|Yen, Jong Tseng|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2003
Publication Date: 4/1/2004
Citation: YEN, J., KERR, B.J., EASTER, R.A., PARKHURST, A.M. DIFFERENCE IN RATES OF NET PORTAL ABSORPTION BETWEEN CRYSTALLINE AND PROTEIN-BOUND LYSINE AND THREONINE IN GROWING PIGS FED ONCE DAILY. JOURNAL OF ANIMAL SCIENCE. 2004. v. 82. p. 1079-1090. Interpretive Summary: Lowering dietary protein level and supplementing crystalline amino acids reduce nitrogen excretion and environmental pollution. However, crystalline amino acids are absorbed more rapidly than protein-bound amino acids in pigs. This can cause a temporary surplus of absorbed crystalline amino acids and result in an imbalance of amino acids at the sites of protein synthesis if a diet supplemented with crystalline amino acids is fed only once daily. Although most pigs are generally allowed ad libitum access of feed, inefficient utilization of supplemental crystalline amino acids resulting from once daily feeding is a concern in gestating sows and pigs that are restricted-fed in many research studies.
Technical Abstract: Portal absorption of amino acids (AA) during the 6-h postprandial period was measured in eight gilts (48.5 ± 1.6 kg BW). The pigs had chronic catheters placed in the portal vein, carotid artery, and ileal vein, and were trained to be fed once daily 1.2 kg of a standard grower diet. Blood samples were taken every 30 min for 4 h and then hourly until 6 h after feeding. The first set of blood samples was taken after pigs were fed a meal of the test 16% CP corn-soybean meal diet (16% CP) or the test 12% CP corn-soybean meal diet supplemented with crystalline lysine, threonine, and tryptophan (12% CP + AA) to equal the three AA levels in the 16% CP diet. Pigs were then fed the standard diet for 2 d. Following that, blood samples were again taken after the pigs were fed a meal of the test diet that was not given to them at the first sampling period. Net portal AA absorption was calculated by multiplying porto-arterial plasma AA concentration difference by portal vein plasma flow rate (PVPF), estimated by an indicator-dilution technique employing p-aminohippuric acid as the indicator infused into the ileal vein. Plasma concentrations of lysine and threonine of pigs were affected by the diet × time interaction (P < 0.01). Portal and arterial plasma lysine concentrations in pigs attained the maximum level at h 1 postprandial when the 12% CP + AA diet was fed, but reached the peak level at h 2.5 postprandial when the 16% CP diet was given. Portal and arterial plasma threonine concentrations rose to the maximum level at h 0.5 and 1.0 postprandial, respectively, when the 12% CP + AA diet was given, but both concentrations reached the peak level at h 2.5 postprandial when the 16% CP diet was fed. The PVPF of pigs over the 6 postprandial h was less (P < 0.01) when the 12% CP + AA diet than the 16% CP diet was fed. Net portal absorptions of lysine and threonine were also affected (P < 0.05) by time × diet interaction. The peak portal absorption of both lysine and threonine in pigs appeared at h 0.5 after feeding when the 12% CP + AA diet was given, but at h 2.5 postprandial with the feeding of the 16% CP diet. The early appearance of peak portal absorption of lysine and threonine from feeding the 12% CP + AA compared with the 16% CP diet indicates that crystalline lysine and threonine are absorbed more rapidly than protein-bound lysine and threonine in pigs fed once daily.