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"Synchronized coccidiosis control, management yield better broiler results"
Newman

Performance in broiler flocks can be improved by coordinating the coccidiosiscontrol program with management practices, Dr. Linnea Newman said.

Broilers perform better if they develop immunity against coccidiosis early rather than late into the production cycle. However, exactly when immunity develops varies with different anticoccidial programs and management practices, she said.

“For instance, flocks that are on reused litter in houses with higher bird density develop immunity earlier than flocks started on clean litter in a full house,” said Newman, of Intervet/Schering-Plough Animal Health technical services.

“Coccidiosis control in broilers depends upon immunity — regardless of whether in-feed medication or vaccination is used,” she said.

Early immunity against coccidiosis is preferable because the adverse effects of subclinical coccidiosis on performance worsen with age, she said.

Newman cited work at Oklahoma State University (see article, page 39), which demonstrated that the later in life broilers develop immunity to coccidiosis, the greater the negative impact on performance and the greater the cost.

This work is important, she explained, because “many coccidiosis-control programs, especially ionophores, shift the immunity-building process to the last 2 weeks of a broiler’s life — when the most significant weight is to be gained, the greatest amount of feed will be consumed and there is the greatest potential for a loss in performance.”

Oocyst counting and weight analysis on commercial broiler farms further confirm the link between late development of immunity and worsening performance — as well as the role of the anticoccidial and management programs used, Newman said.

Clean litter can delay immunity

“Surprisingly, cleaning out houses works against the immunity-building process, especially with in-feed anticoccidial programs, causing an even greater impact late in the life of a broiler,” Newman said. On anticoccidial programs, coccidial populations may explode after 28 days, with higher peaks and a greater potential for an adverse impact on broiler weight gain. In contrast, used litter exposes birds early in life to coccidia, which initiate the gradual development of immunity.

Actual oocyst counts from clean litter obtained in British Columbia and Ontario demonstrate the pattern of Eimeria spp.- oocyst shedding in full-house brooders where birds receiving various in-feed anticoccidials were started on clean litter with a mandatory 2-week (or greater) down time.

When the farm in Ontario collected oocysts and determined daily weight for one of its broiler flocks, the impact of a late subclinical coccidial challenge was evident, with weight diverging from the Ross 308 published breed standard (see Figure 1). “This is a real-world example of the model developed by the Oklahoma State University researchers,” Newman added.

Figure 1. Oocyst counts from clean litter versus the actual growth curve show divergence from the Ross 308 male 2007 breed standard. These birds received narasin.

Half-house brooding on reused litter produced different patterns. Higher bird density (<0.80 ft2/bird) and heavily reused litter from a farm located in the Delmarva Peninsula of the US produced an early oocyst peak at 19 days, regardless of whether the program was Nicarb-narasin or salinomycin, she said.

In contrast, birds that received salinomycin and were in houses with low bird density (1.0 ft²/bird), half-house brooding and reused litter produced a later pattern after two flocks; the pattern was similar to that found in clean houses.

Birds that are vaccinated against coccidiosis demonstrate some variability in the development of immunity, but the pattern is usually earlier than natural immunity programs utilizing anticoccidials, Newman said.

Vaccinated flocks started with half-house brooding on reused litter peaked at 19 days (see Figure 2). In contrast, vaccinated birds started in a full house on clean litter had a delayed peak at 25 days.

Figure 2. The oocyst peak in flocks vaccinated against coccidiosis with Coccivac-B and started in half-house brooding on reused litter was an early 19 days. Density was 0.80 ft²/bird.

Coccidiosis control with in-feed anticoccidials, Newman said, no longer provides complete “control” as it did 25 years ago when many of the products were introduced. “Most coccidiosis control in broilers today depends on immunity — either natural immunity moderated by anticoccidial drugs, or immunity developed through vaccination,” she added.

The successful development of immunity is moderated by management style: clean vs. reused litter, stocking density and house management, which all impact when and how immunity develops, she continued.

The development of immunity to coccidiosis requires exposure to multiple life cycles of Eimeria spp. This necessary exposure has an adverse impact on weight gain and feed conversion, but the impact will be a different magnitude depending upon where it occurs on the growth curve, Newman explained.

“If you want to maximize the geneticperformance potential of your broilers,” she said, “analyze your coccidiosis-control program to determine when immunity is completed on the growth curve and the consistency of that timing over the full production year.

“Coordinate your broiler-house management and coccidiosis-control programs to induce earlier immunity,” Newman concluded.

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