Invasion of chicken intestinal epithelial cells by Eimeria species causes one of the costliest diseases that affects the poultry industry worldwide. To reduce economic losses caused by the seven species of Eimeria, anticoccidial drugs have been used in 60% to 99% of chicken herds [1, 3]. Due to the emergence of drug-resistant parasites and increasing public concern regarding the presence of drug residue in chicken products, vaccines, probiotics and natural products have been considered as potential alternatives for coccidiosis control [9, 11, 17-18]. Although the effectiveness of these alternatives has been evaluated in commonly assessed parameters, such as body weight gain, intestinal lesion score, or fecal oocyst shedding [16, 18-20], few studies have included these parameters when evaluating Eimeria-infected birds [15, 21-22]. Therefore, the present study aimed to compare the aforementioned parameters in broiler chickens infected with three major Eimeria species, including E. acervulina, E. maxima and E. tenella.
Due to the lack of information regarding the dependence of sex on avian coccidiosis, in our first experiment we carried out a sex-based evaluation of the parameters using normal and E. tenella-infected broiler chickens. These data demonstrated a fundamental difference between the sexes with respect to body weight gain in both normal and E. tenella-infected broilers. However, no significant difference between the sexes was observed in lesion scores or fecal oocyst production in E. tenella-infected broilers (Fig. 1). Similarly, after E. acervulina and E. tenella infections, the chickens showed significant sex differences only in initial and final weight gain, but not in lesion scores, mortality, or packed red cell volume [23]. Furthermore, significant differences in body weight gain were observed between male and female broiler chickens challenged with E. maxima. However, there were no significant sex effects on fecal oocyst shedding or plasma carotenoid concentration measured 6 and 9 days post infection [24]. Generally, plasma carotenoid values were inversely related to the Eimeria oocyst inoculation dosage. Decreases in total plasma carotenoid coincided with significant reductions in the lesion score of E. tenella-infected broilers [24-25]. In our sex-based evaluation of body weight gain, intestinal lesion score, and fecal oocyst shedding in broilers infected with 1×104 sporulated oocysts of E. acervulina, E. maxima or E. tenella, the patterns of these parameters in infected females were similar to those of the infected males. Taken together, these findings indicate that the sex of Eimeria-infected broilers should be taken into account for experiments that include body weight gain as a parameter.
Broilers infected with 1×104 and 7×104 oocysts of E. maxima exhibited mean lesion scores of 0.8 and 2.8, respectively, and their body weight gains were significantly decreased compared with the uninfected birds (Fig. 2, 3, and 4). Similarly, when two genetic lines of broiler chickens were infected with E. acervulina, E. maxima and E. tenella, only E. maxima-infected broilers showed decreased body weight gains as compared with control broilers [26]. Generally, higher inoculation doses of E. maxima resulted in a lower body weight gain compared to lower inoculation doses [24, 27]. In broiler chickens infected with E. maxima, broilers with a higher lesion score (2.39) lost more body weight than broilers with a lower lesion score (1.72) [28]. However, Chasser et al. reported that weight gain in Ross broilers infected with E. maxima on day 14 after hatching, with a macroscopic lesion score of 0.9 (assessed on day 19), was similar to that of uninfected birds [15]. Additionally, for broilers inoculated with three isolates of E. maxima, each having different pathogenicity, there was no relationship between microscores and body weight gain on day 6 post infection [21].
In our study, broilers infected with 1×104 sporulated oocysts of E. acervulina and E. tenella had mean lesion scores of 1.8 and 2.2, respectively, and showed a similar body weight gain compared to uninfected birds. Broilers infected with a higher dose of E. acervulina and E. tenella had mean lesion scores of 3.1 and 3.6, respectively, and showed significantly decreased body weight gain compared to uninfected birds. Similar to the present results, E. tenella-infected broilers with lesion scores less than 2 had similar body weight gain compared to the uninfected control group, whereas infected broilers with lesion score of 3.5 showed significantly reduced body weight gain [29]. It is interesting to note that, for most outbred lines of chickens infected with E. tenella, decreases in body weight gain were greater in birds with lesion scores of 4 than those with lesion scores of 3, which indicated some correlation between lesion score and body weight gain [30]. Additionally, a correlation between body weight gain and lesion scores of approximately 3 was observed in 12 major histocompatibility complex congenic lines of chickens infected with E. tenella [31].