Evaluation of the efficacy of Eimeria maxima oocyst immunization with different strains of day-old broiler and roaster chickens.

The performances of three different strains of male and female broiler or roaster chickens immunized at 1 day of age with a drug-resistant field isolate of Eimeria maxima were evaluated in battery and floorpen immunization trials. No difference in immunization potential was seen between these strains or sexes of day-old chickens immunized with 2500 oocysts/bird of E. maxima and challenged at 10 days of age with 25,000 oocysts/bird of the same isolate in two separate battery trials. All immunized birds showed significant protection for the parameters of weight gain and midintestinal lesion scores at 7 days post challenge (PC) when compared with nonimmunized challenged controls. In two separate floorpen trials, one broiler bird strain (designated strain 2) immunized by the same procedure and challenged at 21 days of age with the equivalent of 25,000 oocysts/bird of the same isolate showed significant protection for weight gain and lesion scores at 7 days PC when compared with nonimmunized controls. Birds in these same floorpen experiments immunized with E. maxima and then fed three different anticoccidial shuttle diets (narasin and nicarbazin 90 grams/ton (g/t) in starter feed and narasin 72 g/t + roxarsone 45.4 g/t in grower feed; nicarbazin 113 g/t in starter feed and narasin 72 g/t + roxarsone 45.4 g/t in grower feed; and monensin 100 g/t in starter and grower feed) showed no interference with elicited immunity with E. maxima challenge for the same parameters measured. No significant difference was seen between any floorpen immunized bird groups for total weight gain at trial terminations (49 days of age).