Meta-analysis of the performance variation in broilers experimentally challenged by Eimeria spp.

A meta-analysis was carried out to (1) study the relation of the variation in feed intake and weight gain in broilers infected with Eimeria acervulina, Eimeria maxima, Eimeria tenella, or a Pool of Eimeria species, and (2) to identify and to quantify the effects involved in the infection. A database of articles addressing the experimental infection with Coccidia in broilers was developed. These publications must present results of animal performance (weight gain, feed intake, and feed conversion ratio). The database was composed by 69 publications, totalling around 44 thousand animals. Meta-analysis followed three sequential analyses: graphical, correlation, and variance-covariance. The feed intake of the groups challenged by E. acervulina and E. tenella did not differ (P>0.05) to the control group. However, the feed intake in groups challenged by E. maxima and Pool showed an increase of 8% and 5% (P<0.05) in relation to the control group. Challenged groups presented a decrease (P<0.05) in weight gain compared with control groups. All challenged groups showed a reduction in weight gain, even when there was no reduction (P<0.05) in feed intake (adjustment through variance-covariance analysis). The feed intake variation in broilers infected with E. acervulina, E. maxima, E. tenella, or Pool showed a quadratic (P<0.05) influence over the variation in weight gain. In relation to the isolated effects, the challenges have an impact of less than 1% over the variance in feed intake and weight gain. However, the magnitude of the effects varied with Eimeria species, animal age, sex, and genetic line. In general the age effect is superior to the challenge effect, showing that age at the challenge is important to determine the impact of Eimeria infection.