Determining the effects of manganese source and level on growth performance and carcass characteristics of growing-finishing pigs

Two experiments were conducted to determine the effects of Mn source and level on finishing pig growth performance and carcass characteristics. Dietary treatments were arranged in a 2 x 3 factorial with main effects of Mn source (MnSO4; Eurochem, Veracruz, Mexico, or Mn hydroxychloride (IBM); Micronutrients, Indianapolis, IN) and increasing added Mn (8, 16, and 32 mg/kg of complete diet). The trace mineral premix was formulated without added Mn. Copper was added to all diets at 10 and 150 mg/kg in Exp. 1 and 2, respectively. In both experiments, 1,994 pigs (PIC; 337 x 1050; initially 34.5 +/- 0.50 and 40.0 +/- 0.77 kg) were used with 27 pigs per pen and 12 replicates per treatment. Diets were corn-soybean meal-distillers dried grains with solubles-based and were fed in four phases. In Exp. 1, there was a marginal Mn source x level interaction (quadratic, P = 0.057) for overall feed efficiency (G:F), with a decrease then increase in pigs fed IBM, but G:F increased with increasing Mn from MnSO4. There was no evidence for Mn source differences for average daily gain (ADG), average daily feed intake (ADFI), or body weight (BW), but pigs fed 16 mg/kg Mn, regardless of source, tended to have decreased (quadratic, P < 0.05) ADG and final BW compared with other levels. For carcass yield, there was a tendency for Mn source x level interaction (quadratic, P = 0.075), where carcass yield did not change by increasing MnSO4 but was greatest for 16 mg/kg Mn from IBM. Loin depth increased (source x level, P = 0.041) for pigs fed increasing Mn from MnSO4 but decreased when Mn was increased from IBM. Pigs fed the intermediate level of Mn tended to have the lightest HCW (quadratic, P = 0.071) and decreased loin depth (quadratic, P = 0.044). Liver Mn concentration increased (linear, P = 0.015) as added Mn increased and tended to be greater (P = 0.075) when supplied by MnSO4 compared with IBM. In Exp. 2, there was no (P > 0.10) Mn source x level interaction observed for ADG, ADFI, and G:F. Pigs fed IBM had increased (P < 0.05) final BW, ADG, and ADFI compared with pigs fed MnSO4. Pigs fed 16 mg/kg of Mn tended (P = 0.088) to have reduced ADFI when compared with pigs fed 8 and 32 mg/kg of Mn. In conclusion, there appears to be little benefit in growth performance by feeding more than 8 mg/kg of added Mn. When high levels of Cu were fed in Exp. 2, pigs fed IBM had improved growth performance when compared with those fed MnSO4. Further research is needed to understand the potential benefits of Mn hydroxychloride fed in conjunction with high levels of Cu on pig growth performance.