Abstract

An assay of hematologic parameters is an important component of a complete health examination, and has obvious value in the assessment of patients or the reassessment of post-treatment patients. In Sphenisciforms published reference ranges for hematocrit and erythrocyte counts are not well documented. Several years of blood sampling from the African Black Footed penguins (Spheniscus demersus) at Mystic Aquarium and interpretation of their hemograms have documented seasonal hematologic variations. Hematocrit especially has been noted to decline without evidence of injury or disease and to increase subsequently in the absence of any treatment. Previous studies conducted on various avian species examined the effects of age, sex, time of day, breeding and physiologic status on several blood parameters but hematocrit variation has received little attention in hematological studies of penguins.^{2,5,6,8,9,15,16,25,27}

This study was designed to examine hematocrit variations in relation to the physiological status of the African Black Footed penguins and, specifically, to determine how molt influences that parameter. We hypothesize that molt imposes hormonal, immunological and energetic challenges that result in a hematocrit decrease in otherwise healthy birds.^1,18 239 samples were collected from healthy birds in the period 1995-2005. Most (222) were routinely scheduled samplings and only 17 were collected during the molt. All birds were sampled from the jugular vein, usually in early morning. Hematocrit was determined as the percentage of packed red cell volume to total column height (plasma + packed red cell volume). All hematocrit measurements were made within 3 hours of sampling. One Way Analysis of Variance (ANOVA) was used for comparison of the hematocrit in molting versus non molting birds. Although the sample size in this study was limited, the results showed a statistically significant difference (p<0.05) in hematocrit between molting and non molting birds. The hematocrit of molting birds averaged approximately 7.4% less than the hematocrit of non molting birds, thus supporting our hypothesis.

A number of hypotheses have been advanced to explain this reduction in hematocrit during the molt. Since hematocrit is only a measurement of relative volume, it can vary because of changes in the size and/or numbers of hemocytes or in plasma volume. Hematocrit may decline because of (1) a reduction in erythropoiesis secondary to nutritional and energetic imbalances undergone during the molt including some degree of fasting, potentially leading to iron deprivation.^1,11,23,29 Previous studies on Humboldt penguins (Spheniscus humboldti) show that molting is associated with low concentrations of sex steroid hormones and a drastic increase and subsequent decrease of thyroid hormones. These hormonal changes may influence hematological values.^{3,4,7,10,12,13,14,17,19,20,21,22,24,26,28}

A second (2) possible explanation for the decrease in hematocrit is hemodilution, an increase in plasma volume as an osmotic adjustment in response to the extensive vascularization of growing feathers without an accompanying increase in erythrocyte population or size.^6,29,30

These hypotheses are not mutually exclusive and therefore a combination of patterns may be observed. Results of this pilot study have confirmed for us the need to initiate a more complex investigation to determine the cause(s) of the molt associated hematocrit decline.

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