The efficacy and economic benefits of Paracox, a live attenuated anticoccidial vaccine, in commercial trials with standard broiler chickens in the United Kingdom.

The first large-scale broiler trials under modern commercial conditions of Paracox, a live attenuated anticoccidial vaccine administered in the drinking-water, are reported from the United Kingdom. The vaccine, comprising all seven of the species of Eimeria that parasitise the domesticated fowl, was compared with anticoccidial drug shuttles (halofuginone then salinomycin, or nicarbazin then monensin) in nine trials comprising over 936000 chickens, all of which also received the digestive enhancer virginiamycin. No clinical diseases were diagnosed in vaccinated birds in any of the trials. Necrotic enteritis occurred in the medicated controls (anticoccidial drug shuttles) of 2/9 trials and coccidiosis occurred concurrently with one of these outbreaks. Using additional criteria that particularly reflected economic benefits, the vaccine performed overall at least as well as the drug shuttles. The crucial results for vaccinated and medicated birds were: feeding costs (pence per kg liveweight of birds that were processed), 33.9 pence (vaccinated) and 33.7 pence (medicated) (P=0.549); feed conversion ratios, 2.01 (vaccinated) and 1.96 (medicated) (P=0.025); coefficient of variation in mean bird weight before processing, 9.3% (vaccinated) and 9.0% (medicated) (P=0.300); birds found dead, 3.0% (vaccinated) and 3.8% (medicated) (P<0.001); culled birds 4.0% (vaccinated) and 3.8% (medicated) (P=0.483); birds rejected during processing, 1.1% (vaccinated) and 1.2% (medicated) (P=0.271). In addition, the mean total water consumptions per chick were 7.82 L (vaccinated) and 7.76 L (medicated) (P=0.611), whilst the mean percentages of dry matter in the litter were 76.2% (vaccinated) and 75.2% (medicated) (P=0.195). Accumulation of oocysts in the litter of chicks vaccinated at 5 days of age peaked at 21 and 35 days, compared with medicated controls which showed a single higher peak at 35 days. Hence, the use of Paracox vaccine may control clinical coccidiosis in broilers and also achieve performances at least equal to anticoccidial drugs, particularly where drug resistance might result in failure to control disease.