Background: Florfenicol (Ff) is a synthetic antibiotic with a broad antibacterial spectrum and high therapeutic effectiveness that was specifically developed for veterinary use as well as, doxcycline is an antibiotic synthetically derived from oxytetracycline.
Methods: In the present study, the in-vitro efficacy of Ff and doxcycline against Salmonella entertidis and Escherichia coli (Serotype O78) pathogens was determined using disc diffusion technique and Minimum inhibitory concentrations (MICs). In the other hand serum and tissue residual levels of Ff and doxcycline after intramuscular (i.m.) administration of 30 mg/kg and 250 mg/kg orally respectively to 5 weeks old chicken were determined using microbiological assay method with Bacillus subtilis ATCC 6633 as a reference organism.
Results: The results showed that both microorganisms were highly susceptible to Ff with lower MIC value than those of doxcycline. The peak concentration of florfenicol in serum was 5.34

In the present study the anticryptosporidial efficacy in chickens of two commercially available antibiotics, norfloxacin and spiramycin, in the drinking water alone or in combinations with one commercially available anticoccidial (clopidol) treatment in ration were used. At day 6 of chicken life, 210, male, white Hy-Line chicks were divided into 7 groups (1-7), 30 in each group. Chickens of first group (G1) served as negative control uninfected-untreated group (UUC). Birds of the second group (G2) were inoculated orally with inoculum containing 5X105 Cryptosporidia baileyi (C. baileyi) oocysts/chick and served as infected-untreated positive control group (IUC). All birds of groups 3 to 7 infected with 5X105 C. baileyi oocysts/ chick and treated with 12mg/kg BW norfloxacin (G3), 1gm/10kg BW spiramycin (G4) from 1st to 5th days post-infection (DPI) and 0.5 gm/kg ration (125ppm) Clopidol (G5) from one day old chick up to one week PI. Last two groups were infected similarly and treated with both of norfloxacin+clopidol (G6) or spiramycin+clopidol (G7) with the same previous dose and course of each treatment. The efficacy of the tested medicaments were evaluated by daily count of cryptosporidia oocysts in the feces of chicks, mortality percentage, body weight gain, the degree of histopathological changes of Bursa of Fabricius and lesions score. The results showed that the mortality rate reached 10% in (spiramycin and/or clopidol) treated groups, 6.7% in norfloxacin treated group and 3.3% in norfloxacin+ clopidol treated group while it reached 13.3% in infected-untreated control group. High bursal lesion score was recorded in infected-untreated group followed by infected treated chicken groups regardless the type of medicated drugs. Total oocyst per gram feces of experimentally infected chicks with C. baileyi was reduced significantly in all infected treated groups regardless the type of used medicaments when compared with other infected-untreated control chicken group. The recommended dose of norfloxacin and norfloxacin + clopidol decreased the oocyst output of birds by 62% and 63%, respectively. While, other groups showed lower efficiency percentages 43% (spiramycin + clopidol), 40 % (spiramycin) and 35 % (clopidol). Also, non significant differences were observed in body weight gain on day 28 of chicken life between uninfected control and infected groups. Finally, none of these drugs alone can be entirely suggested for the chemotherapy of avian cryptosporidiosis. While, in addition to application of good sanitary measures and disinfection, the present study may conclude that the administration of both norfloxacin in drinking water at 1st to 5th DPI and clopidol in ration one week before and after infection may be helpful in prevention and treatment of cryptosporidiosis in chickens.