Abstract

Hematology and serum chemistry are used to help diagnose disease in marine mammals in rehabilitation and to assess the health of wild populations. In many instances, however, lack of appropriate reference intervals makes interpretation challenging: it is often difficult to sample suitable reference populations and reference intervals are not always calculated in a consistent manner. Our objectives were to generate reference ranges from wild caught and stranded harbor seals (Phoca vitulina) in California, assess the utility of reference ranges from weaned wild pups for evaluating prognosis of stranded newborn pups, and explore the effects of physiological variables on wild pup blood parameters.

Blood was sampled from wild caught and stranded harbor seals pups and a suite of hematology and serum chemistry parameters were determined using automated blood and serum analyzers. Differential white cells were counted manually. Reference ranges (95^th percentiles) and 90% confidence intervals were calculated using a nonparametric bootstrap analysis as recommended by the International Federation of Clinical Chemistry.³ Generalized linear models were used to evaluate the effects of body condition and date of capture.

At admission, a number of the rehabilitated harbor seal pups exhibited values outside the wild weaned pup reference ranges, although there were no clear differences at admission between values from those pups that survived rehabilitation and those that died (Figures 1a and 1b). Deviations from reference ranges were consistent with previously reported differences in mean blood values between wild and rehabilitated pups.² At release, some parameters in captive seals were closer to the wild weaned pup reference values with some notable exceptions: a high percentage of pups at release exhibited levels of platelets, triglycerides, phosphorus, albumin and sorbitol dehydrogenase (SDH) that were greater than the upper threshold for the wild pups. Increases in triglycerides and albumin likely reflect improvement in nutritional status through rehabilitation, while increases in phosphorous could also be a consequence of active bone growth or dietary influences. Reasons for the increase in SDH are unclear, and should be explored as this enzyme may be a useful marker of hepatic changes.¹ Immediately prior to death, a number of pups in rehabilitation exhibited glucose, sodium, and chloride levels below the lower threshold for weaned pups and had leucocyte, neutrophil and band counts above the upper threshold (Figures 2a and 2b). Among the wild pups, monocytes, eosinophils, basophils, hemoglobin, mean cell hemoglobin concentration and creatinine increased significantly with age, while alkaline phosphatase, creatinine kinase, iron, and sodium decreased with age. These pups were sampled one to six weeks after weaning, and these changes may be associated with switching prey⁴ and acquiring parasites.

These changes in blood parameters with age and the lack of differences in values at admission between pups that lived or died through rehabilitation, despite changes detected later in sick animals prior to death, suggest that the value of immediate handling for hematological assessment of malnourished neonates should be weighed against the stress of handling and risk of infection at venipuncture sites in immunocompromised animals.

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Figure 1a. Percentage of pups with blood values at admission to rehabilitation that were below the lower threshold (a) and above the upper threshold (b) for wild weaned pups. The lines between points are to aid visibility and do not imply connections between points.

Figure 1b. Percentage of pups with blood values at admission to rehabilitation that were below the lower threshold (a) and above the upper threshold (b) for wild weaned pups. The lines between points are to aid visibility and do not imply connections between points.

Figure 2a. Percentage of pups with blood values at release or time of death that were below the lower threshold (a) and above the upper threshold (b) for wild weaned pups. The lines between points are to aid visibility and do not imply connections between points.

Figure 2b. Percentage of pups with blood values at release or time of death that were below the lower threshold (a) and above the upper threshold (b) for wild weaned pups. The lines between points are to aid visibility and do not imply connections between points.

 References

1.  Fauquier D.A., J.A.K Mazet, F.M.D. Gulland, T.R. Spraker, and M.M. Christopher. 2008. Distribution of tissue enzymes in three species of pinnipeds. J Zoo Wildl Med 39: 1-5.

2.  Lander M.E, J.T. Harvey, and F.M.D. Gulland. 2003. Hematology and serum chemistry comparisons between free-ranging and rehabilitated harbor seal (Phoca vitulina richardsi) pups. J Wildl Dis 39: 600-609.

3.  Solberg H.E. 2004. The IFCC recommendation on estimation of reference intervals. The RefVal program. Clin Chem Lab Med 42: 710-714.

4.  Thompson P. M., D. J. Tollit, H.M. Corpe, R.J. Reid, and H.M. Ross. 1997. Changes in haematological parameters in relation to prey switching in a wild population of harbour seals. Functional Ecol 11: 743-750.