by Charles A. Manire, Howard L. Rhinehart, Debborah E. Colbert, & David R. Smith
In most species of mammals, a rise in serum creatinine concentrations signals renal failure. This study was initiated to determine the cause of elevations in serum creatinine concentrations that have been observed in rehabilitated West Indian manatees following their return to the wild. During the study (Permit # MA001145-0), routine serum chemistries, blood cell counts, and urinalyses as well as serum creatine kinase and urinary creatinine were monitored. Two captive manatees were utilized to determine the effects of partial fasting, short-term total fasting, simulated transport, diet change from a captive diet to a wild diet, and salinity changes. The most dramatic changes in both serum and urinary creatinine occurred during the partial fasting and short-term total fasting experiments. A diet reduced by 80% for two weeks led to an almost immediate increase in both serum and urinary creatinine concentrations that both returned to normal after one week back on their usual diets. Four days of total fasting also led to an immediate increase that remained elevated for only three days following return to their usual diets. Simulated-transport for six hours did not affect either serum or urinary creatinine in one animal but the other showed a minor increase in serum creatinine that lasted for only a day. Serum lactate dehydrogenase and creatine kinase concentrations were elevated for both manatees, probably as a result of muscle cell damage from being out of the water. Initial results indicate that creatinine elevations are unlikely with both diet change and salinity change. It is suggested that the serum and urinary creatinine elevations are probably due to either protein or fat metabolism that takes place during limited food intake and the manatee kidney is incapable of clearing it as rapidly as it is produced.