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Effect of dietary lysine on plasma amino acid profile of finishing pigs
Muscle growth requires constant amino acid (AA) supply from the blood and, therefore, the profile of plasma AAs is a critical parameter to manage in order to maximize the lean gain of pigs. This research was conducted to study how dietary lysine affects plasma AA profile in finishing pigs. Eighteen crossbred (Yorkshire × Landrace) finishing pigs (9 barrows and 9 gilts; initial BW 92.3 ± 6.9 kg) were individually penned in an environment controlled barn. Pigs were assigned to 3 dietary treatments according to a Randomized Complete Block Design with sex as the block and pig as the experiment unit (6 pigs/treatment). Three corn and soybean-meal based diets were formulated to contain three levels of total lysine for the three treatments, which were 0.43, 0.71, and 0.98% lysine (as-fed basis) for Diets I (lysine deficient), II (lysine adequate), and III (lysine excess), respectively. After 4 weeks on the trial, jugular vein blood was collected and the plasma samples were obtained by centrifugation. The concentrations of 24 AAs were determined using appropriate HPLC methods. Five distinct patterns of plasma AA concentration alteration were observed: (1) The plasma lysine level followed the same trend as the dietary lysine level and there were significant differences (p < 0.05) among the three treatments. (2) The plasma asparagine concentration was increased (p < 0.05) with Diet III, but it was not with Diet I, when compared with Diet II. (3) There was no difference between Diets II and III in the plasma concentration of alanine, glutamic acid, glycine, or leucine, but the concentrations of these AAs were reduced with Diet I (p < 0.05). (4) The concentrations of arginine, histidine, citruline, threonine, valnine, isoleucine, or phenylalanine were increased with Diet I when compared to Diet II (p < 0.05), but there was no difference in the concentrations of these AAs between Diets III and II. (5) There were no differences (p > 0.05) among the three diets in the plasma concentrations of aspartic acid, β-alanine, cystine, glutamine, methionine, ornithine, proline, serine, taurine, tryptophan, or tyrosine. These five distinct patterns of plasma AA concentrations indicated complex metabolic interactions between dietary lysine and other AAs. Thorough understanding of these interactions will assist swine nutritionists to manage plasma AA profile via dietary AA supply. This research was supported by USDA-NIFA Hatch/Multistate Project 233803.
Keywords: lysine, amino acid profile, plasma, dietary supply, swine