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Somatotropin Enhances the Rate of Amino Acid Deposition but Has Minimal Impact on Amino Acid Balance in Growing Pigs^1,2,3,

U.S. Department of Agriculture-Agricultural Research Service, Beltsville, MD 20705 ^* Bunge Meal Industries, N.S.W. 2646 Australia Heartland Lysine, Inc., Chicago, IL 60631

This experiment was conducted to establish the influence of porcine somatotropin on tissue distribution and deposition rates of amino acids in growing pigs. Barrows were treated daily with buffer or porcine somatotropin (100 µmg/kg body wt) when they weighed between 30 and 64 kg (eight pigs/group). Pigs were restrictively fed so that the average food intake was 1.86 kg/d. The corn-soybean meal-skim milk-based diet contained 18% crude protein and 1.2% lysine, and was designed to meet muscle amino acid ratio profile with respect to lysine as the first limiting amino acid for growth. Tissue levels of eighteen amino acids were determined on lyophilized samples that were appropriately hydrolyzed and analyzed by HPLC. The concentrations (mg/g dry wt) of all amino acids were greater in carcass, skin, head and empty body of porcine somatotropin-treated pigs; amino acid concentration in viscera was not influenced by porcine somatotropin. However, when the concentration of each amino acid was expressed on a per unit protein basis, the amino acid profiles of control and porcine somatotropin-treated pigs were quite similar. The average deposition rate of each amino acid was increased 67% by porcine somatotropin. When the deposition of each amino acid was calculated in relation to lysine, however, the pattern of amino acid utilization for growth was similar for control and porcine somatotropin-treated pigs; exceptions were arginine, glycine and tryptophan. The ratio of indispensable to dispensable amino acids that were deposited was also similar for control and porcine somatotropin-treated pigs. These data indicate that the synthesis rate of individual proteins can be influenced by porcine somatotropin, but the balance of amino acids remains largely unaffected, suggesting that the changes in protein and amino acid metabolism elicited by porcine somatotropin are consistent with normal growth processes.

KEY WORDS: • protein metabolism • growth hormone • somatotropin • amino acids • pigs

¹ Presented in part at Experimental Biology 93, March 28–April 1, 1993, New Orleans, LA [Caperna, T. J., Campbell, R. G., Ballard, M. & Steele, N. C. (1993) Porcine somatotropin (pST) alters rate of amino acid (AA) deposition but not tissue AA profile. FASEB J. 7:A603 (abs. 3491)] and at the 1994 Maryland Nutrition Conference, March 24–25, 1994, Baltimore, MD [Caperna, T. J., Steele, N. C., Campbell, R. G. & Ballard, M.R.M. (1994) Influence of somatotropin on collagen and amino acid metabolism in pigs. Proc. 1994 MD Nutr. Conf. pp. 92–100].

² Mention of trade name, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture or imply its approval to the exclusion of other products or vendors that also may be suitable.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

⁵ Current address: JEFO USA, Inc., 1260 Pheasant Ridge Drive, Lake Zurich, IL 60047.

Manuscript received 8 September 1994. Revision accepted 1 March 1995.