Comparative alkaline hydrolysis for the determination of tryptophan in feedstuffs and determination of the tryptophan requirements for 5 to 20 and 20 to 50 kilogram pigs

Abstract

Thirty two feedstuffs and lysozyme were hydrolyzed using either Ba(OH)2, NaOH or LiOH and analyzed by ion-exchange chromotography to determine which gave the most accurate and repeatable results. The tryptophan recovery from most feedstuffs was essentially the same for all methods although recovery of Trp from lysozyme was greatest for LiOH. Repeatability was lower for LiOH (70%) than for Ba(OH)2 or NaOH (90%). The NaOH method requires appears to optimize accuracy and repeatability. Five group feeding trials with 705 weaned pigs and three individual feeding trials with 230 grower pigs were conducted to reevaluate the Trp requirement for pigs fed low-protein corn-SBM diets. The average Trp content of the corn (.048%) and SBM (.57%) used in all trials was determined by the Ba(OH)2 method. Each series began with a titration study in which the basal diet contained 67% of the Trp and at least 105% of the NRC requirements for the other amino acids (AA). Trp levels ranged from .10 to .16% and .08 to .12% in the first starter and grower trials, respectively, and from .12 to .22% in starter trials 2 and 3. Starter trial 4 and grower trial 2 were designed to determine if the Trp requirement found in the previous trials was adequate when additional threonine was added above the suggested NRC requirement. The last starter and grower trials evaluated the feasibility of using corn-SBM diets formulated to the Trp requirement and supplemented only with synthetic lysine. Growth of 5 to 20 kg pigs was maximized at .14% dietary Trp. As the amount of AA supplied by SBM protein increased, ADG also increased in comparison to the control diets. Similarly, as the present synthetic AA in the diet decreased, so did the Trp requirement. A similar effect was observed with the grower pig. The starter pig required .14% dietary L-Trp in a 14.7% protein corn-SBM diet and the grower pig required a minimum of .10% dietary L-Trp in a 11.7% protein corn-SBM diet. Starter and grower pigs fed low-protein, Lys-fortified corn-SBM diets can perform optimally when fed diets formulated to the Trp requirements suggested in these trials. However, the addition of additional AA except Lys (e.g., Thr) tends to increase the apparent Trp requirement.