Rabbit urinary system — unipapillate kidneys and calcium-rich urine
Overview of the rabbit urinary tract — kidneys draining through a single renal papilla, a distinctive calcium pathway that routes surplus dietary calcium out through the urine, and naturally alkaline, often cloudy urine.
General educational reference only — not clinical or veterinary advice. Anatomy varies between individual animals; consult a licensed veterinarian for any health concern.
Unipapillate kidneys
The rabbit's two bean-shaped kidneys lie against the roof of the abdomen, the right somewhat ahead of the left. Each is unipapillate: all of its collecting ducts converge on a single renal papilla draining into a single calyx and then the ureter — a notably simple internal layout that has made the rabbit kidney a standard subject in physiology teaching and research. The ureters carry urine to the bladder, which empties through the urethra.
A different calcium pathway
Most mammals regulate calcium at the gut, absorbing roughly what the body needs and discarding the excess in bile and feces. Rabbits absorb dietary calcium efficiently regardless of need and excrete the surplus through the kidneys instead, so the fraction of calcium leaving in urine is many times higher than in most other mammals. That surplus is voided as fine calcium carbonate sediment, which is why normal rabbit urine is often visibly cloudy or creamy rather than clear.
Bladder and the character of urine
The bladder is large and thin-walled. As in other herbivores whose metabolism yields alkaline waste, rabbit urine is normally alkaline rather than acidic. Its color spans a wide normal range — pale yellow through amber to orange or rusty red — because plant pigments from the diet, and porphyrin pigments produced by the rabbit itself, pass out in the urine; the depth of color varies with diet and hydration.
