PSIII-5 - Effect of Graded Eimeria Vaccine Challenges on Broiler Chicken Performance

Abstract: Infection with apicomplexan parasites of the genus Eimeria causes damage to gastrointestinal epithelial cells and increases the malabsorption of nutrients in broiler chickens, resulting in depressed performance and economic loss. The objective of the study was to evaluate the effect of graded Eimeria vaccine challenges on growth performance, oocyst shedding, and plasma carotenoid levels. A total of 140 one-day-old Cobb 500 broiler chicks (55.49 ± 2.55 g BW) were housed in environmentally controlled Petersime battery brooders with modified wire floors, containing 5 birds per pen with 7 replicate pens per treatment. Pens were randomly assigned to one of 4 treatments: a negative control and three positive treatments that received 15×, 20×, or 25× the recommended vaccination dose. At ten days of age, positive treatment birds orally received the ADVENT^® coccidiosis vaccine containing unattenuated strains of Eimeria acervulina, Eimeria maxima, and Eimeria tenella. Body weight, average daily gain, feed intake, and feed conversion ratio were determined after 10, 15, and 20 days (d) of age. On d 15 and 20, one random bird per pen was bled for plasma carotenoid analysis and feces from each pen was collected for oocyst quantification. Body weight, average daily gain, and feed conversion ratio were significantly depressed (P < 0.05) among all positive treatments when compared with the negative control on d 20, but no treatment effect on feed intake was observed. Similarly, birds in positive treatment groups had lower (P < 0.05) plasma carotenoid levels and higher (P < 0.05) oocysts per gram of feces than the negative control on d 20. No differences were observed in performance, plasma carotenoid levels, and fecal oocysts among treatments on d 15. These results indicate that 15, 20, or 25 doses of the ADVENT^® vaccine can be used to replicate subclinical coccidiosis in broiler chickens.