An in vivo procedure to determine nutrient requirements for growing pigs would have substantial cost advantages over serial slaughter and furthermore repeated measurements would allow estimation of protein requirements at each stage of growth. Serum urea concentration (Urea) has been proposed as a candidate indicator of protein requirement as over-supply of protein will increase Urea (Chen et al., 1995). The study estimated genetic variation in Urea at different stages of performance test and the relationships between Urea and performance traits.