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The production of NH + % -N following in vitro incubation of cattle urine was monitored for 24 h in the presence of ampicillin sodium salt (0, 32, 64, 128 mg\l), hydroquinone (0, 16n7, 33n4, 66n8 mg\l), wheat straw (0, 3n3, 6n6, 13n2 g\l) or spruce sawdust (0, 3n3, 6n6, 13n2 g\l) with (20 IU) or without urease. Each concentration of ampicillin, hydroquinone, wheat straw or spruce sawdust was tested in triplicate.The equipment consisted of Woulff flasks containing 300 ml of a buffered solution (0n02  ; pH 7n50) with 1 ml of cattle urine. The cattle urine was characterized by measuring the main nitrogen contents, which were 6n52 mg total-N\ml, 5n96 mg urea-N\ml and 0n026 mg ammonium-N\ml. The initial pH of urine was 7n84. Ammonium and nitrate concentrations, and pH were monitored at zerotime and after 3, 6 and 24 h of incubation with the cattle urine.The addition of urease to the flasks containing urine induced a significant increase in the production of ammonium-N, from 1n83 to 6n32 mg NH + % -N\flask after 24 h of incubation. In the presence of urease, an inhibitory effect was recorded in NH + % -N production with ampicillin and spruce sawdust. In contrast, hydroquinone inhibited urease activity and wheat straw adsorbed the NH + % -N produced, both causing a dose-dependent relationship. In the absence of urease, ampicillin, hydroquinone, wheat straw or spruce sawdust caused a doserelated decrease in NH + % -N production. However, the highest amounts of wheat straw (6n6 and 13n2 g\flask) exhibited a temporary increase in NH + % -N production during the first 6 h. This is probably due to a generation of extra NH + % -N as compared to the control flasks without straw. However, at 24 h, the situation paralleled the other materials.Although pH increased approximately from 7n50 to 7n65 during the hydrolysis of urea in the presence of urease, no gaseous ammonia was volatilized into a 0n1  HCl flask. Moreover, no increase in nitrate concentration was found during the incubation.The present results suggest that ampicillin, hydroquinone and spruce sawdust could be used in order to reduce NH + % -N production from cattle urine. The NH + % -N already produced could probably be absorbed on wheat straw.

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During the treatment of fish diseases, drugs which inhibit the nitrification process can cause acute ammonia toxicity. The same phenomenon can occur when fish are put into a tank without active cultures of nitrifying bacteria. The purpose of this study was to quantify the inhibitory effects of 15 pharmacological agents, which are often used as therapeutic agents in ichthyopathology, on ammonia removal and nitrate production in a simple closed aquatic system. The experiments were conducted in polyethylene bags containing activated biofilters and synthetic water solutions, held in a water bath. Ammonia was added to initiate the nitrification process, and graded concentrations of various pharmacological agents were added. The effects of the pharmacological agents on in vitro nitrification were assessed by monitoring ammonia and nitrate concentrations compared to controls with no added agents, for 24 hours. Graded concentrations of ampicillin (Albipen®), chloramine T, enrofloxacin (Baytril®), erythromycin, levamisole, methylene blue and polymyxin B induced dose-dependent inhibitions of ammonia removal and nitrate production. The corresponding linear regression curves showed high correlation coefficients and were highly significant (p < 0.05). The addition of chloramphenicol, copper (II) sulphate, kanamycin disulphate, malachite green, neomycin sulphate, potassium penicillin G, tetracycline and a mixture of trimethoprim and sulphadoxin (Duoprim™) had no significant effects on the nitrification process. A significant dose-related inhibition of nitrate production, but not of ammonia oxidation, was observed with enrofloxacin. The significant correlation (r = 0.940; p < 0.001) between the degrees of inhibition of ammonia oxidation and nitrate production for the various inhibitory pharmacological agents has also been calculated, with a view to validating this method. The data presented suggest that separate tank facilities for hospitalisation or quarantine are necessary when treating diseased fish with ampicillin, enrofloxacin, chloramine T, erythromycin, levamisole, methylene blue or polymyxin B, in order to avoid ammonia poisoning.