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Although no microbiological activity was found in blood plasma during treatment of broilers through the drinking water with spectinomycin or lincomycin-spectinomycin, these drugs proved highly effective in treating experimentally induced colibacillosis. This efficacy may be produced by a metabolite or a degradation product of spectinomycin that reaches the infection site in the respiratory tract and interferes with adherence of bacteria.

The Nurmi concept for diminishing salmonella infection of poultry by application of gastrointestinal microflora from adult birds into newly hatched chicks was tested in a field study in which 8 million broilers were involved. Half of the 284 flocks was treated in the hatchery by spray application of an undefined microflora propagated in SPF chicks. A significant reduction in salmonella-contaminated flocks, as well as in the number of infected broilers in these flocks was demonstrated. No undesirable side effects were detected. It was concluded that hygienic improvements in transportation and slaughtering of broilers are needed in order to maintain the reduced salmonella contamination rate.

The efficacy of spray application of intestinal microflora of the adult bird in protection of broilers against salmonella infections was studied in 3 experiments under laboratory and field conditions. In chicks treated soon after hatching (in the hatchers at approximately 30 per cent hatch or in the chick delivery boxes in the hatchery) with crop-caecum homogenate or a mixture of aerobically and strict anaerobically cultured intestinal flora, very good results were achieved. A very obvious protective effect against a high infection dose (3 X 10(6) c.f.u.S. infantis bacteria per chick) and complete protection against natural infection with different salmonella types was induced. A significant improvement of growth rate was observed in broilers treated by spray in the hatchery and reared for 7 weeks under field conditions in an environment heavily contaminated with different salmonella types.

Pharmacokinetic studies in broilers and layers of different sulphonamides indicate a good absorption and a long elimination half-life (of sulphaquinoxaline, sulphadimidine and to a lesser degree sulphadiazine) resulting in high plasma concentrations during drinking water medication in the recommended therapeutic doses. In contrast drinking water medication with high concentrations of trimethoprim (up to 1,320 mg/liter) resulted in a maximal mean plasma concentration of 1.2 micrograms/ml. Very good therapeutic effects were demonstrated in broilers experimentally infected with a sulphonamide-susceptible E. coli strain when treated with sulphaquinoxaline (200 mg/liter), sulphadimidine sodium (2 gram/liter), sulphachloropyridazine 30 per cent (1 gram/liter) and to a lesser degree sulphadiazine sodium (250 mg/liter). Synergism was demonstrated between trimethoprim and sulphadiazine (1:5). The combination of trimethoprim with sulphaquinoxaline (1:3) did not induce better therapeutic effects than sulphaquinoxaline in proportional doses. However, significant synergism was demonstrated between trimethoprim and both sulphonamides in treatment of experimental infection with sulphonamide-resistant E. coli. No signs resembling sulphonamide intoxication were observed during these studies.

Treatment of experimentally induced colibacillosis in broilers with doxycycline hyclate through the drinking water was just effective at a dose of 200 mg/kg body weight (1000 ppm). The achieved therapeutic effects were similar to those of tetracycline at the same dose and of flumequine at a dose of 19 mg/kg body weight (100 ppm).

In two experiments newly hatched broilers were orally inoculated either with intestinal microfloras cultured under different conditions or with a suspension of intestinal homogenate and challenged with high doses (3 X 10(5) c.f.u. per chick) of Salmonella infantis organisms. Inocula were prepared from intestinal material of mature SPF WL hens under aerobic or strictly anaerobic conditions (less than 5 ppm oxygen), and protected against atmospheric oxygen during storage. A very significant reduction of the number of Salmonella infantis bacteria in caecal content was achieved one and two weeks after challenge in those groups of chicks which were inoculated with anaerobically cultured flora or with intestinal homogenate. In order to induce protection, obligate anaerobes had to be accompanied by facultative anaerobes. Amprolium or Monensin dit not interfere with protection. Protection induced by intestinal microflora depends on anaerobiosis during preparation, culturing, storage, and application of the protective bacteria. Starvation on the first day of life appeared to have a negative effect on protection.

In contrast with the recommended dose of 2,000 ppm sulphadimidine sodium in the drinking water for treatment of broilers against colibacillosis, it appeared that under experimental conditions, treatment at 500 ppm (60 mg/kg body weight) gave the best therapeutic effects. At higher concentrations, drinking water consumption and body weight gain were reduced significantly. During treatment high blood plasma-concentrations were measured.