Estimating standardized ileal digestible methionine requirements for gilts during gestation using whole-body nitrogen retention and describing plasma creatine, glutathione, and taurine concentrations.

A total of 70 gestating gilts (166 ± 13 kg initial BW on day 31 of gestation) were used to determine the standardized ileal digestible (SID) Met needed to maximize whole-body N retention and to describe the impact of dietary Met on indicators of Met utilization for roles beyond protein synthesis. Seven days prior to N balance measurements between days 38 and 41, days 53 and 56, days 87 and 90, and days 109 and 112 of gestation (periods 1, 2, 3, and 4, respectively), gilts were assigned to 1 of 7 dietary treatments (n = 10) that titrated SID Met between 50% and 150% of perceived requirements of 3.5 and 5.2 g SID Met/d (before and after day 90 of gestation, respectively) using dl-Met and in the presence of excess Cys in an incomplete randomized block design. Fasted blood samples were collected on days 38, 53, 87, and 109 to assess concentrations of plasma Met-derived metabolites. Contrast statements were used to determine linear and quadratic effects of the dietary inclusion level of SID Met and quadratic polynomial (QPM), broken-line linear, and broken-line quadratic (BLQ) ascending models were evaluated for the primary response variables. Whole-body N retention did not exhibit linear or quadratic relationships with increasing SID Met content in periods 1, 2 and 3, but inflection points were observed at 0.17% (3.8 g SID Met/d; QPM), 0.19% (4.2 g SID Met/d; BLQ), and 0.16% SID Met (3.5 g SID Met/d; QPM), respectively. Whole-body N retention increased (linear and quadratic; P < 0.001) with increasing SID Met content in period 4, optimized at 0.23% (6.0 g SID Met/d; QPM). Plasma creatine concentration did not exhibit linear or quadric relationships with increasing SID Met contents, but the QPM indicated inflection points at 0.17%, 0.17%, 0.22%, and 0.18% SID Met (3.8, 3.8, 4.9, and 4.7 g SID Met/d) on gestation days 38, 53, 87, and 109, respectively. Plasma concentrations of GSH tended to increase then decrease (quadratic; P = 0.096) on day 53 and tended to increase (linear; P = 0.095) on day 87 as SID Met increased; inflection points were observed at 0.16%, 0.17%, 0.21%, and 0.16% SID Met (3.5, 3.8, 4.6, and 4.2 g/d; QPM) on gestation days 38, 53, 87, and 109, respectively. Thus, the SID Met feeding recommendations provided by the NRC (NRC 2012. Nutrient requirements of swine. 11th rev ed. Washington D.C.: National Academy Press) gestating sow model are insufficient to maximize whole-body N retention of gilts throughout gestation in current production conditions, while the supply of SID Met might also influence Met utilization for metabolic fates beyond protein retention.