Effect of Two Net Energy Feeding Programs in Combination with Ractopamine on Grow-finish Pig Growth Performance and Carcass Characteristics

Abstract Text: A total of 200 crossbred barrows (TOPIGS Tempo x TOPIGS 20) were blocked by BW (28.4±0.02 kg), housed 5 barrows/pen, and were randomly allocated to 1 of 4 treatments (10 pens/treatment) in a 2 x 2 factorial arrangement, with 2 net energy (NE) levels (Control vs. Low) and with or without 7.5 ppm ractopamine hydrochloride (RAC) during the last 21 d of a 105-d feeding trial. The objective was to evaluate pig performance to a decreasing net energy (NE) diet over the grow-finish period to validate TOPIGS feeding models. Diets were fed in 5-21 day phases.  Control diets were corn-soybean meal–corn DDGS based and Low NE diets were created by adjusting inclusion rates of soybean hulls and wheat midds, ingredient NE values were from NRC. Control NE levels (Mcal/kg) were 2.46, 2.45, 2.47, 2.50, 2.54, 2.64 and Low NE levels were 2.46, 2.39, 2.37, 2.34, 2.32, 2.39 (phase 1-5 and 5+RAC, respectively).  Diets were formulated on an equal SID Lys:NE basis within phase and phase 5 RAC diets had increased amino acids compared to non-RAC diets.  From d 0-84, Control fed pigs had great ADG (1.024 vs 0.983 kg/d; P<0.001), G:F (0.362 vs 0.354; P<0.009), and BW (114.4 vs 111.0 kg; P<0.001) than pigs fed Low NE diets but ADFI was similar (P<0.14).  During d 84-105, RAC increased (P<0.0001) ADG and G:F whereas ADFI increased (P<0.008) and G:F decreased (P<0.03) in pigs fed Low NE diets.  Overall, d 0-105, RAC increased (P<0.001) ADG, G:F, and final BW whereas feeding Low NE decreased (P<0.015) ADG, G:F, and final BW.   Feeding RAC increased (P<0.0001) carcass weight and carcass yield and Low NE diets decreased (P<0.0003) carcass weights (100.6, 104.8, 95.3,101.0 kg; Control, Control+RAC, LowNE, LowNE+RAC, respectively) and yields (75.2, 76.1, 73.8, 74.6%; Control, Control+RAC, LowNE, LowNE+RAC, respectively).  Both RAC and Low NE diets increased (P<0.006) carcass belly iodine values.  Overall NE utilization efficiency for live BW gain was greater for Low NE (P<0.04) and RAC (P<0.0001) diets (0.1374, 0.1444, 0.1402, 0.1471 kg/Mcal; Control, Control+RAC, LowNE, LowNE+RAC, respectively).  However, NE efficiency to carcass weight was only improved (P<0.0001) by RAC (0.1029, 0.1102, 0.1023, 0.1092 kg/Mcal; Control, Control+RAC, LowNE, LowNE+RAC, respectively).  Low NE diets reduced growth and carcass performance, but, feeding RAC improved performance regardless of dietary NE, and NE conversion to carcass weight was similar between NE diets and was improved by feeding RAC.

Keywords: net energy, ractopamine, grow-finish pig