Abstract

Harbor seals (Phoca vitulina richardsi) are commonly treated as rehabilitation patients on the Pacific Coast of North America, most frequently as neonates and pups. These patients often have elevations in their total bilirubin or other liver values on serum chemistry, and further diagnostics may be required to differentiate physiologic hyperbilirubinemia of neonates¹ versus true liver pathology, such as congenital portovascular anomalies. Measurement of serum bile acid concentration is a good indicator of hepatobiliary function and portal blood flow. Measurement of Protein C, a Vitamin-K dependent protein synthesized in the liver, can also aid in diagnosing liver disease and assessing portal blood flow non-invasively.² The objective of this prospective pilot study was to establish normal values for bile acids (fasted [FBA] and 2-hour post-prandial [PPBA]) and Protein C in harbor seal pups undergoing rehabilitation. Venous blood was obtained from 14 harbor seals at the Vancouver Aquarium Marine Mammal Rescue Centre, ranging from 7–16 weeks of age. Patients included in the study were those deemed healthy aside from malnutrition and maternal separation, which were not on any systemic medications for 6 weeks prior to blood sampling, and had not received any antibiotics for more than 7 days. Bile acid values were analyzed for mean, median, and standard deviation. ROUT analysis was used to identify outliers in the data, resulting in removal of 4 values. The fasting bile acid values (n=12) were normally distributed, while the 2-hour PPBA (n=12) were not normally distributed (p=0.0004). A comparison of paired samples of the FBA and 2-hour PPBA was performed using Wilcoxen signed-rank test (non-parametric, two-tailed) and showed that the FBA and PPBA were significantly different (p=0.002), with a mean FBA of 8.36 µmol/L (±5.73) and PPBA of 30.64 µmol/L (±10.82); the median difference between pairs was 19.1 µmol/L. Interestingly, the mean values obtained for PPBA in the current study are higher than the normal range for domestic species, demonstrating the need for species-specific reference intervals. Protein C activity was measured using a chromogenic assay (Cornell University, Animal Health Diagnostic Center, Ithaca, NY), in which seal Protein C activity was measured against a human control of 100% Protein C activity. Protein C values (n=12) showed normal Gaussian distribution and no outliers were detected. The mean Protein C activity was 96.67% (±12.03%). These results suggest that Protein C activity is fairly uniform across species (human, domestic animals, and harbor seals), and this assay can be helpful in identifying and differentiating liver pathology in harbor seals. Computed tomography and angiography was also performed with one seal from the normal group to act as a control to aid in diagnosing portosystemic shunts. This pilot study was the first to establish normal mean values in harbor seals for bile acids and Protein C, which will aid clinicians in the diagnosis of hepatobiliary disease in harbor seal pups. Further work is being done to increase the sample size and obtain true reference intervals, and to compare values at different age classes.

Acknowledgements

The authors would like to thank the volunteers and veterinary technicians at the Vancouver Aquarium Marine Mammal Rescue Centre for their tremendous assistance, especially Lindsaye Akhurst, Jenelle Leedam, Shanie Fradette, Belinda To, and Talia Smith.

* Presenting author
+ Student presenter

Literature Cited

1.  Dierauf LA, Dougherty SA, Baker B. Neonatal hyperbilirubinemia in harbor seals (Phoca vitulina richardsi). 1984. The Journal of Zoo Animal Medicine. 15(2):55–59.

2.  Toulza O, Center SA, Brooks MB, Erb HN, Warner KL, Deal W. 2006. Evaluation of plasma protein C activity for detection of hepatobiliary disease and portosystemic shunting in dogs. Journal of the American Veterinary Medical Association. 229(11):1761–1771.