Humic acid (MFG) and fat-protected butyric acid (BA) has been shown to modulate energy metabolism and inflammation. Therefore, the objectives of this study were to determine the effects of MFG and BA, alone and in combination, on growth performance and response to lipopolysaccharide (LPS)-induced inflammation in young pigs. An experiment was conducted using 448 crossbred weanling pigs, which were stratified by gender and BW and were randomly assigned to 1 of 4 dietary treatments in a 2 × 2 factorial arrangement consisting of control and MFG with or without BA. The pigs were housed at a density of 8 pigs/pen and with 14 pens/dietary treatment. Growth performance and feed intake were assessed for 35 d. To assess the inflammation-related properties of MFG and BA, on d 36 a subset of 48 pigs from each treatment was intramuscular injected with either sterile saline or Escherichia coli LPS (20 μg/kg BW; E. coli serotype O55:B5) for 4 h in a 2 × 2 × 2 factorial arrangement (± LPS, ± MFG and ± BA; n = 6 pigs/treatment group) to assess their febrile response as well as serum, liver, and muscle cytokine responses. Results from this study showed that neither BA nor MFG alone or in combination altered pig ADG, ADFI, and G:F. Moreover, in the presence of LPS, the combination of MFG and BA resulted in a 62% decrease (P = 0.08) in serum cortisol compared to when neither compound was added to the diet. In contrast, serum IGF-I was increased (P < 0.01) by 59% from the use of both MFG and BA, as opposed to when neither was added, with pigs subjected to LPS. However, both MFG and BA inclusion appear to have a complex role in modulating different aspects of the immune response to LPS, particularly when both are fed in combination. Humic acid also appeared to play a role in decreasing oxidative stress.

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