Introduction

World crocodilian populations are in decline with 12 of the 22 recognized species classified as endangered. Some species such as the Siamese Crocodile, Chinese Alligator and Cuban Crocodile may survive primarily in captivity. Genetic purity of these captive species has become questionable because of interbreeding that may occur when different species are kept together at high densities. Strategies for enhanced efficiency of captive breeding have been investigated in our laboratory because of the poor status of crocodilian populations. We use the american alligator as a model species. The work is focusing on the following projects: 1. identifying and treating infertility; 2. reducing the time period required to reach reproductive prime; 3. increasing the number of hatchlings that reach maturity 4. Egg fertilization by artificial insemination; 5. Control of the portion of progeny that are females; 6. Evaluating genetic status (integrity).

Methods

Normal reproductive statistics were determined from several alligator farms in Florida, and wild animals from Florida and Louisiana (the Louisiana Department of Wildlife and Fisheries, T.J.). Fifty observations were made on breeding pens at Florida farms over a 4 year period (1 observation per pen per year but up to 4 observations on a single pen). Each pen contained from 15 to 526 animals resulting in a total of 5052 animal observations. Normal hatch rates and normal hatchling growth performance values for this study were determined from data obtained from 606 eggs from 18 clutches collected in Cameron and Vermillion Parish of Southeast Louisiana on June 26 of years 1988 and 1989. Egg quality was determined by measuring clutch size, egg size, egg shape, hatch rate, incubation period, hatchling length (at hatch) , degree of hydration and % of the egg weight at lay represented by the hatchling. Growth rate and condition of hatchlings were determined approximately 95 days after hatching (December 15 in 1988 and 1989). Calculations used to determine growth performance of the hatchlings have been described (1). The hatchlings were fed supplemented horse meat diets containing 21% to 25% protein, 1.7% to 5% fat and less than 1% carbohydrates. The diets contained approximately 125 (+/- 15) Cal/100 g. Some of the diets were supplemented with 300 ppm, oxytetracycline and/or 80 ppm virginiamycin. In one study feed consumption was measured in diets where the energy and protein content were fixed at different levels and feed/gain, protein/protein gain, energy/g protein gain and PER were determined.

The incidence of runting, stunting and death (RSD) was determined in the hatchlings. Animals suspected of having bacterial infections (Hatchling Alligator Syndrome or HAS) were examined for pathogen isolation-identification and antibiotic sensitivity (3). The percentage of viable hatchlings (projected to reach maturity) was determined from growth performance data.

The effect of age, stocking densities, and feeding rates on reproductive performance was determined from those breeding pens where: 1. age was uniform and known; 2. quantities of feed were measured and feed management practiced; 3. pen characteristics, dimensions and stocking densities known; 4. females/male known.

Results

Infertility

Alligators less than 4-years-old did not lay in our study and have not been reported to lay by others. The small percentage of 4-year-old females that did lay had been cultured for 3 years in heated houses and fed supplemented diets. Eggs from 4-year-old females were usually infertile and the animals had to be approximately 7 years old before mean hatchling yield was greater than 5/female. Females greater than 20-years-old were erratic in performance and found to be past reproductive prime for captive breeding under the conditions of Florida farms. Farm-reared females were in reproductive prime from 7 to 20 years of age. Stocking densities (breeders/acre) for the 50 pens ranged from 10 to 96 with a mean value of 18. Mean annual feed consumption per breeder was 144 but ranged from 72 to 274. Sex ratios (females/males) ranged from 2 to 5 with a mean value of 2.8. Farm-reared females known to be in reproductive prime had reproductive rates ranging from 0.7 to 17.6 with a mean value of 8.

Breeder management and treatment programs were started in 1986 on the primary study farm (HT) for breeding pen management. Farm HT has approximately 500 females and 8 breeding pens. Stocking densities (breeders/acre) of the breeding pens ranged from 10 to 20. The reproductive rate on farm HT increased from a mean value of 4.7 in 1986 to 11.4 in 1989. The percent of hatchlings that were viable increased from 56% in 1986 to 98% in 1989. Management changes were: 1. increasing the percentage of females in reproductive prime; 2. increasing protein concentration of the breeder and hatchling feed; 3. the addition of antibiotics to both breeder and hatchling feed; 4. changes in hatchling management.

The mean reproductive rate of captive females for the state of Florida was 2.7 in 1986 and 2.5 in 1989 indicating that fertility remained constant at about 13% of normal (20 = normal).

Major causes of infertility for Florida farms were identified as: 1. excessive stress primarily caused by high stocking densities and poor feed management; 2. high percentages of females out of reproductive prime; 3. breeding pens that do not permit female breeders some degree of seclusion.

Reproductive Rate and Period of Reproductive Prime

Normal mean reproductive rate is 20 (1,2) and the period of reproductive prime was found to be about 10 years. Reproduction by a single normal female for the 10 years of prime would be 200 F1 progeny with about 50% female. The 100 normal F1 females should produce 2,000 F2 during their reproductive prime. At a reproductive rate of 10 the number of F1 progeny would be 100 and the F2 would be 5,000. Thus doubling the reproductive rate quadruples (4X) F2 progeny production.

Production of All Female Progeny

Techniques have been reported that allow the production of all female progeny (5). If all F1 progeny were females and reproductive rate were 20 there would be 4,000 F2 progeny (instead of 2,000) from the 200 F1 progeny produced by a single normal female. Thus doubling the number of F1 female progeny doubles (2X) F2 progeny production.

Age at Reproductive Prime

Age at reproductive prime was determined to be 7 years on farm HT although some animals will lay during the fourth year. Age at sexual maturity for Louisiana alligators held in semi-natural outside pens was reported to be 9 years (4). Thus, the use of controlled culture conditions for the first 3 years will reduce the age required to reach prime by at least 2 years. Reducing the time required to reach prime eventually has the greatest effect of any of our strategies on increasing reproduction by a population of alligators. A reduction of 1 year will have an effect, if sufficient time is allowed, greater than producing all females or doubling reproductive rate.

Discussion

Our studies describe some of the usual problems found with attempts at captive breeding of crocodilians. In addition to preventative medicine procedures most of the problems causing infertility can be controlled by the relatively simple husbandry practices described, such as, keeping only animals at reproductive prime in the breeding pens, proper stocking densities, well designed breeding pens and feed management.

The determination of causes of infertility in a breeding colony is facilitated by the availability of normal reproductive statistics which are now known for the alligator (1,2,3,4,5). Treatment of infertility can result in a significant increase in the reproductive rate. For example, the reproductive rate more than doubled on farm HT over a 3 year period while mean reproductive rates for all Florida Farms remained constant. Reproductive rate has the most importance to the alligator producer since he is primarily interested in increasing the production of F1 progeny by mature females and this is most affected by reproductive rate. Treating infertility and hatchling management are the best methods for the producer to increase reproductive rate.

Reducing the age at prime and producing high proportions of females progeny may be most important in captive breeding for restocking projects. The state of Louisiana is now releasing animals that have been cultured in heated houses for about 2 years. The cultured animals should reach reproductive prime at least 2 years ahead of animals raised in the wild. There are no experiments reported where release was made with only cultured females.

These studies show that the normal reproductive rate of the alligator is high enough to allow a few animals to produce several thousand F2 progeny in only a few years on a relatively small site. Farm HT used 500 females to produced 5,500 hatchlings on approximately 42 acres in 1989. Modification of the procedures used in this study would be necessary to meet species differences but at this reproductive rate a production area of less than 500 acres would allow all of the 12 endangered species of crocodilians to be cultured with the production of several thousand progeny annually. Intensive culture of these hatchlings for 2 years and the release of mostly females should cause the rapid restoration of these animals in a suitable protected habitat. This technique would also help in areas where alligators are wild harvested.

Acknowledgement

We thank Ted Joanen of Rockefeller Wildlife Refuge Grand Chenier, Louisiana 70643, for his generous support and supplying the fertile eggs necessary as standards to verify our techniques.

References

1.  Cardeilhac, P.T. Husbandry and Preventive medicine Practices that Increase Reproductive Efficiency of Breeding Colonies of Alligators. Final Reports for the 1987 - 1988 Aquaculture Aid Program. Florida Department of Agriculture and Consumer Services. pp 90 - 115. 1989.

2.  Cardeilhac, P. T. and Schumacher J. Feed Management to Control Disease and Infertility in Crocodilians. Proceedings American Association of Zoo Veterinarians. 1989. pp 139 142.

3.  Cardeilhac, P. T. and Peters D.K. Estimation of an Effective oral Dose of Virginiamycin to Control Hatchling Alligator Syndrome (HAS). Proceedings IAAAM Conference 1987 1(4) 184 - 188.

4.  Joannen, T. and McNease, L. Alligator Farming Research in Louisiana. IN: Wildlife Management: Crocodiles and Alligators. Surrey Beatty & Sons Pty Ltd. pp 329 - 340.

5.  Ferguson, M. J. W. and Joanen T. Temperature-dependant Sex Determination in Alligator mississippiensis. J. Zoology 200 143-177. 1983.