efficient (HFE) and low feed efficient (LFE) groups, with HFE representing the top 20% and LFE the bottom 20%. 
 
Result: HFE birds showed significantly better performance, gaining 7.87% body weight gain, consuming 9.96% less feed, achieved 17.25% better FCR and demonstrating improved RFI (179.86%), RG (220.03%) and RIG (182.50%) compared to LFE birds. Gene expression analysis via real-time qPCR revealed upregulation of SGLT1 (nutrient transporter) and GHRL (growth-related) genes and down regulation of CDx (gut development) genes in HFE birds, suggesting their role in feed efficiency. The study concludes that HFE CSML birds exhibit enhanced feed efficiency traits than LFE group, which can be used for production of high feed efficient hybrids. 
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Expression Profile of Feed Efficiency Related Genes in High and Low Feed-efficient Colored Synthetic Male Line (CSML) Broiler Chickens