Optimizing Dietary Amino Acid Patterns at Various Levels of Crude Protein for Cats

Abstract

EXPANDED ABSTRACT Experiments with rats (Heger 1990, Stucki and Harper 1962), chicks (Bedford and Summers 1985, Stucki and Harper 1961), turkeys (Bedford and Summers 1988) and pigs (Wang and Fuller 1989) have shown optimal growth rates when the dietary essential amino acid (EAA) 3 nitrogen to total nitrogen (E:T) ratios were between 0.4 and 0.65. It has been consistently found that diets containing only EAA (E:T 5 1.0) yield poor growth rates. Taylor et al. (1996) showed that in kittens fed diets that contain EAA as the sole source of nitrogen [E:T 5 1.0, with the EAA pattern proportionate to the NRC requirements (NRC 1986)], weight loss results. Plasma amino acid concentrations of methionine (and possibly arginine) suggested toxicities of these amino acids. Also, marked depressions in the concentrations of proline and asparagine suggested that these amino acids might be conditionally essential. A near-maximal growth rate for the group receiving all EAA (E:T 5 1.0) was achieved when methionine and arginine were limited to not more than 2.25 times the NRC requirements. No response was obtained with proline and/or asparagine supplementation to the all-EAA diet or when these two amino acids were removed from the control diet. Thus asparagine and proline are clearly dispensable under all conditions tested thus far. These results suggest that the poor growth rates recorded in other species given only EAA (E:T 5 1.0) diets are the result of an intolerance of one or more EAA, rather than a metabolic inability of animals to synthesize dispensable amino acids (DAA) at a rate fast enough for rapid growth, as previously suggested by Harper (1974). Here we report the results of weight gains of kittens fed a wide range of crude protein (CP) levels at various E:T ratios in which excesses of essential amino acids that depress weight gains were avoided. Materials and methods. A control purified diet (CD) was