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Health & welfare management

Effects of capture on haematological values and plasma cortisol levels of free-range koalas (Phascolarctos cinereus)

Hajduk, P, Copland, MD & Schultz, DA 1992, Journal of Wildlife Diseases, vol. 28, no. 3, pp. 502-506.

Eight wild koalas were captured on Kangaroo Island, South Australia, placed in transport boxes, and then transported to the Adelaide Zoo by ferry and road. Blood samples were collected from these koalas at the time of their capture, and subsequently six hours, 24 hours and seven days following their capture. Significant differences in the following properties were observed between the samples: erythrocyte (red blood cell) number, haemoglobin concentration, packed cell volume, mean cell volumes, numbers of the white blood cell types leukocytes, neutrophils and lymphocytes, as well as lymphocyte: neutrophil ratio.  No significant differences could be found between sampling periods for the following properties: number of the white blood cell types monocytes and eosinophils, and plasma cortisol levels.

  Red blood cell counts were observed to generally decrease with time after capture. Exertion and excitement can cause the spleen to contract, resulting in stored erythrocytes being released into the blood. This is thought to be the reason for the increased red blood cell count recorded in the captured koalas. Neutrophil numbers increased considerably six hours after capture, but declined 24 hours and seven days later, although at seven days following capture they were still higher than at the time of capture. Lymphocyte numbers were lowest six hours after capture, but then progressively increased.

  Blood cortisol level is a common and widely accepted indicator of stress in animals, as this hormone is released as a result of stress. The mean level of blood cortisol did not significantly change between sample periods. This is surprising, as capture is likely to be both frightening and stressful for koalas. There was, however, considerable variation within individual koalas, with some showing elevated levels at capture and others showing no detectable response. It is thought that the small sample size was responsible for the lack of statistical significance.

  Measuring haematological values (data pertaining to blood or blood diseases) is useful to monitor disease and general health in koalas and other animals. As exercise and stress is known to influence haematological values, as demonstrated in this study, the potential influence of any animal handling should be considered before interpreting haematological data. The findings of this study indicate that capture has a substantial physiological effect on koalas and that the time after capture a blood sample is taken is an important consideration when assessing the haematology of koalas.


Summarised by Alexander Hendry


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