In a laboratory trial chickens were given immunising doses of six species of Eimeria when they were 2 weeks of age and the effect of medication with
monensin or
arprinocid from 0-10 weeks was determined by challenge inoculation.
Monensin in the food at 60-100 ppm resulted in depression of immunity but concentrations of 40-50 ppm only slightly affected immunity to challenge inoculation.
Arprinocid at 50 ppm also greatly reduced the development of resistance to
infection but 20 ppm did not. In a field experiment where chickens were exposed only to naturally occurring coccidial populations, the feeding of
monensin (45 ppm) or
dinitolmide (125 ppm) for 14 weeks did not affect the development of immunity to the indigenous coccidial populations.
Monensin-treated birds appeared to be slightly better protected. Chickens treated with
monensin reached their target
body weight earlier and maintained it better than
dinitolmide-treated chickens. Large numbers of oocysts were present in the litter of birds treated with
dinitolmide. Oocyst numbers reached a peak at 3 weeks and remained high until the birds were 10 weeks of age. Treatment with
monensin at 45 ppm resulted in low oocyst counts in the litter until skip-a-day treatment was initiated. It is concluded that the inclusion of
monensin at 40-50 ppm in the food may be suitable for the rearing of replacement chickens.