Abstract

Diseases of bacterial origin are commonly encountered in cranes.² Administration of antimicrobial medications is often challenging due to inconsistent acceptance of medicated treats (e.g., fish, rodents), multiple bird enclosures, and stress of daily handling. Administering antimicrobial drugs within the drinking water would provide a low-stress means of treating bacterial infections in cranes.

Enrofloxacin (Baytril®, 3.23% Concentrate Antimicrobial Solution, Bayer Corporation, Shawnee Mission, KS, USA) is currently approved for use in non-laying chickens and turkeys for the control of E. coli and Pasteurella multocida infections. Mean plasma concentrations of enrofloxacin in both poultry species were maintained above 0.2 µg/ml by adding the medication to drinking water at concentrations of 25 and 50 ppm. The MIC₉₀ values for E. coli and P. multocida isolates from natural infections in poultry were 0.06 and 0.03 µg/ml, respectively.¹

This three-phase study was designed to determine if therapeutic plasma concentrations of enrofloxacin and its metabolites could be achieved and maintained in sandhill cranes (Grus canadensis) after administration in drinking water at a concentration of 50 ppm. Eight adult sandhill cranes housed at the International Crane Foundation were utilized for this study. Two male/female pairs were housed in shared pens, and two male/female pairs were housed in divided pens. Food (Mazuri Crane Maintenance Diet, St. Louis, MO, USA) and fresh water were provided ad libitum in buckets within the enclosure. In phase I (14 days’ duration), daily food and water consumption were measured in order to establish controls for the treatment period. The cranes were handled and weighed on days 0, 2, 6, 10, and 14 in order to mimic the handling during the treatment period. Phase II (7 days’ duration) was a “washout” period during which only food and water consumption were monitored. In phase III (14 days’ duration), enrofloxacin concentrate was added to the drinking water at a concentration of 50 ppm (9.4 ml enrofloxacin solution/6.0 L water). Food and water consumption were measured daily during the treatment period. The cranes were restrained on days 0, 2, 6, 10, and 14 for weighing and venipuncture for plasma analysis of enrofloxacin/ciprofloxacin levels. Water samples from two enclosures were collected on days 2 and 10 (fresh medicated water) and on days 3 and 11 (used medicated water) in order to evaluate enrofloxacin/ciprofloxacin concentrations.

Twenty-four-hour food and water measurements indicated that manual restraint had a negative effect on food and water consumption immediately following handling in most birds, but weights of all study birds remained stable between phases I and III. The addition of enrofloxacin to the drinking water did not have a negative effect on food and water intake. In fact, consumption of food and water increased in many birds during the treatment period, but only one bird approached significant weight gain during phase III.

Plasma and water samples were analyzed by HPLC analysis for enrofloxacin and ciprofloxacin concentrations. Water analysis revealed adequate drug levels in both fresh and used samples. Mean enrofloxacin and ciprofloxacin plasma values and corresponding standard deviations for all study birds are listed in Table 1. Birds in divided pens had slightly higher mean enrofloxacin plasma concentrations than individuals in shared pens. Ciprofloxacin plasma concentrations were not different between paired and unpaired birds.

Table 1. Enrofloxacin and ciprofloxacin plasma concentrations (mean±SD) for sandhill cranes (n=8)

The plasma concentrations of both drugs were extremely low compared to in vitro MIC values for common bacterial pathogens.³ It is uncertain why plasma concentrations are low in light of adequate enrofloxacin concentrations in drinking water. Since all plasma samples were collected in the early morning, it is possible that the concentrations measured were more likely associated with “trough” rather than “peak” concentrations. Further studies are needed to evaluate plasma enrofloxacin concentrations sampled at multiple time points throughout a 24-hour period in order to determine whether therapeutic concentrations can be achieved in sandhill cranes.

Acknowledgments

We would like to thank the Crane Conservation Department staff at the International Crane Foundation for their support and assistance during this project, especially Carolyn Pauly, Nat Warning and Tori Kaldenberg. We would also like to thank Dr. Keven Flammer and Dr. Mark Papich at North Carolina State University for comments on study design and sample analysis, respectively.

Literature Cited

1.  Bayer Corporation. Baytril® 3.23% Concentrate Antimicrobial Solution. Package insert. 2002.

2.  Olsen, G.H., J.W. Carpenter, and J.A. Langenberg. 1996. Medicine and surgery. In: Ellis, D.H., G.F. Gee, C.M. Mirande (eds.). Cranes: Their Biology, Husbandry, and Conservation. National Biological Service, Washington, D.C., Pp. 155–156.

3.  Scheer, M. 1987. Studies on the antibacterial activity of Baytril. Vet. Med. Rev. 2: 90–99.