ESTIMATION BY REGRESSION-ANALYSIS OF ENDOGENOUS AMINO-ACID LEVELS IN DIGESTA COLLECTED FROM THE DISTAL ILEUM OF PIGS

An experiment was conducted to estimate by simple linear regression th e levels of endogenous amino acids in digesta collected from the dista l ileum in pigs. Six barrows, average initial BW 35 kg, were fitted wi th a simple T-cannula at the distal ileum and fed six diets according to a 6 x 6 Latin square design. Six cornstarch-based diets containing six levels of CP from soybean meal (4, 8, 12, 16, 20, and 24% CP, resp ectively) were formulated. Chromic oxide (.4%) was included as the dig estibility marker. Each experimental period consisted of 8 d. Ileal di gesta were collected, at 2-h intervals, for a total of 24 h during d 7 and 8. There were linear relationships (P < .001) between dietary con tents of apparent ileal digestible and total amino acids, irrespective of the ranges in graded dietary levels of amino acids. Determined wit h the regression technique, the endogenous levels of the indispensable amino acids (grams/kilogram of DMI) were as follows: arginine, .64; h istidine, .23; isoleucine, .46; leucine, .69; lysine, .47; methionine, .13; phenylalanine, .31; threonine, .69; and valine, .54. Differences in the ranges of graded dietary levels of amino acids resulted in lar ge differences in the estimated amounts of endogenous amino acids in i leal digesta. Furthermore, it seems that the levels of endogenous amin o acids, as grams/kilogram of DMI, were constant at different dietary levels of amino acids, whereas the contributions of endogenous amino a cids, as percentages of their dietary contents, decreased curvilinearl y with increasing dietary contents. Therefore, apparent ileal digestib ilities of amino acids were quadratically related to their dietary con tents until plateau digestibilities were reached, whereas the true ile al digestibilities of amino acids were independent of their respective dietary contents. Furthermore, true ileal amino acid digestibilities should be determined from their corresponding plateau apparent ileal d igestibilities. In conclusion, the levels of endogenous amino acids in ileal digesta can be determined reliably from the linear relationship s between dietary contents of apparent ileal digestible and total amin o acids. An important methodological consideration in the determinatio n of endogenous amino acids by regression analysis is to design an app ropriate range of graded dietary levels of amino acids.