One of the main issues currently facing the pig sector is how to use fewer feed resources and reduce nitrogen (N) and phosphorus (P) excretion without increasing feed costs. In this context, the aim of this study was to investigate impacts of restricting the intake of protein, essential amino acids and P on the growth performance and body composition of pigs. Forty-eight Swiss Large White pigs were allocated to four treatment diets, each comprising six females and six castrated pigs. The control (C) was fed a grower and a finisher diet to meet requirements for a weight of 40 and 80 kg, respectively. The other diets were deficient in N-: free of soya bean meal, -20% crude protein, digestible lysine, digestible methionine and digestible threonine; in P-: free of mineral phosphate, -15% (including phytase) and -47% (no phytase) digestible P in grower and finisher diets, respectively and in NP-: a combination of N- and P-. The statistical model included the sex, N and P effects and their interactions. All effects of N and P restriction were independent from each other (P > 0.05). The feed-conversion ratio was made worse by N restriction (2.47 vs. 2.73; P < 0.001), but not by P restriction (P > 0.05). Body lean content was decreased, while fat content was increased, by N restriction (P < 0.001), and bone mineral mass and density were decreased by P restriction (P < 0.001). N and P efficiency (ratio of excreted to ingested) was improved by 3.2 and 4.9 percentage points by the N restriction and P restriction, respectively (P < 0.001). These results illustrate effects of strong restriction of protein, digestible essential amino acids and digestible P and indicate that growing pigs without the use of mineral phosphate is realistic.
