Maximal growth occurs at a broad range of essential amino acids to total nitrogen ratios in kittens

Abstract

Kittens fed diets containing 2.0 and 3.0 times (x) the NRC (1986) essential amino acid (EAA) requirement (EAArq) and 210 to 560 g crude protein (CP)/kg diet had growth rates and plasma amino acid patterns that were not significantly different than kittens fed a control diet (CD) containing 1.5 x EAArq and 350 g CP/kg diet. Growth rates of kittens fed diets containing only EAA (with nontoxic levels of arginine and methionine) and 280 to 460 g CP/kg diet were equivalent to those of kittens fed CD. Kittens fed only EAA and 140 and 210 g CP/kg diet had growth rates that were significantly lower than kittens fed CD. Since the growth rate of kittens fed 1.5 x EAArq and 210 g CP/kg diet in a previous experiment was equivalent to kittens fed CD (Taylor et al., 1997), it is suggested that the requirement for CP is higher (up to 280 g CP/kg diet) when only EAA are fed. The higher crude protein requirement appears to be primarily a consequence of the high obligatory nitrogen loss as urea (especially from arginine) incurred in the conversion of nitrogen from EAA to dispensable amino acids in the liver and secondarily because of a slow rate of catabolism of the EAA. A 3-dimensional plot of weight gains vs. CP levels and EAA to total nitrogen (E:T) ratios of kittens shows a broad range of CP levels and E:T ratios that support optimal growth in the kitten. It is suggested that similar patterns would occur in the chick, rat and other species if adverse effects caused by excesses of specific amino acids are avoided.

Protein and amino acid nutrition and metabolism in fish: current knowledge and future needs

“…The lack of control of amino acid catabolism as affected by dietary protein levels is indeed considered to be one major reason for the high protein requirements of fish (Cowey & Walton 1989). This is somewhat comparable to what is found in the carnivorous cat, where the high protein requirement is considered to be a consequence of the high obligatory nitrogen losses incurred in the conversion of nitrogen from indispensable amino acids (IAA) to dispensable amino acids (DAA) in the liver and to a slow rate of catabolism of IAA (Taylor, Morris, Kass & Rogers 1998).…”

Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats

“…Protein quality was controlled across diets by proportionally increasing the protein-supplying ingredients, and all diets were formulated to provide amino acids at an optimal ratio of essential to total amino acids. 20 Apparent digestibility of the protein was approximately 85% (data not shown), although it was lower in the LO diet owing, most likely, to a relative increase in the contribution of endogenous and bacterial proteins to fecal nitrogen. The protein requirement might be expected to be even higher if diets with lesser amounts of one or more essential amino acids, or protein with lower digestibility, were used.…”

Discrepancy between the composition of some commercial cat foods and their package labelling and suitability for meeting nutritional requirements

“…It should be noted, however, that a number of wet foods exceeded the concentration of individual amino acids that were used in those SUL studies. The concentrations of isoleucine (in one wet food), leucine (in one wet food) and histidine (in three wet foods) were greater than the concentrations investigated by Hargrove et al and Taylor et al Possible consequences of such high concentrations of certain amino acids in these commercial cat foods are currently unknown.…”

“…A small number of studies have been performed in cats and kittens in an attempt to determine the SUL for each essential amino acid. However, there have been no reports of acute or chronic toxicity related to feeding certain large quantities of free lysine, phenylalanine or taurine in the kitten or free isoleucine, leucine, threonine, valine or histidine in the cat . It should be noted, however, that a number of wet foods exceeded the concentration of individual amino acids that were used in those SUL studies.…”