Reasons for Field Problems with Eimeria maxima:
E. acervulina versus E. maxima
Greg F. Mathis, Southern Poultry Research, Inc.
The three most commonly occurring species of Eimeria
infecting chickens are Eimeria acervulina, E. tenella, and E. maxima. Even
though E. maxima is very immunogenic, lesions are often observed in the field
late in a growout. A survey of 50 coccidial field isolates showed that 36 were
predominately E. acervulina, 4 E. maxima, and 10 E. tenella. All of the E.
maxima isolates came from farms where the broilers were over 28 days old. Most
of the E. acervulina isolates were from broilers that were 18 to 28 days old.
The daily oocyst shedding pattern for a commercial coccidial vaccine was
examined in floorpen birds. Birds vaccinated for coccidiosis at the hatchery
were placed into pens on new pine shavings. The shedding of E. acervulina type
oocysts peaked around 18 days. A small peak of E. maxima was observed around 28
days. A battery cage study was conducted to examine whether E. acervulina could
be interfering with E. maxima development. Birds were challenged at 14 days of
age with E. acervulina and/ or E. maxima. The oocyst per bird challenge levels
were none (Trt. 1), E. acervulina 100,000 (Trt. 2), E. acervulina 100,000 plus
E. maxima 5,000 (Trt. 3), E. acervulina 50,000 plus E. maxima 5,000 (Trt. 4), E.
acervulina 25,000 plus E. maxima 5,000 (Trt. 5), and E. maxima 5,000 (Trt. 6).
Each treatment consisted of 3 replications in a complete randomized block
design. E. maxima alone caused 21 % weight reduction and 2.75 lesion score. The
100,000 and 50,000 E. acervulina oocyst level reduced E. maxima lesions to 1.33.
The 25,000 E. acervulina oocyst level only slightly reduced E. maxima lesions to
2.25. The E. maxima did not interfere with any of the E. acervulina infections.
This study suggests that E. acervulina interferes with colonization or
development of E. maxima. As birds become more immune to E. acervulina, then E.
maxima has more of an opportunity to develop.