A comparison between feeding a single diet or phase feeding a series of diets, with either the same or reduced crude protein content, to growing finishing pigs

A study was designed to determine if pig performance and lysine conversion ratio would be improved by phase feeding a series of diets with either the same, or with reduced overall mean crude protein (lysine) content, compared with providing a single diet throughout the growing-finishing period. Four hundred and forty-eight group-penned pigs (no. = 32 groups) were assigned at random to one of four treatments : single diet (SD : 11.1 g lysine per kg), high lysine (HL : 12.2, 11.6, 11.1, 10.5 and 10.0 g lysine per kg), medium lysine (ML : 11.1, 10.5, 10.0, 9.5 and 8.9 g lysine per kg) and low lysine series of diets (LL : 10.0, 9.5, 8.9, 8.4 and 7.8 g lysine per kg). The mean lysine contents of the treatments were 11.1, 11.1, 10.0 and 8.9 g/kg for SD, HL, ML and LL respectively. There were five 2-week phases from 38.3 kg to slaughter at 97.3 kg live weight. LL pigs had lower carcass average daily gain (709 v. 742 g/day; P<0.05) and poorer carcass FCR (P<0.05 : 2.95 v. 2.84 kg/kg) than SD pigs. Daily lysine intake was lower for pigs on HL (P<0.05 : 22.5 g/day), ML (P<0.001 : 20.9 g/day) and LL (P<0.001 : 18.2 g/day) compared with SD (23.4 g/day). Live weight lysine conversion ratio was better for HL (P<0.05 : 26.9 g/kg), ML (P<0.001 : 24.5 g/kg) and LL (P<0.001 : 22.6 g/kg) pigs compared with SD pigs (27.6 g/kg), but carcass lysine conversion ratio was only better for pigs on the ML (P<0.001 : 27.9 g/kg) and LL (P<0.001 : 25.7 g/kg) treatments compared with SD (31.6 g/kg). Nitrogen intake was lower for LL pigs than SD pigs (P<0.001 : 3.45 v. 4.03 kg). Estimated nitrogen excretion was lower for ML (P<0.01 : 2.16 kg) and LL (P<0.001 : 1.85 kg) pigs than SD pigs (2.47 kg). Nitrogen deposition rate was lower for pigs on the LL compared with the SD treatment (P<0.05 : 22.3 v. 23.2 g/day). Although phase feeding diets with the same mean lysine content (11.1 g/kg) as a single diet over the growing-finishing period resulted in similar pig performance, reduced overall daily lysine intake and improved lysine conversion ratio, there was no effect on carcass characteristics or carcass lysine conversion ratio. Reducing the overall mean lysine content to either 10.0 or 8.9 g/kg improved lysine conversion ratio and reduced nitrogen excretion. However, reducing the overall mean lysine content of the diet to 8.9 g/kg had a negative effect on pig growth performance.