The effect of monensin on the immunity arising from repeated low-level infections with Eimeria maxima, E. brunetti and E. tenella.
A study was made of the effect of monensin on the development of immunity to E. maxima, E. brunetti or E. tenella in chickens given repeated inoculations of oocysts. Birds were inoculated three times weekly with either 1000, 100 or 10 oocysts for a total of 13 inoculations. Faecal oocyst output was recorded throughout the experiment, and after 33 days, birds were challenged with 100,000 oocysts of each species. Whereas non-medicated birds given the schedule of 10 oocysts of E. maxima had a patent period of 12 days the duration of patency for E. brunetti and E. tenella was considerably extended. Exposure of non-medicated birds to a total of only 130 oocysts over a 28-day period resulted in a strong immunity to E. maxima and E. brunetti but protection against E. tenella was incomplete. Development of immunity in birds fed 125 parts per million monensin was dependent upon the number of oocysts administered. With the exception of the group receiving the repeated dose of 10 oocysts of E. maxima, monensin did not suppress oocyst production completely. Immunity developed in medicated birds given 100 oocysts of E. maxima or 1000 oocysts of E. brunetti Partial immunity appeared in medicated birds given 100 oocysts of E. brunetti or E. tenella. Whether sufficient coccidial development would occur to stimulate immunity in practical situations would depend upon the frequency and intensity of exposure to infective oocysts in the environment.
Chapman
H D
HD
Houghton Poultry Research Station, Houghton Huntingdon, Cambs., England.