The effect of increased crude protein level and/or dietary supplementation with herbal extract blend on the performance of chickens vaccinated against coccidiosis

The experiment was designed as a 2 × 2 × 2 factorial arrangement with 6 replicate pens per treatment (8 male Ross 308 chicks per pen) conducted from 1 to 42 d of age to evaluate the effect of dietary crude protein level (CP) and herbal extract blend on performance indices, results of slaughter analysis, and oocyst shedding in broilers vaccinated against coccidiosis. Treatments included a lack or single dose of live anticoccidial vaccine (Livacox T®, administered at 1 d of age, VAC), normative (21.6 and 20% in the starter and grower-finisher feeding phase, respectively) or increased (23.6 and 21.6% in the starter and grower-finisher feeding phase, respectively) dietary crude protein level, with or without supplementation with an herbal extract blend (Echinacea purpurea, Salvia officinalis, Thymus vulgaris, Rosmarinus officinalis, Allium sativum, Origanum vulgare; HE, 0 or 2 g/1 kg of feed). Each dose of vaccine contained 300-500 sporulated oocysts of each Eimeria acervulina, E. maxima and E. tenella which are specific to different sections of the intestinal tract. Wood shavings as a bedding guaranteed vaccine oocyst recirculation. A negative effect of VAC on FI, BWG or FCR (P < 0.05) was found in the starter feeding phase and remained noticeable (P < 0.05) till the end of the rearing period. There was no significant effect of CP or HE on performance in the starter feeding phase period. The increased CP level decreased fat deposition in the carcass and improved the BWG (P < 0.05) of vaccinated birds in the second and entire experimental period, while HE positively influenced the 1-42 FCR (P < 0.05) in vaccinated birds. The dietary treatment did not interfere with recirculation of the vaccine's oocysts, which is necessary for building up immunity. It can be concluded that an increased CP level or HE supplementation may be considered as support tools in terms of vaccination.