Analysis of disease resistance-associated parameters in broiler chickens challenged with Eimeria maxima

To determine an optimal dose for coccidial inoculation and to evaluate gene tic resistance or susceptibility in individual chickens, broilers were inoc ulated with four different doses of Eimeria maxima oocysts. Body weight gai n, fecal oocyst shedding, concentrations of plasma NO2- + NO3-, carotenoid, and interferon-gamma were measured at two different time periods postinfec tion. The results showed significant dose and sex effects on most parameter s and interaction between dose and sex in some parameters. The dose effects were generally linear; however, some significant quadratic effects were al so observed. The measurements from chickens inoculated with 10(4) oocysts d isplayed the highest correlation coefficients among oocyst shedding, body w eight gain, and concentrations of carotenoid and NO2- + NO3-. An infection index, calculated from the correlated parameters, displayed high correlatio n coefficients with the parameters. The infection index may be a better par ameter for evaluating individual genetic resistance against coccidial infec tion.