A synergistic in-vitro interaction between tiamulin (THF) (Tiamutin - Novartis) and chlortetracycline (CTC) against avian mycoplasma has been reported (1). It was the purpose of this study to evaluate the efficacy in vivo of such a combination in preventing an experimentally induced Mycoplasma gallisepticum (MG) infection.
Materials and Method: One hundred and thirty 5-week-old broilers were allotted to 1 of 13 treatment groups (see Table 1). Groups 2-13 were infected with an intra-air sac injection of 0.2ml of a 24-hour old broth culture of MG (3x107 CFU/ml). The birds were then treated via the drinking water for 3 days and autopsied after a further 4 days. Air sac lesions were scored and cultured for MG. Weight gain and feed intakes over the 7 day trial period were recorded.
The results are summarised in Table 1 and Graphs 1 and 2.
Table 1. Summary of trial results
|Group||THF (ppm)||CTC (ppm)||MG infected||Air sac lesion score* (%)||MG re-isolation (%)||ADG (g)||FCE|
Graph 1. Comparison of air sac lesion scores following a M. gallisepticum artificial infection challenge and treatment with tiamulin and chlortetracycline alone and in combination
Graph 2. Comparison of M. gallisepticum re-isolation following an artificial infection challenge and treatment with tiamulin and chlortetracycline alone and in combination
Discussion and conclusions:
A substantial enhancement effect was demonstrated by the combination of THF and CTC in groups 12 and 13, giving an effect equivalent to tiamulin at 2.5-3 times lower concentration. Insufficient test concentrations of CTC were used to fully establish its effective end point but a previous report (Baughn et al, 1978) showed that 500-1000ppm was required to substantially reduce the number of birds with lesions, suggesting the combination increased the CTC effect by 4-5 times. The lower dosage rate of tiamulin used in the combination, whilst maintaining efficacy, should substantially reduce the risk of severe ionophore anticoccidial interactions occurring in poultry.
1. Burch, D.G.S. and Stipkovits, L. (1993) Enhanced effect of tiamulin and chlortetracycline or tiamulin and Doxycycline combinations against avian Mycoplasma. Proceedings World Veterinary Poultry Congress, Sydney, Australia, p167
2. Baughn, C.O. et al, (1978) Effect of tiamulin in chickens and turkeys infected experimentally with avian Mycoplasma. Avian Diseases, 22, 620-626
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