Effects of Amino Acid Supplementation of Reduced Crude Protein Diets in Growing/Finishing Pigs.

A study was conducted to determine the impact of increased crystalline amino acid content in reduced crude protein diets on growth performance and calculated lean tissue gain of growing/finishing pigs.  A total of 420 pigs were blocked by initial BW into 7 weight blocks and allotted to pens (6 pigs/pen by gender); pens were randomly assigned to 1 of 5 dietary treatments fed during phases 1 (22 to 37 kg), 2 (37 kg to 56 kg), 3 (56 to 77 kg), 4 (77 to 104 kg), and 5 [(104 to 129 kg); 10 ppm added ractopamine].  Diets were formulated 1) to 95% of the average standardized ileal digestible (SID) lysine requirement for barrows and gilts; 2) to exceed the SID amino acid ratio recommendations for other indispensable amino acids by 2% for all phases; and 3) to keep ME and g lysine/Mcal ME constant across treatments.  For each phase, control diets were devoid of synthetic amino acids.  Lysine was added in equal increments [phase 1 (0.188%), 2 (0.179%), 3 (0.146%), 4 (0.121%) and 5 (0.149%)] to each of the 4 remaining treatments within phase.  Individual BW and pen feed disappearance were recorded at the end of phases 1 to 4, and weekly during phase 5 to allow calculation of ADG, ADFI and G:F. Tenth rib, ¾ midline back fat depth and loin-eye area were measured by ultrasound at the end of each phase (3 pigs/pen) to allow estimation of lean tissue gain.  Results of this study indicate similar performance in treatments 1 through 4, but a detrimental impact of reducing crude protein in treatment 5.  Data from this study will be used to support enhancement of existing, or development of new robust and accurate, process-based animal growth, manure nutrient output, manure gas emissions and Life Cycle Assessment and Cost models.  These models will allow better optimization of nutrient requirements, animal growth, and GHG emission from swine production systems.