Abstract

Manatees in rehabilitation centers are typically fed commercially grown lettuces in addition to a very limited amount of native forages. These commercially grown feedstuffs contain from 2–6 times the caloric density of seagrasses and are very digestible with low fiber content.¹ While a highly digestible, energy-rich food is desirable for critically ill animals, prolonged feeding of such a diet can lead to other metabolic conditions.^1,2 Diabetes mellitus has been diagnosed in a rehabilitated manatee that was released and did not survive, with other clinical cases suspected (Ball 2016, unpublished data). Fructosamine reflects blood glucose concentrations over a 2–3 week time period. Elevations reflect persistent hyperglycemia and are strong indicators of type 2 diabetes.

Serum and/or plasma samples from twenty-five wild manatees from the Crystal River health assessments during the capture seasons December through February 2017 and December through February 2018 had fructosamine levels evaluated using an IDEXX Catalyst™ biochemistry machine at ZooTampa’s veterinary clinical pathology laboratory. Standard blood collection methods were applied and all samples were separated at the capture site and refrigerated until they were placed in a -80°C freezer. Mean, median, standard deviation, maximum, and minimum were calculated using untransformed data while 90% confidence intervals were calculated using Box-Cox transformed data and are summarized in Table 1. All statistical tests were conducted with Reference Value Advisor freeware™.

Table 1. Descriptive statistics for fructosamine in wild manatees

In normal horses, mean fructosamine was 248.7 μmol/l with the normal range (mean±2 s.d.) reported as 195.5–301.9 μmol/l,³ which is consistent with the values reported here. Retrospective evaluation of both rehabilitated and long-term captive manatees show several with values significantly over the range reported here for wild manatees. Manatees staying at length in rehabilitation centers or long-term captive manatees with prolonged consumption of a relatively high energy and low fiber diet seem to be at risk of developing elevated levels of fructosamine. This is strongly suggestive of diabetes mellitus, although chronic stressors can also elevate fructosamine. Closer evaluation into the length of time in managed care, feeding alternatives, and even changes in release criteria may all minimize the effects of a prolonged captive diet on wild manatees. Manatees with repeated fructosamine levels over 300 μmol/L should be suspected of developing diabetes mellitus and followed up appropriately.

Acknowledgements

The authors would like to thank Maggie Hunter, USGS, for permission to evaluate these manatee samples and her feedback.

Literature Cited

1.  Siegal-Willott J. 2010. Proximate nutrient analyses of four species of submerged aquatic vegetation consumed by Florida manatee (Trichechus manatus latirostris) compared to romaine lettuce (Lactuca sativa var. longifolia). J Zoo Wildl Med. 41(4):594–602.

2.  Harshaw Lauren. 2012. Evaluation of the nutrition of the Florida manatee (Trichechus manatus latirostris). [dissertation] University of Florida.

3.  Knowles EJ. 2014. Plasma fructosamine concentrations in horses with pituitary pars intermedia dysfunction with and without laminitis. Equine Vet J. 46(2):249–51. doi: 10.1111/evj.12090. Epub 2013 Jul 4