Abstract

At most institutions, penguins are handled for routine health monitoring at least annually enabling the establishment of normal hematologic reference ranges. Handling or blood collection from molting penguins has been discouraged due to the belief that the already highly stressed birds would be put at significant health risk. Because of this taboo, normal reference ranges for the molt period are often lacking. The ability to distinguish hematologic changes due to molt verses those associated with clinical disease is important. This study describes the hematology and plasma chemistry differences between molting and non-molting birds.

Five randomly chosen penguins of each sex were utilized in this study to examine the hematologic changes associated with molting. Each bird was weighed, examined and blood sampled at seven points: 1) baseline (non-molting) period (one to two months prior to molt); 2) pre-molt, approximately seven days prior to the start of feather dropping (determined subjectively by observing an increase in appetite, increase in body weight and swelling of the wings); 3) molt, the first day that feathers started dropping; 4) seven days into the molt; 5) end of molt, the day all feathers had been replaced; 6) five days post end of molt and 7) post study (one to four months after the end of the last birds molt). All penguins were manually restrained and approximately 10ml of blood was collected from the jugular vein and placed into micro EDTA and sodium heparin tubes. A spun hematocrit, automated red blood cell count, white blood cell count via eosinophil Unopette, and a complete plasma chemistry panel were recorded. The remaining plasma and the buffy coat were stored for future catecholamine and immune function analysis.

A second sampling was conducted to rule out any experimentally induced significant changes in hematologic parameters. Five penguins (two from the previous study and three additional birds) underwent five blood draws outside of the molting season but mimicking the sampling timing employed in the original study. Repeated measures analysis of variance was used to evaluate changes within each bird.

Throughout the study behavior and appetite remained normal eliminating previous concerns over handling penguins during molt. No statistical differences in blood parameters were detected between the sexes and therefore all birds were evaluated together. The results of the molting study show a statistically significant decrease from baseline in spun hematocrit (Hct) and red blood cell count (RBC), with no concurrent decrease in total protein, globulin, albumin or electrolytes. No other blood parameters measured showed biologically significant changes during the molt cycle. At the post baseline sampling time point both hematocrit and RBC values had begun to return to pre-baseline levels but most birds had not yet fully recovered.

Anemia is an absolute decrease in the hematocrit, hemoglobin concentration, and red blood cell count, and can be caused by blood loss, red blood cell destruction or decreased red blood cell production. Relative anemia may occur when the plasma volume is expanded. Anemia due to experimentally induced blood loss was considered and subsequently ruled out as the results of our follow-up control study showed no statistically significant changes in Hct or RBC counts indicating that these changes were truly associated with molt.

In this study RBC destruction is unlikely as all 10 birds were healthy throughout the study, showed no sign of blood-borne parasites and recovered normally after the molt. The molt-related anemia was most likely due to decreased RBC production associated with increased metabolic demands related to feather production combined with the shorter lifespan of avian RBCs. Further sample analysis will focus on stress hormones and lymphocyte subsets to evaluate stress and immune function during the molt.

Acknowledgements

We wish to thank the penguin husbandry team for their support with animal care and handling during blood collection, Amy DelMonaco for hematology analysis and Pfizer Analytical Laboratory for plasma chemistry analysis.