262 Weaning-Induced Changes in Tissue Cysteine Utilization in Pigs

Abstract

Abstract Weaning stress in pigs is associated with low and variable feed intake, poor nutrient utilization, and high feed costs. Cysteine is a sulfur amino acid with key roles in pig production, but how cysteine metabolism and requirements are affected by weaning stress should be better defined. The objective of this study was to determine weaning-induced changes in tissue cysteine metabolism. Pigs (initial BW = 7.23 ± 0.68 kg) were either weaned at 21 d age and euthanized at 23 d age (W; n = 9) or remained with the sow and euthanized at 23 d age (NW; n = 9). Weaned pigs were fasted to simulate acute nutritional stress but had free access to water. At euthanasia, blood, liver, jejunum, and ileum tissues were collected. Plasma and tissue amino acids and amino thiols were analyzed by HPLC. The abundance of proteins central to liver cysteine utilization were determined by immunoblot and enzyme activity assays. Glutathione (GSH) concentrations were less in jejunum (1,379 versus 1,720 ± 70 nmol/g; P < 0.01) and ileum (1,497 versus 1,740 ± 74 nmol/g; P < 0.05) in W than NW pigs. However, liver GSH concentration was not different between W and NW pigs (P > 0.10). While cysteine in jejunum and ileum were not affected by weaning (P > 0.10), γ-glutamylcysteine (γ-GC), the immediate precursor of GSH, declined in both jejunum (9.7 versus 14.3 ± 1.4 nmol/g; P < 0.01) and ileum (6.4 versus 11.2 ± 0.8 nmol/g; P < 0.001) in W compared with NW pigs. In liver, cysteine concentration was greater in W compared with NW pigs (417 versus 298 ± 33 nmol/g; P < 0.05). Although liver cysteine was greater in W pigs, liver activity of glutamate cysteine ligase (GCL; 2.49 versus 4.15 ± 0.25 nmol γ-GC/(mg protein•min); P < 0.001) and glutathione synthetase (GSS; 1.54 versus 1.92 nmol GSH/(mg protein•min); P < 0.001), enzymes needed for GSH production, were less in W than NW pigs. Immunoblot analysis of the catalytic subunit of GCL (GCLC; P < 0.05) and modifier subunit of GCL (GCLM; P = 0.057) were also lower in W compared with NW pigs, but GSS was not different between groups (P > 0.10). While plasma taurine was lower in W compared with NW pigs (64 versus 128 ± 7 µmol/L, P < 0.001), liver taurine was greater in W compared with NW pigs (4,726 versus 2,250 ± 471 nmol/g; P < 0.01). Despite an increase systemic and liver availability of cysteine, the rate-limiting amino acid for GSH synthesis, small intestine GSH concentrations decline. This suggests that systemic cysteine is not effectively utilized for gut GSH production in pigs after weaning.