Effects of reduced CP diets, formulated on either an ME or NE basis, on growth performance and carcass characteristics of growing-finishing swine

Abstract Text: Barrows and gilts (n = 245) were used to compare the effects of reduced CP (RCP) diets, formulated on an ME (3.43 Mcal/kg) or NE (2.58 Mcal/kg) basis, on performance and carcass characteristics. Pigs were blocked by initial BW, and, within blocks, pens of pigs (5 pigs/pen) were assigned randomly to 1 of 5 dietary treatments: corn-SBM diets formulated to meet SID ideal AA ratio requirements (C; 21.1, 20.2, 17.4, 15.2, and 18.2% CP for phases 1, 2, 3, 4, and 5, respectively); diets formulated on the same ME or same NE basis as C-diets to meet the SID ILE or VAL:LYS ratio (RCP1; 19.1, 17.1, 14.6, 12.8, and 16.2% CP for phases 1 through 5, respectively); or diets formulated on the same ME or same NE basis as C to meet the SID HIS:LYS ratio (RCP2; 17.0, 15.1, 12.9, 11.2, and 14.7% CP for phases 1 through 5, respectively). Paylean (10 mg/kg) was included in all diets during the last 3 wk of finishing. Individual pig BW and pen feed disappearance were recorded at the end of each phase to calculate ADG, ADFI, and G:F. At an average BW of 127 kg, all pigs were slaughtered at a commercial pork plant. Carcass data were collected before chilling, and randomly selected pork loins (3/pen) were captured for pork quality data collection. ADG increased, then decreased (quadratic, P ≤ 0.06) with decreasing CP in ME- and NE-diets; however, neither ADFI (P ≥ 0.11) nor G:F (P ≥ 0.14) were affected by dietary treatments. HCW increased, then declined to C (quadratic, P ≤ 0.06) with decreasing CP in both ME- and NE-diets, but dressing percentage increased with decreasing dietary CP (linear, P = 0.02) in ME-diets. LM depth decreased (quadratic, P = 0.07) with decreasing CP in NE-diets, but neither fat depth (P ≥ 0.16) nor estimated lean yield (P ≥ 0.21) differed among dietary treatments. LM drip loss percentage increased (quadratic, P = 0.03) with decreasing CP in NE-diets. Visual LM color scores decreased (quadratic, P ≤ 0.02) as CP decreased in ME-diets; yet, instrumental color measures did not (P ≥ 0.12) differ among dietary treatments. Results indicate that growth rate was reduced at the highest level of CP reduction in ME- or NE-based diets, without affecting G:F or carcass composition; however, the effects of RCP on pork quality traits were more evident when diets were formulated on a NE basis.

Keywords: Reduced crude protein, Net energy, Metabolizable energy, Swine