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Tryptophan Availability of Some Feedstuffs Determined by Pig Growth Assay¹

University of Illinois^,4,5,, Urbana 61801

Abstract

Three experiments were conducted with young pigs to measure the availability of tryptophan in soybean meal, meat and bone meal, cottonseed meal, corn and sorghum. In Exp. 1, a 17.5% crude protein corn and gelatin-based diet, deficient in tryptophan, was supplemented with graded levels of L-tryptophan to establish the growth response of 10- to 20-kg pigs to graded additions of dietary tryptophan. From these data the requirement for maximal growth was calculated to be .16% of the diet using a broken-line model. In Exp. 2, the effects of excess amino acids in a test feedstuff, i.e., soybean meal, on the growth assay method for estimating tryptophan availability was evaluated. The addition of excess crystalline amino acids to the basal diet in proportions equal to the excesses contributed by a test level of soybean meal resulted in a 17.7 percentage unit reduction in the estimate of tryptophan availability (82.3%). When the standard diet was supplemented with amino acids to provide the pattern of excess amino acids found in the corn-gelatin basal diet with added soybean meal, the availability of tryptophan in soybean meal was estimated to be 95.2%. In Exp. 3, the tryptophan availabilities for meat and bone meal, cottonseed meal, corn and sorghum were estimated to be 82.2%, 80.9%, 94.0% and 86.4%, respectively. The diets used in this experiment were supplemented to contain excesses of individual amino acids in the same proportions as found in the basal diet, with the test feed ingredient added as a source of tryptophan. In these experiments the tryptophan content of the various feedstuffs was measured by ion-exchange liquid chromatography following alkaline hydrolysis.

¹ This research was supported by a grant from Ajinomoto Co., Inc., Tokyo, Japan.

² Dept. of Anim. Sci. Part of thesis submitted to the Graduate College, Univ. of Illinois for the M.S. degree.

³ Reprint requests should be addressed to this author at 318 Mumford Hall, 1301 W. Gregory Drive, Urbana, IL 61801.

⁴ Dept. of Anim. Sci.

⁵ The assistance of Scott Williamson, Howard Cook, Dale Alexander, Ron Brewer and Steve Heffernan with diet preparation and animal care and of Miss Julie Thode with manuscript typing is gratefully acknowledged.

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