The effect of dietary crude protein concentration on growth performance, carcass composition and nitrogen excretion in entire grower-finisher pigs

Abstract

Two experiments, a performance experiment (n = 72) and a nitrogen balance (n = 16) experiment were conducted to evaluate the effects of dietary crude protein (CP) concentration on growth performance, carcass characteristics and nitrogen excretion of pigs. Dietary CP concentrations in experimental diets (g/kg) were 207.5, 170, 150 and 122.5 for treatments 1, 2, 3 and 4, respectively, and were offered to individually-fed entire-male grower-finisher pigs (45 to 95 kg). The diets were formulated to contain 13.7 MJ digestible energy and 11 g total lysine/per kg. Synthetic lysine, methionine, threonine and tryptophan were added to achieve ideal protein status. There was a linear increase in food intake as CP concentration decreased (P < 0.05). There was a quadratic response in daily live-weight gain and food conversion ratio (P < 0.05) to the change in CP concentration (P < 0.05), with an improvement in daily gain and food conversion ratio occurring as CP concentration declined to 150 g/kg and a deterioration in these parameters thereafter. There was a linear decrease (P < 0.05) in lean meat proportion as CP concentration decreased. There was a linear decrease in urinary output (P < 0.05), urinary pH (P < 0.01) and slurry pH (P < 0.05) as dietary CP concentration decreased. There was a quadratic response in urinary nitrogen output (P < 0.05), total nitrogen output (P < 0.05) and N utilization as dietary CP decreased. In conclusion, a dietary CP level of 150 g/kg was optimal in terms of growth performance and reduced nitrogen excretion.