Characterization of the feed intake and acute -phase protein responses of pigs following an acute immune challenge with lipopolysaccharide

This series of studies were designed to evaluate the acute-phase response in pigs following an immunological challenge with lipopolysaccharide (LPS). The first experiment utilized six pigs (initial BW = 62.6 +/- 1.3 kg) that underwent repeated injection of LPS at 15 mug/kg BW every other day for a period of nine days. Pigs became tolerant to the LPS challenge following the third injection as indicated by the attenuation of the suppressions in feed intake. Following the initial LPS challenge, one of pig died between 12 and 24 h and the other pig failed to consume any feed for a period of 3 d. To investigate this hypersensitivity, 192 pigs (initial BW = 39.9 +/- 3.6 kg) were injected with 15 mug/kg BW LPS and changes in feed intake were measure over a 48 h period. This response is defined as the acute feed intake response (AFIR) and is calculated as the ADFI from 0 to 48 h divided by the ADFI from minus 48 to 0 h relative to the LPS challenge. This value is then multiplied by 100%. The mean AFIR for these pigs was 54.7 +/- 17.4%. This data was normally distributed and those pigs have an AFIR less than or greater than two times the standard deviation from the mean were considered hyper-responsive and hypo-responsive, respectively. Based on these observations, the used of the AFIR of pigs following an initial immune challenge with LPS can be used to identify hyper- and hypo-responsive pigs. The second experiment evaluated the AFIR, serum profiles of cortisol and tumor necrosis factor-alpha (TNF-alpha), and the subsequent growth performance of two genotypes (Line A and B) of pigs following an LPS challenge. No consistent genotype differences were observed in AFIR or serum profiles of cortisol and TNF-alpha. Pigs were categorized based on AFIR to evaluate subsequent growth performance, however, no differences were associated with AFIR categorization. Line A pigs tended to have greater average daily gain (P < 0.10) and greater gain-to-feed ratios (P < 0.01) than Line B pigs. The data from the second experiment indicated no differences were ascertainable in the immune response of these two genotypes of pigs. The final experiment was designed to evaluate the AFIR and acute-phase protein (APP) responses of two genotypes and genders of pigs (initial BW = 21.3 +/- 0.48 kg) to three levels of LPS (0, 25, or 50 mug/kg BW). Measures of AFIR decreased quadratically with increasing LPS dose (P < 0.05). No genotype differences were observed in AFIR. Three barrows and no gilts died following the LPS challenge (P < 0.10). Barrows also had higher d 0 haptoglobin (HPT; P < 0.03) and greater increases in ceruloplasmin (Cp; P < 0.05) concentrations than gilts. No effect of LPS treatment was observed in serum C-reactive protein, Cp, or HPT concentrations (P > 0.10). Serum amyloid A (SAA) concentrations increased quadratically with increasing LPS dose (P < 0.02). The results of this study indicate barrows may be more sensitive than gilts to an LPS challenge and SAA appears to be a viable biomarker of immune system activation in pigs. Overall, these experiments indicate measuring acute changes in feed intake may serve as an accurate means of evaluating the acute phase response in pigs. In addition, no differences in immune system activation were observed between the genotypes evaluated in these experiments.