Effect of Dietary Nitrogen on Nutritional and Metabolic Responses of Kittens Fed Graded Levels of Methionine

Abstract

The essential amino acid requirements of several species are affected by the level of dietary nitrogen. In chicks, pigs and rats, individual essential amino acid requirements are positively correlated with the level of dietary nitrogen. Preliminary experiments indicated that this may not be true for the kitten. Growth and nitrogen retention were used to examine the nature of this response in kittens. A comprehensive set of dose response curves were completed using six latin squares. Each square represented one of the following concentrations of dietary methionine3: 0.15, 0.25, 0.35, 0.45, 0.60 or 0.90% and four concentrations of dietary nitrogen: 15, 20, 30 and 50% crude protein. Plasma amino acid concentrations and selected hor mone concentrations (insulin/glucose, cortisol, somatomedin C, T3 and T4) were also measured. When methionine was limiting, increasing dietary nitrogen did not produce an amino acid imbalance, but rather increased weight gains and nitrogen retention in kit tens. The methionine requirement of the kitten was not positively correlated with the level of dietary ni trogen, but instead was similar for each level of dietary nitrogen tested. Plasma methionine concentrations increased with increasing dietary methionine. At di etary methionine concentrations above the require ment of the kitten (0.40%) (2), plasma methionine de creased with increasing dietary nitrogen. At 0.25 and 0.45% dietary methionine, insulin/glucose ratios and cortisol and somatomedin C concentrations were not significantly different between the levels of dietary ni trogen. At 0.25 and 0.45% dietary methionine, total T3 and T4 concentrations increased significantly (P < 0.05) as dietary nitrogen increased. In conclusion, the methionine requirement of kit tens is not positively correlated with the level of di etary nitrogen as it is in other species, but rather it is similar for each level of dietary nitrogen tested. Weight gains and nitrogen retentions increased in kittens fed diets limiting in methionine as dietary nitrogen in creased. The mechanism by which increasing dietary nitrogen increases weight gains and nitrogen reten tions of kittens when methionine is limiting is not yet clear.