Dietary crude protein concentration does not affect the leucine requirement of growing dogs

The objective of the present study was to examine the interaction between g raded levels of leucine and dietary crude protein. Dose-response curves wer e generated using four 3 x 3 Latin squares (two dogs/square). Each square r epresented one of two concentrations of crude protein (140 or 280 g/kg diet ) and one of two combinations of three concentrations of leucine (5.0, 7.0 and 9.0 g/kg diet or 9.0, 11 and 13 g/kg diet). An additional experiment wa s performed by feeding crude protein at 210 g/kg diet with either 7.0 or 11 g leucine/kg diet. Weight gain, food intake, nitrogen retention, plasma al bumin and plasma amino acids were measured. The requirement was determined to be the minimum leucine concentration required to maximize weight gain an d nitrogen retention. For 8-14-week-old male Beagle dogs, 140 g crude prote in/kg diet in a diet containing 18 kJ metabolizable energy/g does not appea r to support maximal growth. The leucine requirement was not affected by do ubling the dietary crude protein level from 140 to 280 g/kg diet. From thes e results, the leucine requirement of 8-14-week-old Beagle dogs appears to be 11 g leucine/kg diet independent of the level of dietary crude protein, whereas dogs over 14 weeks require only 7 g leucine/kg diet for maximal nit rogen retention.