The renal excretion of nitrogenous compounds by the duck (Anas platyrhynchos) maintained on freshwater and on hypertonic saline.

The successful adaptation of the duck (Anas platyrhynchos) to a diet containing hypertonic saline as drinking water involves many complex changes in the excretory mechanisms of the bird (Fletcher & Holmes, 1968; Fletcher, Stainer & Holmes, 1967; Holmes, Fletcher & Stewart, 1968; Holmes & Stewart, 1968). These changes include modifications of the renal excretory pattern such that at least part of the increased electrolyte intake of the bird may be excreted via this pathway. The concentrating capacity of the nephron of the bird is limited when compared with that of the mammal, and a considerable portion of the osmotic space in the hypertonic urine produced by the saline-adapted bird is occupied by nitrogenous compounds. The purpose of the present investigation, therefore, was to determine the pattern of excretion of nitrogenous compounds in the urine of the freshwater-adapted and of the saline-adapted duck under conditions of controlled food intake.