Normal rabbit urine varies in colour from yellow to orange, brown or red depending on nutrition and hydration status and may be influenced by medication.
Rabbit urine always contains a certain amount of sediments. This is absolutely normal, the system of rabbits works this way to excrete the too much of calcium in their body.
The Color of Urine
Healthy rabbits excrete excess calcium salts via the renal system, and this can give the urine a chalky or opaque appearance. The urine will often dry to a white, chalky residue. Unless the residue is thick, pasty, and the color of mustard powder, this is normal, and should not be considered "sludge."
Normal rabbit urine is usually pale yellow in color, but upon exposure to the atmosphere, compounds in the urine may oxidize to darker yellow, orange, red, or even dark brown. This isn't unusual, and--by itself--is not necessarily a sign of a health problem. Blood in the urine, unless it is from a hemorraghing uterus or very serious problem, is usually not readily visible to the naked eye. Test strips are available at most pharmacies that will tell you whether there is blood in the urine or not, but your vet is the best judge of whether your bunny's urine is normal.
Urine that is very dark immediately when it emerges may indicate that the bunny is dehydrated, and should receive more water, either by mouth or--in more serious cases--via administration of subcutaneous Lactated Ringer Solution.
Different color of urine produced by healthy rabbits. The red color is caused by the oxidation of plant pigments.
The absence of sediments in the urine is indicative of renal failure.
A thick paste that becomes a solid millimeter thick “cake” when drying.
Sludge can be treated via a non-invasive procedure. An effective way of washing the bladder without use of catheter, is the administration of subcutaneous fluids, followed by a diuretic drug like furosemide by your vet. One time is usually enough, it can be repeated in the next 24 hours.
Another way is washing the bladder after introduction of a catheter. The procedure is done on an anesthesized rabbit. Since the procedure is accompanied by pain, the rabbit needs to be given pain relief medication. A stone need to be removed surgically.
Calcium and the formation of stones does not relate to the calcium in the diet only. There is much more involved, that we do not understand yet. One cause of uroliths (stone) may be increased pH of the urine, for some reason or another (e.g. diet, presence of bacteria). The increased urine pH favors the development of bacteria and UTI. Bacteria in the bladder will, on the other hand, start to excrete waste (ammonium) and an enzyme, urease that will break down the urea; both will increases the pH of the urine. An increased pH accelerates the precipitation of struvite crystal (struvite = magnesium, ammonium, and phosphate). Struvite stones develop only in the presence of an alkaline pH.
Commonly found bacteria are E. coli, Proteus sp and Staphylococcus sp, rarely true anaerobic bacteria are found. The presence of bacteria can be easily checked by sending a sample of urine for bacterial culture (urine is normally sterile). One can also keep the removed urolith, open it, and use the central part for bacterial culture or have the stone examined for the crystals composition. Indeed, some bacteria are associated with a particular type (e.g. Staphylococcus is associated to struvite stones).
A 1.9 cm bladder stone Photo:
Hematuria (urine with blood traces)
Thick urine, the presence of a bladder stone, a bladder or kidney infection, or infection of the urinary or reproductive organs are usually accompanied by the presence of blood spots in the urine.
Some dried blood in the urine circle
Heavy blood loss, caused by a cystitis in a female rabbit
Another possible cause?
Sometimes rabbits are often kept in small cages with no or little opportunity to exercise and this has also been claimed to be a predisposing factor. Age and breed does not seem to be a factor for urine issues.