Safety of the attenuated anticoccidial vaccine ‘Paracox’ in broiler chickens isolated from extraneous coccidial infection

Abstract

A trial was carried out in 1-day-old broiler chicks raised for 54 days in floorpens under simulated commercial conditions, but isolated from all extraneous virulent coccidial infections, to demonstrate the safety of 'Paracox' attenuated vaccine administered at the recommended dose when chicks were 7 days old. The vaccine did not adversely affect the water consumption, faecal moisture or litter condition of the broilers. Recycling of the attenuated coccidia occurred in vaccinated birds, oocysts being present in the litter between 5 and 33 days after vaccination; a single peak of oocysts was detectable 5 or 12 days after vaccination. Unvaccinated medicated control birds did not produce oocysts, indicating freedom from both between-pen contamination by the vaccine and invasion of the chicken-house by extraneous coccidial infection. A small proportion (4%) of vaccinated birds had mild coccidial lesions when sampled at 26, 33 or 40 days after vaccination. Despite this, the vaccinated birds performed better than control (unvaccinated, nicarbazin-treated) birds and there was no post-vaccinal check in their weight gain. Their mean finishing weight was 10.4% greater, their food conversion ratio 7.2% lower and their mortality 44.4% lower than the unvaccinated control birds, reflecting the safety of 'Paracox' vaccine.

The origins and biological significance of the coccidial lesions that occur in chickens vaccinated with a live attenuated anticoccidial vaccine

“…The higher proportion (24%) of sampled birds found to have lesions, compared with the 4% reported by Williams (1994), is probably accounted for by the fact that sampling was carried out daily in the present experiment, but only on three separate weekly occasions in the previous study. The combined results of the two experiments show that secondary lesions may occur in broilers up to at least 40 days after vaccination with Paracox vaccine.…”

“…However, lesions have been seen in commercial chickens vaccinated with Paracox (Schering-Plough Animal Health, Harefield, UK) (for example, Bushell et al, 1990;Bushell, 1992;Shirley et al, 1995), but in all but one case it was unclear at the time whether they were due to the attenuated vaccine per se or to a wild-type challenge. The first clue was the identification of mild lesions, in 4% of 150 broilers vaccinated with Paracox, between 26 and 40 days after vaccination in a floor pen trial in a facility protected from extraneous coccidial infections (Williams, 1994). A confirmatory experiment to establish whether vaccination with attenuated coccidia can give rise to lesions without any additional challenge from extraneous parasites is the subject of this paper.…”

Comparison of an attenuated anticoccidial vaccine and an anticoccidial drug programme in commercial broiler chickens in Italy

“…Wet litter may result from subclinical necrotic enteritis, not seen in these trials but often observed in broilers in northern Europe, even when antibiotic growth promoters and ionophore anticoccidial drugs are used (Williams et al, 1999). The final litter moisture contents observed in these Italian trials (18.5 to 21.0% after 36/37 days; 20.6 to 22.9% after 56 days) (Table 3) were generally a little lower than the means of 25.8% (Williams, 1994) and 24.3% (Williams et al, 1999) obtained in trials in the cooler temperate climate of the UK.…”

Recent Advances in Biology and Immunobiology ofEimeriaSpecies and in Diagnosis and Control of Infection with These Coccidian Parasites of Poultry

“…An advantage of attenuated vaccines is that they have low reproductive potentials, thus avoiding crowding in the specific mucosal areas of infection and resulting in the development of optimal immunity with minimal tissue damage (105). It is believed that the drug-sensitive, attenuated strains and wild, native strains interbreed, reducing both virulence and drug resistance in local populations.…”