Comparison between a live, attenuated anticoccidial vaccine and an anticoccidial ionophore, on performance of broilers raised with or without a growth promoter, in an initially Eimeria-free environment

An experiment was carried out to study the effects of vaccination with Para cox((R)), a live, attenuated vaccine against avian coccidiosis, on broilers isolated from extraneous Eimeria parasites. The study involved 3200 broile r chickens raised in floor pens similar to commercial conditions, but in an initially Eimeria-free environment. Forty percent of the chickens were vac cinated at 3 days of age and given either a basal unmedicated feed or a fee d supplemented with the feed antibiotic virginiamycin. Unvaccinated birds w ere given either the basal feed or feed supplemented either with virginiamy cin or the anticoccidial ionophore narasin. At slaughter at 36 days of age vaccinated birds had a lower live weight than non-vaccinated birds. The dif ference was 4.6% in unmedicated, and 6.0% in virginiamycin medicated chicke ns. Feed conversion ratio at slaughter was 2.5% higher for unmedicated vacc inated birds, and 1.3% higher for virginiamycin medicated vaccinated birds, compared to respective non-vaccinated groups. There was no significant dif ference in overall performance of unvaccinated birds given narasin as compa red to virginiamycin. At 10 days post vaccination vaccinated birds had a hi gher number of Clostridium perfringens in the caeca, but there was no diffe rence thereafter. Throughout the experiment, caecal clostridial counts were considerably higher in vaccinated unmedicated birds than in unvaccinated b irds given narasin. The number of oocysts shed in the vaccinated groups was very low, but during a subsequent challenge with E. maxima and E. tenella the birds' immunity was found to be satisfactory.