Animal Producing Most Concentrated Urine

Which animal produces the most concentrated urine?

Correct Answer: Dog

Among the options, the dog produces the most concentrated urine. This is because dogs have 100% juxtamedullary (JM) nephrons — nephrons with very long loops of Henle that extend deep into the renal medulla.

Why Long Loops of Henle = Concentrated Urine

The countercurrent multiplier system (loop of Henle) and countercurrent exchanger (vasa recta) create a high osmotic gradient in the renal medulla. The longer the loop of Henle, the higher the medullary osmotic gradient, and thus the more concentrated the urine that can be produced when ADH acts on the collecting duct.

Percentage of Juxtamedullary Nephrons by Species

• Beaver: 0% JM nephrons → produces the most dilute urine (aquatic animal, no need to conserve water)
• Pig: 3% JM nephrons
• Human: 14% JM nephrons
• Cat & Dog: 100% JM nephrons → produce the most concentrated urine

Urine Characteristics of Horse

Interestingly, horse (due to high mucus content and calcium carbonate crystals), and mucus is found in the urine of both horses and fowl — but this does not mean the urine is concentrated.