Preventive–curative functional amino acid–supplemented diet improves health, growth performance, and resilience of growing pigs under an immune challenge

Immune system stimulation (ISS) alters the metabolic demand for amino acids (AA), and amino acid-based nutritional strategies may mitigate performance reduction in pigs subjected to sanitary challenge conditions. This study aimed to evaluate the effect of extra supplementation of a combination of functional AA (FAA, +20% threonine, methionine, and tryptophan) preventively (pre-ISS), curatively (during-ISS) or both on the performance of growing pigs challenged with Salmonella Typhimurium (ST) and poor housing conditions. Fifty-two entire male pigs (21.7 ± 4.6 kg) were allocated to four dietary treatments, with a control AA profile diet fed throughout the experimental period (Control; NRC, 2012) or a FAA supplemented diet (FAA+; supplied +20% Trp: Lys, Thr: Lys, and Met+Cys: Lys above Control) fed only before the ISS (FAA Preventive), during the ISS (FAA Curative), or before and during the ISS-period (FAA Continuous). On day 0, after a 7-d pre-ISS-period (day -7 to -1, pre-ISS), all pigs were inoculated with ST (2 × 109 CFU/mL). Additionally, manure from a commercial pig farm was spread on the solid concrete floor, and the room was not cleaned during the ISS-period for 4 wk (0 to 28 d). Thereafter, all pigs received the same standard diet for 9 wk (days 29 to 91), and the facilities were cleaned daily. Pigs were group-housed and fed using five electronic precision feeders during pre-ISS and ISS-period (-7 to 28 d). There was no effect of providing additional FAA before the ISS-period on growth performance (P > 0.10), indicating that the control diet met at least the requirements under non-challenged conditions. Rectal temperature increased by 1.25 °C on day 1 of the ISS-period (P < 0.05) and remained higher than pre-ISS during days 2 to 7 of the ISS-period (P < 0.05). Control group had higher rectal temperature than the FAA Preventive (P < 0.05). Serum haptoglobin was higher on day 7 and 28 (P < 0.05), while albumin was lower on day 28 (P < 0.05), with lower concentrations in the control group compared with the FAA curative (P < 0.05). Higher final BW (P < 0.05), ADG (P < 0.05), and G:F (P < 0.05) were observed in the FAA Continuous compared to the Control. On day 28, FAA curative pigs showed higher total body protein content than FAA preventive pigs (P < 0.10). Nitrogen utilization efficiency improved by 32.6% (P < 0.05) for the FAA Curative compared with the Control. There were no remaining effects of treatments on BW or body composition on day 91 (P > 0.10). In conclusion, the combination of short-term preventive and curative strategies with FAA dietary supplementation modulated the immune response and improved the growth performance of growing pigs under chronic immune system stimulation.