Evaluation of coccidial-infection levels among flocks in the US shows that coccidiosis vaccination induces early and mild coccidial cycling — an especially relevant finding considering the soaring cost of feed, Dr. Matilde Alfonso said.

“The results of the study demonstrate that poultry producers can use coccidiosis vaccination to change the timing, prevalence and severity of coccidiosis challenge and also to reduce feed costs,” she said.

Alfonso, a technical service veterinarian with Intervet/Schering-Plough Animal Health, said the study encompassed over 2,500 broilers from four different US commercial operations in different states. Birds ranging from 14 days to market age were examined for coccidial lesions during necropsy. The prevalence and severity of the lesions were considered, as well as the time they occurred.

The necropsies were conducted by technical service veterinarians from Intervet/Schering-Plough Animal Health, and primarily by Alfonso.

Alfonso used the well-known Johnson and Reid method to score gross lesions due to the common coccidial species Eimeria acervulina, E. maxima and E. tenella. There are some limitations when using lesion scores alone to assess flock performance or the efficacy of an anticoccidial program, Alfonso added, but it is a widely used method in the field for monitoring coccidiosis in commercial broiler operations. When performed consistently, lesion scoring allows comparisons over time and between different coccidiosis-control programs.

In addition to gross-lesion scoring, Alfonso and her colleagues microscopically examined mucosal scrapings from the mid-intestine to assess the presence of E. maxima oocysts. While other Eimeria species such as E. acervulina and E. tenella can usually be diagnosed by observing gross lesions with the naked eye, E. maxima is different, Alfonso explained.

“E. maxima can be there in high numbers, damaging the intestinal lining and negatively affecting bird performance without causing visible lesions. That’s why we always determine the presence of E. maxima with the microscope, as well as by gross-macroscopic inspection. We score the findings based on how many oocysts we see per microscopic field,” she said.

The most obvious result in the study was that the prevalence and severity of coccidial lesions and the time they occurred varied with the control program used — early in vaccinated birds and later in birds receiving in-feed anticoccidials, the veterinarian said.

At a major poultry company in South Carolina, where a traditional in-feed anticoccidial shuttle program was rotated with coccidiosis vaccination, birds on the shuttle program experienced late coccidial cycling from 5 to 7 weeks (35 to 49 days) of age. But after coccidiosis vaccination was initiated, cycling occurred at 3 to 4 weeks (21 to 28 days) of age, Alfonso said (see Figure 1).

The importance of early coccidial cycling is underscored by studies conducted at Oklahoma State University by Dr. Robert Teeter and associates (see article, page 39). Those results show that the later in life birds experience coccidial cycling, the greater the impact on performance — and on the producer’s bottom line, Alfonso said.

In other words, if coccidial cycling occurs before the bird’s major growth spurt, which occurs after 4 weeks (28 days) of age, it is less likely to interfere with growth at a time when birds are consuming the most feed, she said.

At the same South Carolina company, vaccinating with Coccivac-B — a live vaccine that provides a controlled, balanced dose of coccidial oocysts to stimulate immunity — restored sensitivity to ionophore anticoccidials by seeding the poultry houses with drug-sensitive strains, Alfonso noted.

Tracking at the South Carolina company further demonstrated that inconsistent coccidial cycling occurs when ionophore anticoccidials alone are used, Alfonso said.

Alfonso also discussed a poultry company in Mississippi, which rotated in-feed anticoccidials with coccidiosis vaccination. Over a 5-year period beginning in 2001, extended vaccine use led to a low occurrence of E. acervulina gross lesions and decreased the severity of lesions. The occurrence and severity of E. maxima microscopic lesions also declined, Alfonso said.

In Alabama, where a poultry company used coccidiosis vaccine continuously following a traditional control program with in-feed medications, the occurrence and severity of lesions declined with time.

Coccidial cycling occurred earlier and the birds consistently had immunity by 5 weeks (35 days) of age (see Figure 2), Alfonso said.

The impact of coccidiosis vaccination following an ionophore program was also evident at a company in Arkansas. Four months after initiating vaccination, the number of birds with coccidial lesions declined, coccidial cycling occurred at 3 to 4 weeks (21 to 28 days) of age, and birds had consistent immunity by 5 weeks (35 days) of age, she said.

Similar results were achieved at the Arkansas company when coccidiosis vaccination in antibiotic-free birds was compared to the continuous use of anticoccidial drugs in conventional birds. Vaccinated birds had earlier cycling and immunity plus fewer lesions compared to birds on the drug program, Alfonso said.

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