A field trial was done on a combination of oxytetracycline (continuous feeding at 250g/ton of feed over a period from to 60 weeks of age) and doxycycline (intermittent 5-day-administration, 15 times until 60 weeks of age) in 20 flocks of 11 layer breeder farms (in 8 prefectures) and 19 flocks of 13 broiler breeder farms (in 9 prefectures). The 24 farms had been suffering from Mycoplasma gallisepticum (MG) and M. synoviae (MS) infection and treated mainly with tylosin or other macrolide antibiotics.
The combination program was compared with those conventional programs of each 39 flocks as controls on the results of serum inspection and performance data.
The combination kept 37 flocks (95%) MG- and MS-free, but only 2 flocks (5%) were kept in the controle unitl 60 weeks of age. It showed a better performance in terms of hen housed eggproduction which was 8.4 and 10 eggs in layer- and broiler-breeder flocks, respectively, over the conventional programs. Hatchability was also improved 1.5% and 1.8% in the respective flocks without any side effects. Those perfbrmances were as good as those of the standards of each strain.
In conclusion, the combination was applicable safely and effectively to the field condition for the prevention of Mycoplasma infection.