Amino acid supplementation and substitution of soybean meal in crude protein- and phosphorus-reduced diets for grower-finisher pigs: Effects on performance and modelled environmental impact

Pigs’ N and P excretions are partially lost as NH3 or phosphate, resulting in potential environmental pollution and health risk for humans and animals. A study was conducted to investigate if supplementation of microbial phytase and free amino acids (AA) allows to decrease monocalcium phosphate (MCP) and solvent extracted soybean meal (SBM) in N- and P-reduced diets, and if these feeding strategies decrease environmental impacts while maintaining growth performance and meat quality traits. The impacts on greenhouse gas emissions (global warming, GW) and on acidifying emissions were modelled. Therefore, a total of 192 mixed-sexed pigs (body weight, BW: 32.6 ± 0.3 kg) were randomly allocated to 4 dietary treatments (4 pens per treatment and 12 pigs per pen, 48 pigs per treatment). Three-phase feed, supplemented with individual AA to maintain appropriate digestible AA to Lys ratios, were fed. The control treatment (CON) was formulated to contain 185 to 150 g kg-1 CP (as-fed). In the ‘low reduction’ treatment (LRT) and the ‘high reduction’ treatment (HRT), SBM and thus CP contents were reduced (LRT: 185 to 123 g kg-1; HRT: 161 to 123 g kg-1; as-fed). In the ‘alternative protein’ treatment (APT), SBM was completely replaced with rapeseed meal and faba beans to achieve CP contents of 169 to 123 g kg-1, close to HRT. Monocalcium phosphate was not supplemented in all treatments after the starter period (60 kg BW). Average daily gain (ADG) and gain to feed-ratio (G:F) did not differ between CON and other treatments during the overall grower-finisher period. Pigs of HRT and APT showed less lean compared to pigs of CON, being correspondent with the reduced loin muscle of those animals (P < 0.05). The meat quality traits did not differ between treatments although SBM per pig was markedly reduced or totally replaced (16, 13, 6.5, and 0 kg SBM per pig in CON, LRT, HRT, and APT, respectively). Nitrogen excretion was reduced (P < 0.05) by 13, 20, and 12% in LRT, HRT, and APT, respectively, compared to pigs fed the CON diet. Phosphorus excretion was reduced by 23, 25, and 5% in LRT, HRT, and APT, respectively, compared to CON. Consequently, the lower N intake reduced acidification and GW impacts by up to 14% and 7%, respectively. Results indicate that CP- and P-reduced diets for grower-finisher pigs are effective in lowering N and P releases into the environment, while growth performance and meat quality traits are maintained.