Abstract

HAS is caused by infections with opportunistic bacteria of low virulence which are noninvasive to the alligator. The major effect of HAS on the hatchling is poor performance (runting, stunting or sometimes death). Infections usually occur when the hatchlings are stressed. Four (4) levels of Virginiamycin (0 , 28 , 56 , 84 mg/kg of feed) were tested. Twelve (12) pens of animals, dispersed throughout the nursery, were randomly assigned a treatment level. Lengths and weights of all animals were taken at the beginning of the trial and after 51 days of treatment. Growth rates (daily increases in length) and body condition 3 Weight/Length) x 10001 were determined for each animal. The numbers of deaths, stunted animals and runts were determined. Runts were defined as individuals with growth rates below the confidence limit f o r the defined normal growth rate; while stunted animals were defined as runts with a body condition below the confidence limit for condition. The lower confidence limits were defined at approximately 80% of the mean growth rate of a rapidly growing group and 96% of the group mean condition. Virginiamycin, at levels of 28, 56 and 84 mg per kg of feed, was found to reduce the number of stunted animals and runts. Best results were obtained at the level of 84 mg per kg of feed.

Introduction

The most serious disease problem for alligator production is HAS (1,2,3,4). This disease is a complex of bacterial infections caused by opportunistic organisms which are of low virulence and usually noninvasive to the alligator. Infections by these organisms follow stress to the animal induced by a management problem (nutrition, handling, heat, cold, crowding) (1,2,5). The major effect of HAS on the hatchling is poor performance (runting, stunting or death) Previous studies have shown that HAS is best controlled by proper management and the addition of antibiotic to the feed before the infections occur. Proper management includes maintaining the hatchlings between 86 and 92 degrees Fahrenheit, carefully avoiding stress and feeding a good moist ration containing at least 20% protein by weight (1). Oxytetracycline has been used at 300 PPm to control the gram negative HAS organisms (2). An agent and regimen to control gram positive organisms has not been developed. In the present study, we present evidence that Virginiamycin, when added to the feed at 84 ppm, is effective in limiting HAS.

Performance Criteria

Lengths were measured to the nearest 1/4 inch. Weights were measured to the nearest gram. Body condition (condition) was the cube root of weight, divided by length, multiplied by 1000 [(cube root (weight/length)) x 1000] (1). Growth rate, over a period of time, is the mean daily increase in length x 1000. The standard deviation for growth rate has been found to have a mean value of about 10% of the growth rate for well managed, rapidly growing hatchlings. A defined confidence interval for normal growth rate was +/- 20% of the mean growth rate (about 2 normal standard deviations above and below the mean value) of a healthy, rapidly growing group. The standard deviation for normal body condition has been found to be 2% of the mean value for well managed, rapidly growing hatchlings. A defined confidence interval for normal condition is +/- 4% (approximately 2 standard deviations).

A runt is defined as an animal with normal condition but with a growth rate below the confidence interval for normal growth rate (less than 80% of the mean value). A stunted animal is a runt with body condition below the normal confidence interval for condition (less than 4% of the mean value for condition) of the group mean value for condition.

Experimental Period

The experiment began approximately at hatch and lasted for 51 days.

Drug

Virginiamycin premix containing 2.2% active principle and manufactured by the Smith Kline Beckman Company was used in this study.

Groups

Four groups of animals were given feed containing the following concentrations of Virginiamycin (ppm): 0; 28; 56; 84. An antibiotic standard group was included and given feed containing 300 ppm Oxytetracycline (OTC) and 28 ppm Virginiamycin. This antibiotic combination is the most effective treatment that has been tested to control HAS. Each group contained 20 animals and each group was replicated 3 times. Thus, 60 hatchlings were used to test each level of antibiotic.

Group Performance

The mean growth rate for all 300 animals tested was 94 while the growth rate of the standard antibiotic group was 99. The 1ower confidence limit of normal growth was determined and animals with a growth rate less than 80 were considered runts. The mean body condition for all groups was 383. Runts with body condition less than 370 were considered to be stunted. There were 26 runts (9%) , 4 stunted animals ( 1%) with a total of 30 runted/stunted animals (10%) among the 300 tested (Table 1). No deaths occurred.

Runted

Eight (8 of the control animals (13%) were runts. Seventeen (17) of all animals treated with Virginiamycin (9%) were runts with best results for the hatchlings receiving 28 ppm where 4 animals (7%) were runts. The antibiotic standard group had only 1 (2%) runt.

Stunted

The control group had 1 (2%) stunted animal, while in all animals treated with Virginiamycin there were 3 (2%) stunted animals. Hatchlings treated with 84 ppm Virginiamycin and the antibiotic standard had no stunted animals.

Runted/Stunted Hatchlings

Twenty (20) hatchlings or 11% of the animals treated with Virginiamycin were runted/stunted animals while 9 of the 60 control animals (15%) were runted/stunted. Best results were obtained with animals treated at a level of 84 ppm Virginiamycin where 5 of 60 hatchlings (8%) were runted/stunted. One (1) animal of the 60 antibiotic control hatchlings (2%) was runted/stunted.

Table 1. The Effect of Virginiamycin on the Performance of Hatchling Alligators

Totals

 Test Period = 51 days (Sep 18 to Nov 10 1986)

 Runts = Growth Rate < 80 (Length/Day x 1000)

 Stunted = Condition < 370 [cube root (Weight/Length) x 1000]

 Runts in poor condition

 Assumed to be caused by HAS

 OTC = Oxytetracycline (Terramycin D- 50 premix)

Discussion

With better management, the incidence of HAS is reduced among farm-reared hatchling alligators. However, even the best farms have runts, stunted animals and deaths. Our laboratory has worked with 8 farms in Florida each producing approximately 1000 or more commercial animals annually. It appears that poorly performing animals (runted/stunted and deaths) should not exceed 15% of the hatchlings. Since HAS has been identified as the major cause of poor performance, the control of HAS is essential for increases in production efficiency.

Since gram negative organisms have been identified as the major component of HAS, the search for an efficient and economical agent with low toxicity was first directed toward controlling the gram negative invaders. Oxytetracycline (OTC) was chosen because of its long history of efficient use in domestic animals and fish. It proved to be effective in the alligator, with an optimum dose of 300 PPM (3) - Since some of the HAS organisms are gram positive, the search for an agent to control this group was initiated. Experience with OTC showed that an agent which was not used in the treatment of humans would have better prospects of FDA approval. Virginiamycin was chosen as an agent which might accomplish our goals of controlling gram positive organisms which contribute to HAS.

Results of the present study indicate that Virginiamycin at 84 ppm will indeed reduce the number of runted/stunted animals and this effect is enhanced when combined with OTC. This would be expected since both gram positive and gram negative organisms are controlled.

Acknowledgements

Technical assistance was provided by Florence Shrager. Dr . S.F. Sundloff , quality assurance; Dr. E.E. Viera, USDA IR-4 and Dr . A . Louis Shor, Smith Kl ine Beckman Company were project officers. The research was sponsored by Smith Kline Beckman Company and USDA IR-4.

References

1.  Cardeilhac, P.T. Nutr. Conf., Alligator Farming in Florida Proc. Florida Daytona Beach, FL, PP172-180 (1987).

2.  Lane, T., W. M. Boyce, M . K . Reinhard, R . E . Larsen, P . W . Poulos , M. M. King , C. Buergelt and P.T. Cardeilhac Disease problems in farm-raised hatchling alligators on Florida alligator farms. Proc. Int. Assoc. Aquatic An. Med. 1(1):9 (1984).

3.  Cardeilhac, P.T. , B. R. Collins , F. Ruisi , S. Sundloff , R. Larsen and T. Lane Preliminary studies on the use of oxytetracycline to control hatchling alligator syndrome (HAS) . Proc . Int . Assoc . Aquatic An. Med 1(3) 21 ( 1986).

4.  Cardeilhac, P. T Management Problems of hatchling alligators. Proc . Am . Assoc . Zoo Veterinarians Chicago, IL p120 (1986).

5.  Smith , J . and P . T . Cardeilhac Pen design and stocking densities for hatchlings , growout and reproduction. Proc. First Ann. Alligator Prod. Conf. Gainesville, FL p10 (1981).