Abstract

Two-hundred-twenty-three urine samples were collected during repeated capture-release health assessments from 141 free-ranging bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida, during 1993–2011.^1,2 The urine samples were primarily collected via catheterization (very few were free-catch urine samples), analyzed to determine baseline values for normal biochemical and microscopic variables in dolphin urine and to investigate differences by age and sex. The majority of urinalysis findings were medium yellow colored (83%), clear (65%) urine with a mean urine specific gravity of 1.024 ± 0.009 SD, a predominately acidic pH (mean 6.11 ± 0.445 SD), which is similar to that of other marine mammal species,³ and mild cellularity. Dipstick evaluation for glucose, ketones and nitrites were negative in all samples. While most urine samples (77%) indicated a negative blood dipstick reaction, 23% of samples had variable degrees of positive blood dipstick reactions, which was further confirmed by the microscopic identification of intact red blood cells. This finding is likely associated with the catheterization process and/or genital tract contamination in males and females. Bilirubin was detected as a small amount in 11% and a moderate amount in 1% of urine samples. It is unknown whether dolphins have a low renal threshold for bilirubin similar to dogs.⁴ Protein dipstick evaluation was negative in 22% of samples, but resulted in 1+ to 2+ positive dipstick reactions in 59% of samples, and 3+ to 4+ positive reactions in 19% of samples. Some of these positive protein dipstick reactions likely can be associated with the presence of red blood cells and/or lower urinary tract contamination in males and females; however, the possibility of proteinuria was not further confirmed by sulfosalicylic acid precipitation. Urinary sediment evaluation did not reveal any evidence for urinary tract infection in any of the study animals. Variable numbers of bacteria were observed in 20% of the urine samples; given the polymorphic morphology of the bacterial population and absence of inflammation in these samples, these bacteria were considered contaminants from the lower urinary tract or the environment. In addition, fifty urine samples were submitted for culture, of which 18 had microscopically observed bacteria, but no culture samples resulted in any growth. Few to many calcium oxalate dihydrate crystals were observed in 8% of samples. This finding is consistent with a low prevalence of calcium oxalate dihydrate crystals in dog urine,⁴ and in contrast to recent reports that described magnesium ammonium phosphate calculi in a wild female dolphin and urate nephrolithiasis in captive bottlenose dolphins^5-7. Low numbers of hyaline casts were present in 10% of urine samples. Hyaline casts have been associated with exercise in mammals,⁴ and are likely consistent with exertion during capture. There were no significant differences in biochemical and microscopic parameters between adult females, adult males and immature animals. Our urinalysis dataset provides urinalysis baseline values indicative of a healthy wild dolphin population, providing urinalysis reference values as a valuable diagnostic tool for the medical care of dolphins undergoing rehabilitation or in human care.

Acknowledgments

The authors wish to thank veterinarians, biologists, volunteers, organizations and laboratories involved with the Sarasota Dolphin Research Program's examinations and sampling of dolphins over the last two decades. Funding has been provided by Dolphin Quest, NOAA Fisheries, the Georgia Aquarium, and Disney for sample collection. This research was conducted under a series of NMFS scientific research permits.

References

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