Abstract

American alligators (Alligator mississippiensis) hatched from eggs collected in the Everglades National Park and raised at Gatorland Zoo were compared with wild alligators taken directly from the Everglades National Park. Nine (9) wild-caught alligators were kept at the University of Florida, College of Veterinary Medicine aquatic animal research laboratory for a 4-month study before return to the park. Fecal examinations were done and blood was collected every 2 weeks from these animals. Serum chemistry, protein electrophoresis, complete blood counts (CBC), and thyroid hormone profiles were determined. Weights and lengths of the animals were also measured. Initial comparisons on the wild-caught to captive-raised animals showed significant differences in several blood values. The wild-caught animals were also found to be anemic when compared to genetically similar control animals. Removal of leeches, feeding the wild-caught animals a high protein diet and providing a sanitary living space resulted in the blood values becoming closer to values for the captive-raised, genetically similar, control animals.

Introduction

Wild alligators in the Everglades National Park have been found to have a poor body condition score when compared to captive controls and wild animals from other areas.¹ The wild-caught animals were also found to be anemic when compared to genetically similar control animals. In order to determine the cause of the anemia and poor body condition, 9 wild Everglades National Park alligators measuring from 1 to 1.6 meters in length were captured. These wild-caught animals were brought to the University of Florida, College of Veterinary Medicine for study. All animals had fecal examinations and blood was collected biweekly for analysis. Serum chemistry values, protein electrophoresis, CBC (complete blood counts) and thyroid hormone levels were measured. Many of the clinical values were significantly different from genetically similar control animals that were hatched from eggs collected in the park but raised at Gatorland Zoo. Feeding the wild-caught animals the same diet as the control animals at Gatorland resulted in blood values that were changing toward values of the captive-raised control animals.

Materials & Methods

Nine (9) alligators were randomly collected at night in the Everglades National Park and returned to the University of Florida, College of Veterinary Medicine for study. The animals were captured the second week of September 1998 and were returned to the Everglades National Park after the final blood collection and measurements were taken on the last week of January 1999. All alligators collected were between 1 and 1.6 meters in length. Size was the only collection criteria because of enclosure constraints present at the university.

The animals were examined upon arrival at the laboratory, weighed, measured for length, and blood was collected to determine baseline values for each animal. Six of the animals were maintained in rectangular enclosures of approximately 300-gallon capacity. One animal was held in a round tank of approximately 700-gallon capacity, and the two smallest animals were held in enclosures of approximately 250-gallon capacity. Fresh water was provided to the animals at all times. Food consisted of horsemeat identical to that in the diets of animals at Gatorland Zoo. A fecal exam was performed after the animals had been in captivity for the first month. Blood was collected every 2 weeks during the experiment and CBC, serum chemistry, thyroid hormone profile, and serum protein electrophoresis was performed on all blood samples. Eight of the animals were released at the termination of the experiment. One animal was retained.

Nine captive-raised animals held at Gatorland Zoo were utilized as controls during the course of the experiment. These animals were hatched from eggs collected from the Everglades National Park and therefore should be genetically similar to the wild-caught animals in the experiment. The captive-raised animals are between 2 and 3 years of age. These animals had blood collected for comparison to the wild-caught animals. All the animals held at Gatorland Zoo had normal growth rates and body condition and were considered normal healthy alligators. The same series of tests were performed on blood from the captive-raised animals as was performed on the wild-caught animals. Routine weights and lengths were also determined for these animals.

Whole blood samples were placed in lithium heparin tubes for CBC and serum separation tubes for all other tests. The serum was stored frozen in lithium heparin tubes until it was analyzed. An average of 5 ml of whole blood was collected from each wild-caught alligator every 2 weeks, and each captive-raised alligator monthly.

Serum chemistry and protein electrophoresis was performed at the University of Florida, College of Veterinary Medicine clinical pathology laboratory for all samples taken. Thyroid hormones were determined at Michigan State University (MSU) by Dr. K. R. Refsal. All serum samples to MSU were shipped frozen. Complete blood counts (CBC) were performed by means of a Coulter counter (model F) at the aquatic animal research laboratory. Descriptive statistics were performed using the SAS software package.

Results (Table 1)

Table 1. Means of clinical values for wild-caught Everglades alligators during first half (wild early) and last half (wild late) of experiment, and captive-reared control animals.

* = Not significantly different between groups during experiment

Table 1 shows selected differences between the captive-raised and wild-caught alligators for the mean values. The "wild early" values were those means taken in the first 8 weeks of the experiment, while the "wild late" values were means taken during the last 8 weeks of the experiment.

Statistically significant differences between captive-raised and wild-caught animals were seen in several clinical values (Table 1). Initially, the wild-caught animals were found to be anemic when compared to the captive-raised, control alligators. Red blood cell indices and packed cell volume began to increase over time but never achieved the levels of the captive-raised animals. Protein electrophoresis values of wild-caught animals were elevated initially in the globulin region when compared to the captive-raised control animals. These values decreased in most animals over the course of the experiment. Liver enzyme and kidney values were not significantly different, although AST and ALT values decreased in the wild-caught animals over the course of the experiment to a level comparable to the captive-raised animals. Thyroid hormone levels were observed to decrease over time in the wild-caught animals, especially for reverse T3 (rT3).

External parasites (leeches) were found on all the wild-caught alligators. Any external parasites were removed when they were found. All wild-caught alligators had leeches and were found positive for Haemogregarina sp. The parasite was present in less than 5% of RBC.

Discussion

The anemia initially present in the wild-caught animals had not completely disappeared by the end of the experiment. Captive-raised control animals still had a higher packed cell volume and RBC count. The RBC parasite, Haemagregarina, was still present in all animals at the end of the study period. Leeches are known to be the vector for Haemogregarina sp., but these were removed from wild-caught animals early in the study period. Haemogregarina is considered commensal⁴, but has been found to elevate the eosinophil count on alligators if they are present². Eosinophil counts were elevated for all of the wild-caught animals in the present study. It is also possible that the intervals for blood collection in the wild-caught animals were too short and that the animals did not have enough time to regenerate red cells between blood collections, thus preventing a correction of the anemia. It is further possible that more time was needed to completely resolve the anemia in the wild-caught animals, because of slow metabolic rates. The experiment began in the fall of 1998 and the animals were beginning to enter torpor at the end of the experiment. Monthly blood collection in the future would possibly be a more desirable collection interval on smaller animals in order to prevent experimentally induced anemia.

Total serum proteins were not significantly different between captive-raised animals and wild-caught at the end of the experiment. Serum protein electrophoresis levels in the globulin region of the electrophoretogram for wild-caught alligators decreased over time. This could be due to a reduction in stress, lower antigen load from the type of food given the animals or reduction of external parasites, or a combination of all of them. The levels were still significantly elevated compared to the captive-raised animals.

T3 and T4 Thyroid hormone levels for wild-caught animals were low but there was a gradual increase in their levels during the experiment. It is believed that the sensitivity of the test available for T3 and T4 were not sufficient to measure these hormones with the accuracy needed for our study. Reverse T3 had a downward trend for the wild-caught animals. Reverse T3 is an inactive breakdown product of T4, and is measured at MSU by an in-house method that is more sensitive than the one used for T3 and T4. The increase in T4 levels and the decrease in rT3, the inactive form of thyroid hormone, indicate that more T4 is being converted to T3, the active form of thyroid hormone. The total effect is an increase in metabolic activity. The enclosures allowed wild-caught animals to move around but they could not travel any distance and food was provided without the necessity of hunting. It was concluded that the increase in metabolic activity was caused by the increase of nutrients in the diet. It was concluded that that the anemia was caused by the presence of leeches, blood parasites and nutrient deprivation while the poor body condition was primarily caused by nutrient deprivation.

References

1.  Barnett JD, Cardeilhac PT, Barr B, Wolff W, Bass OL, DM Fleming. 1998. Utilization of thyroid hormone levels to determine starvation in alligators from the Everglades National Park. IAAAM Proceedings. Pp. 52-56.

2.  Glassman AB, Holbrook TW, CE Bennett. 1979. Correlation of leech infestation and eosinophilia in alligators. Journal of Parasitology 65:(2):323-324.

3.  Glassman AB, Bennett CE, TC Hazen. 1981. Peripheral blood components in Alligator mississippiensis. Trans. American Microscopical Society 100:(2):210-215.

4.  Khan RA, Forrester TM, Goodwin TM, CA Ross. 1980. A haemogregarine from the American alligator (Alligator mississippiensis). Journal of Parasitology 66:(2): 324-328.

5.  Barnett JD, Cardeilhac PT, McGuire PM, Fleming DM, Bass OL, Barr B, W Wolff. 1997. Chronic inflammation in American alligators (Alligator mississippiensis) in the Everglades. IAAAM Proceedings. Pp.49-52.