Relationship of E. acervulina Ionophore Resistance to Field Problems with E. maxima
Greg F. Mathis, Southern Poultry Research, Inc.
An earlier
study suggested that E. acervulina can interfere with colonization of E. maxima.
The object of this study was to examine the relationship of E. acervulina
sensitivity to Salinomycin and subsequent infection level with E. maxima. A
battery cage study was conducted. Birds fed nonmedicated or Salinomycin 60 g/t
feed were challenged with either a Salinomycin sensitive, resistant strain of E.
acervulina and/or an E. maxima field isolate. The oocyst per bird challenge
levels were none; E. acervulina (sensitive); 50,000, E. acervulina 50,000 (resistant);
E. acervulina 50,000 (sensitive) plus E. maxima 5,000; E. acervulina 50,000 (resistant)
plus E. maxima 5,000; or E. maxima 5,000. E. maxima alone caused 20 % weight
reduction and 2.70 lesion score. Salinomycin controlled the sensitive strain
with 5 % weight reduction and 1.25 lesion score. Salinomycin did not control the
resistant strain, with 22 % weight reduction and 2.75 lesion score. The birds
infected with E. maxima and sensitive E. acervulina had E. maxima lesion scores
of 2.25. The birds infected with E. maxima and resistant E. acervulina had E.
maxima lesion scores of 1.30. From the results it can be inferred that E.
acervulina interfered with development of E. maxima. Higher anticoccidial
resistance allows more E. acervulina colonization, which appears to interfere
with colonization of E. maxima, and thus indirectly slows E. maxima immunity
development. This increases chance for late problems with E. maxima, possibly
explaining an increase in field reports of late E. maxima infections where
Salinomycin has been extensively used.