Response to reduced dietary protein level on growth performance in growing Windsnyer pigs

The objective of the study was to determine the growth performance response to reduced dietary protein level and to identify the optimum level of protein for the performance in growing Windsnyer pigs. Maize-soybean-based diets were formulated to contain a protein level of 193 g/kg, 173.7 g/kg, 154.4 g/kg, 135.1 g/kg, 115.8 g/kg and 96.5 g/kg. The 193 g/kg (control diet) is the standard recommended by the National Research Council. The amino acid levels and net energy value were similar in all treatments. The study was conducted with five growing Windsnyer pigs per each protein inclusion level. The trial was carried out with individually caged pigs aged 4 months, weighing about 23 (SD = 1.39) kg. The experiment lasted a period of 8 weeks excluding 2 weeks of the adaptation period. The feed and water were offered ad libitum. The average daily feed intake (ADFI), average daily gain (ADG), feed conversion ratio (FCR), final body weight (FBW) and metabolic body weight (BW^0.75) were measured. Polynomial regression and piecewise regressions were used to analyse data. Decremental levels of protein did not affect (p > 0.05) ADFI and ADG. Reduced levels of protein influenced FBW, BW^0.75 and FCR (p < 0.05). A decreasing quadratic response was observed in FCR, as CP decreased from 193 g/kg to 135.1, FCR improved from 3.18 to 2.13 then suddenly decreased with the CP level. There was a quadratic increase in BW^0.75 and FBW as inclusion levels of protein were reduced (p < 0.05). They increased from 193 g/kg (FBW 39.5 and BW^0.75 12.8) protein level until 135.1 g/kg (FBW 45.1 and BW^0.75 14.6) then begun to decrease as dietary protein level was decreased further. Using stepwise piece (broken stick) methods, the optimum protein level for FCR was estimated to be at 135.1 g/kg (p < 0.05). The maximum level of dietary protein for BW and BW^0.75 was obtained at 135.1 g/kg. Reduction of the CP level in the Windsnyer pig diet beyond 138.3, 132.1 and 132.3 g/kg hinders the FCR, FBW and BW^0.75, respectively. Protein levels can be reduced from the standard recommendation level of 193 g/kg to 135.1 g/kg without compromising the growth performance of growing Windsnyer pigs.