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Optimizing the Pattern of Essential Amino Acids as the Sole Source of Dietary Nitrogen Supports Near-Maximal Growth in Kittens^1,2,3,

Timothy P. Taylor^*, James G. Morris^*, Neil H. Willits and Quinton R. Rogers^*,4

^* Department of Molecular Biosciences Department of Statistics, University of California, Davis, CA 95616

Most experiments conducted to determine the optimal essential amino acid (EAA) nitrogen to total nitrogen (E:T) ratio in rats, chicks and other species have shown that weight gain and nitrogen retention are optimal when the ratio is between 0.5 and 0.65. Two experiments were conducted to determine if weight gains of kittens fed EAA as a sole source of dietary nitrogen were equivalent to those of kittens fed a control diet that contained equal amounts of EAA and dispensable amino acids (DAA). In the first experiment, kittens fed diets that contained only EAA lost weight. Amino acid analysis of plasma showed that the concentration of methionine was 9.1 times that of controls, supporting the premise that the weight loss that occurred was the result of an adverse effect of excess methionine. Also, plasma threonine and arginine were elevated whereas proline and asparagine were very low. In the second experiment, feeding lower concentrations of methionine and arginine in a diet containing only EAA resulted in weight gains and nitrogen retention that were not significantly different from results for kittens fed the control diet (E:T ratio = 0.5). The addition of proline and asparagine to this EAA diet or their removal from the control diet did not improve or reduce weight gain or nitrogen retention. It is concluded that the decreased weight gain found in kittens (and probably other species) fed only EAA is the result of an adverse effect of excesses of methionine and possibly other EAA, and not the inability to synthesize DAA. If excesses of certain EAA are avoided, near-maximal weight gain can be achieved without any DAA in the diet.

KEY WORDS: • essential amino acids • dispensable amino acids • feline • kittens

¹ Supported by WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds, UK.

² Presented in part at Experimental Biology 94, April 24–28, 1994, Anaheim, CA [Taylor, T., Morris, J. G. & Rogers, Q. R. (1994) Essential amino acids without dispensable amino acids support normal weight gain in kittens. FASEB J. 8: A545 (abs. 3157)].

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 correspondance and reprint requests should be addressed.

Manuscript received 8 September 1995. Revision accepted 30 May 1996.