Methionine is the first-limiting amino acid for broilers and plays a critical role in immune function. This study investigated the impact of graded supplemental levels of methionine in broilers undergoing a lipopolysaccharide (LPS) challenge. A total of 336 male broilers (Ross 308) were housed in batteries and allotted to 1 of 6 dietary treatments, with 7 replicates of 8 birds per replicate. Diets were provided in a 2-phase feeding program with a common starter diet and experimental grower diets provided d 0-10 and 10-28, respectively. Grower diets included a basal diet (0.136% digestible Met) supplemented with 0.360% L-Cys (0%DLM) and five other supplemented diets with graded levels of DL-Met (0.072%DLM- 0.360%DLM, with 0.072%DLM increments). To ensure the only limiting amino acid would be Met, other amino acids were included at approximately 15% over the AMINOChick 3.0 recommendations. All diets were provided ad libitum throughout the study. On study d 25 [0 hours post- stimulation (HPS)], all birds were challenged intraperitoneally with LPS derived from E. coli (O127:B8) at 2.0 mg/kg BW with 1 bird per pen was euthanized for sample collection at 5 HPS. Body weight gain during the grower phase was lowest (170 g, P < 0.01) in 0%DLM compared with 0.216%DLM or higher (1,067 g, 1,103 g and 1,112 g, respectively). Birds receiving 0%DLM had the least efficient feed conversion ratio (3.56 g/g, P < 0.01) compared with treatments ≥ 0.216%DLM (1.5). The treatments ≥ 0.216%DLM had, on average, 1.07 percentage points lower (P < 0.01) relative liver weights (%BW) at 5 HPS compared with 0%DLM (4.35%). Plasma concentrations of the acute phase protein, α-1-acid glycoprotein (AGP), were elevated (180. 3 μg/mL, P < 0.01) in 0%DLM compared with 0.144%DLM (88.3 μg/mL) and 0.288%DLM (76.5 μg/mL) treatments; however, there were no differences in interleukin-6 plasma concentrations.
In conclusion, broilers receiving diets deficient in Met exhibited a heightened response to LPS stimulation, as evident by the highest AGP production from hepatocytes, which may have contributed to increased relative liver weights. However, DL-Met supplementation ameliorated the effect of LPS as evidenced by benefits to growth performance, relative liver weights, and AGP concentrations.