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

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.