Steven R. Brown1, DVM; Mike Glenn2, GED Curator of
Mammals; Susan R. Libra1, DVM
The presence of perivulvar uroliths in domestic animals may indicate a pathological process occurring in either the urethra, bladder, ureter or kidney, and warrants further examination of those structures. During an unrelated anesthetic procedure in December 1992 perivulvar uroliths were discovered on Sitka, an Alaska sea otter at Oregon Coast Aquarium.
Sitka, a 25kg female sea otter born in February or March 1989, was rescued from Valdez, Alaska during the oil spill crisis. There is no record of her condition at the time of rescue. She initially resided at Vancouver Aquarium, Vancouver, B.C., Canada. She was then transferred to Oregon Coast Aquarium in April 1992 where she lives in an exhibit with two other sea otters (one male, one female). With the exception of one abscessed tooth and one matted coat, this collection of sea otters has been healthy.
Sitka was anesthetized in June, July, October and December 1992 for hand grooming of a matted coat problem which neither of the two other otters in the exhibit developed. Blood, skin biopsy and fecal samples were taken during the course of Sitka's treatment for laboratory evaluation. Also, in June 1992 one mite was found near her nasal passages and collected for identification.
At the December 1992 treatment Sitka's perivulvar skin folds were retracted and several calculi were found attached to the fur. These had not been observed on Sitka in the exhibit. The calculi were collected for analysis at Baylor College of Medicine, Houston, Texas. Abdominal radiographs were taken and urine was collected by cystocentesis for urinalysis.
Sitka has not been examined under anesthesia since December 1992. No further perivulvar calculi have been observed on her in the exhibit. Other than a stillborn pup in May 1993, she continues to have a good medical history.
Results of the blood analyses during the seven month period give no indication of a significant abnormality when compared to available published normals for sea otters from the CRC Handbook of Marine Mammal Medicine (Table 1). Sitka did have a slightly below normal serum potassium and globulin in June 1992. Since all other physical and chemical parameters were normal and these values did not persist, they do not appear to be significant. Normal ranges for sea otter platelet count, nucleated red blood count, chloride, total bilirubin, GGT, AST, magnesium, and thyroid values are not available to us at this time, so their effect here cannot be evaluated.
The skin biopsy and fecal evaluations showed no abnormalities, as did the abdominal radiographs. The mite was identified as the larval stage of the common nasal mite (Halarachne species), which can cause clinical disease and disability if present in large numbers.
The urinalysis resulted in a urine ph of 7.50. There were zero to one cells of undetermined origin/hpf and zero to three crystals also of undetermined origin/hpf. The urine contained a trace (<30mg/dl) of protein and no bacteria, red blood cells, white blood cells, casts, or sperm (Table 2). The calculi were composed of 65% magnesium ammonium phosphate hexahydrate and 35% ammonium acid urate. No nidus was observed and stone fragments were "found in and around hair ball type material."
The conclusion from this laboratory data is that a non-pathological process was the most likely cause of Sitka's perivulvar uroliths. The other otters in the exhibit, diet, water composition, information from other aquariums, and information on wild sea otters are being looked at to discover clues as to the stimulus for perivulvar urolith formation.
Cody, the male sea otter in the exhibit, did not produce uroliths around his prepuce. His clinical and chemistry status was within normal limits during the period from June to December 1992. Kiana, the other female sea otter in the exhibit, did produce perivulvar uroliths, and also had a clinical and chemistry status within normal limits.
Perivulvar uroliths have been identified at Vancouver Aquarium on both young and old female sea otters. The Seattle Aquarium did not observe uroliths on a 25 year old female sea otter. Point Defiance Zoo and Aquarium also has not observed perivulvar uroliths on their female sea otters. From the observations of Dr. Tom Williams, DVM, wild sea otters have not produced perivulvar uroliths.
Sea otter diets at Oregon Coast Aquarium, Vancouver Aquarium, and of wild sea otters are shown in Table 3. Proximate analysis results are not yet available for comparison. All diets appear to include a variety of mollusks and crustaceans. Vancouver Aquarium, in addition, offers boney fish and echinoderms, more closely approximating the wild otter diet.
Natural sea water is used for sea otter exhibits at Oregon Coast Aquarium, Vancouver Aquarium, Seattle Aquarium, Point Defiance Zoo and Aquarium, and Sea World of San Diego. At Oregon Coast Aquarium the average salinity from April 1992 to December 1992 was 30%, the average water temperature was 52 F, and the water ph averaged 7.60. The exhibit consists of 75,000 gallons of sea water, and ozone is the only form of disinfectant used. The aquarium uses three, high rate eight foot sand filters with a turnover rate of 45 minutes.
Although information from other aquariums is still in the gathering process, observations and data acquired suggest that perivulvar uroliths are interesting incidental and non-pathological deposits that form in some captive sea otters from the chemical interactions between urine and environmental elements within the protective folds of the skin around the vulva. Identification of which specific interactions cause the crystals to form will require a more in-depth investigation of captive and wild sea otter urine and environmental components.
1. Dr. Tom Williams, DVM, Monterey Bay Aquarium, Monterey, CA. Andy Johnson, Curator, Vancouver Aquarium, Vancouver, B.C., CAN.
2. C.J. Casson, Seattle Aquarium, Seattle, WA.
3. Nolan Harvey, Point Defiance Zoo and Aquarium, Tacoma, WA. Tom Reiderson, DVM, Sea World of San Diego, San Diego, CA. Marine Mammals Staff, Oregon Coast Aquarium, Newport, OR.
1. Dierauf, Leslie A. Handbook of Marine Mammal Medicine, CRC Press, Boca Raton, FL, 1990.
2. Tuomi, Pam. "Rehabilitation Notes: Sea Otter Pups (Enhydra lutris)", wildlife Journal Vol.13 No.3.