Residual feed intake (RFI) is defined as actual feed intake minus the expected feed intake of individual animal and it was first proposed as an alternate measure of feed efficiency by (Koch et al 1963). RFI is a heritable character and heritability of RFI as 0.14. selection for traits associated with feed conversion efficiency should lead to greater profitability of dairying. Residual feed intake is a useful selection criterion for greater feed efficiency. The experiment was conducted at Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana . The two roughage: concentrate diets, namely 50:50 (50% roughage: 50% concentrate), 60:40 (60% roughage: 40% concentrate) were made. Twenty four lactating crossbred cows with average milk yield and week of lactation were taken. Twelve cows were divided in to two groups of six animals each and fed ration with 60:40 roughage: concentrate ratio (R_LC). The intake of OM and CP were significantly (p <0.05) high in R_HC hereas intake of ADF and NDF were significantly (p <0.05) high in R_LC. The roughage to concentrate ration has non­significant effect on the intakes of CHO, EE, NE, and ME. The RFI calculated based on DMI were statistical in both the groups. The digestibility of CP and EE were significantly (p <0.05) high in RHC compared to R_LC ration but that of ADF was significantly (p < 0.05) high in RLC compared to R_HC ration. The RFI of R_HC had significantly negative (p<0.05) effect on milk protein % but had no effect on milk production, milk energy yield, metabolic body wt., change/kg m.wt, and fat %, fat yield, protein yield and FCM . Nutrient digestibility of R_HC is significantly (p <0.05) higher for CP, EE as compared to R_LC and that of ADF had significantly (p <0.05) higher in RLC. The milk yield and protein yield of R_HC was significantly (p <0.05) higher than R_LC. Nutrient digestibility of R_HC is significantly (p <0.05) higher for CP, EE as compared to R_LC and that of ADF had significantly (p 0.05) higher in RLC. The correlation of RFI with m.b.wt, fat yield, protein yield, FCM was positively significant (p <0.05). RFI with milk yield was significantly (p <0.05) and negatively correlated.

Keywords: RFI; Roughage to Concentrate Ratio; Lactating Crossbred Cows.