Selection for feed efficiency elicits different postprandial plasma metabolite profiles in response to poor hygiene of housing conditions in growing pigs

Selection for residual feed intake (RFI), a measure of feed efficiency, may affect the ability of pigs to adapt their metabolism in response to poor environmental conditions. This study was conducted to compare postprandial plasma concentrations of insulin, energy related metabolites, and amino acids measured after a 6-week challenge consisting of exposure to good or poor hygiene of housing conditions of 24 growing pigs divergently selected for low-RFI (LRFI) and high-RFI (HRFI). Blood indicators of immune responses were assessed from samples collected before (week 0 or W0), and 3 (W3) and 6 weeks (W6) after pigs transfer to their respective housing hygiene conditions. Plasma haptoglobin concentrations and blood neutrophil granulocyte numbers were greater in poor than in good conditions at W3. Plasma concentrations of total immunoglobulin G were greater ( p = 0.04) in poor than in good hygiene conditions at W6. At W6, pigs were fitted with an intravenous catheter for serial blood samplings. Low-RFI pigs had greater insulin ( p < 0.001) and lower triglyceride ( p = 0.04) average plasma concentrations than HRFI pigs in both conditions. In poor hygiene conditions, the peaks of insulin and glucose occured earlier and that of insulin was greater in LRFI than in HRFI pigs. Irrespective of genetic line, average plasma concentrations of histidine, isoleucine, leucine, methionine, threonine, valine, and alanine were greater in poor compared with good conditions. Only HRFI pigs had greater lysine, asparagine, proline, and tyrosine plasma concentrations in poor than in good hygiene conditions. Conversely, arginine, tryptophan, proline, and tyrosine plasma concentrations were lower only for LRFI pigs housed in poor hygiene conditions. The impact of poor hygiene of housing conditions on insulin, triglycerides, and AA profiles differed between RFI lines. More specifically, our results suggest that, contrary to HRFI, LRFI pigs increased or maintained their utilization of Trp, Arg, and Lys when housed in poor hygiene conditions. This difference may contribute to the better capacity of LRFI to cope with the poor hygiene of housing conditions.