Abstract

The effect of total food consumption and individual nutrients on reproductive performance in breeding colonies of American Alligators was studied. Twenty two breeding pens on one Florida farms were used in the study. Each pens contained from 23 to 230 animals with an average of 108. The diets were custom made and consisted of blends of meats (beef, nutria, horse, chicken, fish, etc) meat meals (fish, blood, poultry, meat & bone, etc.) vitamin-mineral mix and antibiotics. The reproductive parameters studied were nest rate, clutch size, egg yield, percent eggs that band, embryo survival, viable hatchling yield. Treatments consisted of varying the quantity of the following nutrients: protein; total fat; highly unsaturated fat; vitamins; antibiotics. A matrix of the correlations of concentrations of the different nutrients was made to identify their associations. Correlation of reproductive values (response variable) with quantities of a nutrient consumed (explanatory variable) was also made. It was found that nest rate was most closely associated with protein consumption (r = 0.4, r² = 0.16) and highly unsaturated fat (r = 0.36, r² = 0.13) but was not strongly correlated with total fat, vitamins or antibiotic intake (r² < 0.1). Clutch size was strongly correlated with total fat (r = 0.57, r² = 0.33) and protein consumption (r = 0.50, r² = 0.25) but not strongly correlated with highly unsaturated fat, vitamin or antibiotic intake (r² >0.1). Percent of the eggs that develop a grossly detectable chorioallantoic band ("fertile egg") is strongly correlated with antibiotic (r = 0.64, r² = 0.41) therapy and with highly unsaturated fat consumption (r = 0.40, r² = 0.16) but had a negative correlation (r = - 0.58, r² = 0.34) with total fat and protein (r = 0.56, r² = 0.31) intake. The effect of nutrients on embryo survival was confounded by variation in age of the breeders but an estimated ranking of the nutrients as to beneficial effects is as follows: l) total fat; 2) vitamins; 3) antibiotics; 4) highly unsaturated fat; 5) protein.

Introduction

Human populations, since their origin, have harvested wildlife and this utilization permitted their emergence and evolution. Although we thrived on the utilization of wildlife, our reproductive success and technology finally overburdened wildlife populations. This was manifested by extinctions and severe declines in wildlife numbers. A change in strategy was required. We had to supplement the uncontrolled wild harvest with farming and implement sustained yield utilization of the wildlife to prevent its extinction. Most conservationists no longer oppose sustained yield utilization because of its importance in the conservation of wildlife and habitat. Sustained Yield Utilization was adopted into the World Conservation Strategy in 1980 (1).

The decline in world population of crocodilians has prompted an intensive study of reproductive parameters of these aquatic animals. Loss of habitat is still a major cause of decline and consequently crocodilians are frequently being managed by more intensive culture in smaller areas. Alligator ranching and farming in the U. S. is an example of the intensive culture of crocodilians. Breeding areas (pens) are essentially alligator habitat where the wetland has been increased, ponds deepened, stocking density increased and the alligator breeders fed. Bird populations and other wildlife that utilize alligator habitat have also been observed to dramatically increase in the breeding areas.

However, breeding areas are commercial ventures where the owner intends to harvest alligator eggs. Almost all of the eggs produced would fail to result in viable hatchlings if not harvested because of flooding, predation or cannibalism. The managed harvest of alligator eggs has little impact on wildlife populations, especially since the alligator population in breeding areas is maintained at high densities. Our laboratory has investigated infertility in the breeding areas in order to increase the reproductive rate and make them economically more attractive to the farmer.

Methods

The present study was made over 5 years on the 52 acre breeding area (divided into 8 pens) of a south Florida alligator farm. Individual pens in the breeding area ranged in size from 1.5 to 20 acres and each pen continued from 23 to 230 breeders (average number = 108). The pens had stocking densities ranging from 11 to 17 breeders per acre with a mean value of 13.5. Sex ratios (females/males) for the individual pens ranged from 2 to 5 with an average value of 2.8. Annual reproductive performance for each pen was considered an individual observation and the reproductive values were the mean values for the pen in one of the study years. Each pen had females of uniform age but the data were sorted so that only pens with breeders ranging in age from 7 to 20 years during the study period were used (22 observations). Females from 7 to 20 years are considered to be in breeding prime. Mean age for females in all pens studied was 10 years.

The breeders were fed home-made diets composed of tankage meats supplemented with protein, free amino acids, fat, vitamins, minerals and antibiotics. The meats were horse, beef, pork, chicken, fish (catfish and tilapia). The supplement contained meat meals, free amino acids, antibiotics and a vitamin-mineral pre-mix. The meat meals consisted primarily of meat and bone meal, fish meal, blood meal and feather meal. Protein meals and free amino acids were mixed to approximate an amino acid profile consistent with alligator egg protein. Consumption was also based on published amino acid absorption and utilization data (2). Highly unsaturated fat ((C18:1n9, C18:2n6, C18:3n3, C20:1n9, C20:4n6, C20:5n3, C22:1n11, C22:6n3) was obtained by adding liver, fish oil and fish tankage to the diet. The estimated concentration of protein and total fat by calculation was checked by random proximate analysis of certain feedstuffs.

One hundred grams of the vitamins and trace mineral mix contained the following: vitamin A. 220,000 IU; vitamin D3, 55,000 IU; Vitamin C, 300 mg; vitamin E, 14,500 IU; Menadione, 300 mg; Riboflavin, 132 mg; Pantothenic Acid 220 mg; Niacin, 700 mg; Folic Acid, 18 mg; Vitamin B12, 0.22 mg; Biotin 3.5 mg; Pyridoxine 88 mg; Thiamine 44 mg; Copper 18 mg; Manganese 1,320 mg; Iron 176 mg; Selenium 6 mg; Iodine 18 mg. Each gram of the antibiotic mixture ("gator Cillin") contains 200 mg of virginiamycin and 800 mg of oxytetracycline.

The reproductive parameters studied were nest rate, clutch size, egg yield, percent eggs that band (grossly detectable chorioallantois), embryo survival, and viable hatchling yield. Treatments consisted of varying the quantity of the following nutrients: total feed; protein; total fat; highly unsaturated fat; vitamins; antibiotics. The correlation of varying nutrient consumption as an explanatory variable with reproductive parameters as the response variable was determined (r and r²).

Percent Correlation of Nutrient Concentrations in Breeder Diets

(Estimated by r2 X 100)

Annual feeding rates per breeder were varied from 40 lbs to 171 lbs (105 lbs average) per year given in approximately 30 feedings from March to December each year. Feeding rates at this level are considered to be below those known to produce obesity.

Nutrient consumption was varied as follows: 1) protein, from 7 to 27 lbs (average 17); 2) total fat, from 1 to 14 lbs (average 5); highly unsaturated fat from 0.4 to 3.9 lbs (average 2.3). Vitamin additions to the diet varied from O to 510 grams (average 243) and antibiotic additions ranged from 0 to 9 grams (average 3.7). Eggs from the breeding area were collected during June, July and August and incubated under standard conditions (3). Hatchling vigor was high for the farm with greater than 95% becoming commercial animals (36 inches in length).

Results

Reproductive Rate

Annual reproductive rate for the colony ranged from 2 to 12 hatchlings per breeder (average 7.1) for all pens over the 5 year study period. Hatchling yields for the females ranged from 3.5 to 17.6 (10.4 average). Reproductive rate for the colony is influenced by the sex ratio of the colony (females/males). Previous studies have shown that a sex ratio of 2 to 5 will produce the highest % of eggs that band. The average value for sex ratio in the present study was 2.8.

Nest Rate

Nest rates (% of females that nest} ranged from 25 to 81. The strongest association (r = 0.42, r² = 0.18) was seen with protein consumption, followed by total feed consumption (r = 0.40, r² = 0.16) and highly unsaturated fat consumption (r = 0.36, r² = 0.13). Total fat consumption at the feeding rates used was not associated (r = 0.13, r² = 0.02) with nest rate but vitamin and antibiotic intake were weakly associated (r = 0.27, r² = 0.07; and r = 0.23, r² = 0.05 respectively).

Clutch Size

Total fat in the diet was strongly correlated (r = 0.57, r² = 0.33) with clutch size followed by protein (r = 0.50, r² = 0.25) and total feed (r = 0.49, r² = 0.24). Highly unsaturated fat not associated with clutch size (r = 0.01, r² = 0.00) but vitamin and antibiotic therapy had slight negative associations (r = - 0.19, r² = 0.04 and r = - 0.23, r² = 0.05 respectively).

Percent Banding

Percent of the eggs that develop a grossly detectable Chorioallantois (fertile eggs) is strongly correlated with antibiotic and vitamin therapy (r = 0.64, r² = 0.41 and r = 0.58, r² = 0.34 respectively) followed by highly unsaturated fat (r = 0.40, r² = 0.16). Total fat consumption has a strong negative correlation (r = 0.58, r² = 0.34) followed by total feed and protein intake ((r = 0.56, r² = 0.31).

Embryo Survival

The effect of nutrients on embryo survival was confounded by the stronger effect of age on this parameter. Beneficial effects of nutrients estimated in numerical order were as follows: 1) total fat; 2) vitamins; 3) antibiotics; 4) highly unsaturated fat; 5) protein; 6) total feed.

Discussion

It is difficult to evaluate the effects of consumption of basic nutrients or vitamin and antibiotic therapy on reproductive performance of alligators kept in an almost wild habitat. Stocking densities were about 100 times those found in good wild habitat; thus, it was assumed that the breeders did not receive a significant quantity of nutrients from pray or other sources in the breeding area. Although individual pens had females of almost uniform age the entire study had females that ranged in age from 7 to 20 years. The affect of age on embryo survival so confounded the results that it was possible to only estimate any beneficial effects of nutrients on this reproductive parameter. Age affects other reproductive parameters as does stocking density and sex ratios (3). The effects of stocking densities and sex ratios were considered to be negligible and/or canceled out. The experiments were performed on one farm therefore other effects such as differences in mean daily temperature, type of habitat or other factors should have been similar. The use of pens containing a average of 108 breeders probably reduced the effects of individual variation. The use of mixed feedstuffs permitted the variation of one nutrient (with the exception of vitamins and antibiotics and to a lesser extent protein and fat) without it being totally dependent on concentration of another nutrient. This strategy allowed the effects of one nutrient to be tested without being completely associated with the concentration of another nutrient. Antibiotics and vitamins were tested separately in an attempt to separate their effects (4). The levels of feeding were low enough (40 to 170 lbs per year) that the effects of obesity were considered negligible.

Associations of nutrient intake, at the limiting levels tested, with responses in reproductive values was estimated by correlation coefficients and their square (r and r²) which is considered the most direct manner available. From the results it seems clear that nest rate is enhanced by protein and highly unsaturated fat consumption when the total quantity of nutrients ingested is low. Clutch size is most strongly affected by total fat consumption followed by protein. Percent of the eggs that grossly show a chorioallantoic band is strongly increased by antibiotic and vitamin therapy followed by consumption of highly unsaturated fat. Separate experiments show that the greatest effect is due to antibiotic therapy (4).

Although these experiments have made many assumptions some of the results seem clear. The conclusions when put into practice have caused dramatic increases in hatchling production on the two breeding colonies where it has been possible to implement most of them. Hatchling production has increased on the study farm from about 1, 115 before the study to 5,070 at the end of the study. Reproductive rate increased from 2.1 to 7.8 for the farm. A second farm, following the procedures learned in the present study, started full production in the last year of the study and produced 4711 hatchlings with a reproductive rate of 6.3. It is hoped that the reproductive success of these farms continues and will encourage the use of breeding areas as a part of farming or ranching operations to augment production and income. We also hope that this information will ultimately aid in conservation of all crocodilians.

References

1.  Messel, H. Crocodile Specialist Group Newsletter. Vol 9, No 3. p.2, 1990.

2.  Coulson R. A. and Hernandez T. Alligator Metabolism Pergamon Press pp 59-137, 1983.

3.  Cardeilhac, P. T. Husbandry and Preventative Medicine Practices that Increase Reproductive Efficiency of Breeding Colonies of Alligators. Final Reports for the 1988-89 Aquaculture Market Development Aid Program. Vol II. pp90 115. Florida Dept of Ag and Consumer Serv. Mayo Bldg. Tallahassee Fl 32399-0800.

4.  Cardeilhac, P. T and Ted Joanen. Reproduction and Development of the American Alligator. Proceedings Crocodilian Congress Production and Marketing, Strategies for the 1990's. Tampa Florida 1989.