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Vaccination: It only gets better

Ideally, he wanted something that would give his tiring, in-feed anticoccidials a much-needed rest while preparing him for the day when drug-free solutions might be the only desirable option for coccidiosis control.

More than 5 years later, the veterinarian and production manager for Grupo Sada pa Valencia — Spain’s largest broiler producer, with more than 50 million broilers a year — says the returns from coccidiosis vaccination have far exceeded his expectations.

“Our aim was only to prevent coccidiosis, without expecting to improve performance parameters,” Bellés recalls. “However, the benefits of vaccination have proved to be much greater than we ever anticipated.”

Besides showing significantly lower mortality than medicated birds, flocks vaccinated for coccidiosis have also yielded improvements in feed-conversion ratio (FCR), average daily gain (ADG), European efficacy index (EEI) and carcass uniformity.


The improvements did not occur overnight, however.

During the first year, Grupo Sada used the coccidiosis vaccine in randomly selected broiler flocks and only for one cycle before returning to in-feed anticoccidials. No performance improvements were seen when the vaccine was used in this manner, Bellés says. In fact, mortality rates increased and feed conversion decreased slightly, while daily gain also declined.

“We knew it wasn’t the vaccine’s fault, so we started to analyze the reasons for not finding any favorable differences in performance,” Bellés says. “We concluded that vaccination is not something that can be started and stopped at random. To really evaluate the vaccine, we needed to use the vaccine continuously — at least for a few consecutive cycles — and set up trials with a pre-defined schedule.”

Why consecutive cycles? The vaccine, Paracox-5*, contains a controlled, balanced dose of Eimeria organisms that stimulate the flock’s natural immunity to coccidiosis.

Chicks ingest and shed the vaccinal organisms, which multiply in the litter and become ingested and shed again. This process not only builds immunity to coccidiosis, but it also helps to replace populations of more aggressive field strains of Eimeria organisms that may have “leaked” through control programs used in medicated flocks. The early cycling of the vaccine also helps reduce carryover of Eimeria organisms, which lowers the level of coccidiosis challenge in subsequent flocks.

For this reason, it’s common for performance of vaccinated birds to improve with each flock and often surpass that of medicated birds, which often experience subclinical coccidiosis late in their life cycle. “We had been having some problems with coccidiosis outbreaks, but we were more concerned with subclinical coccidiosis,” Bellés adds. “The medications were not as effective as they were in the past.”


In 2007, Bellés initiated what would eventually become an intensive 4-year trial comparing the performance of vaccinated and medicated birds. Paracox-5 was used continuously for three cycles, followed by traditional regimens of in-feed anticoccidials in the next two cycles. All medicated birds received nicarbazin and narasin in the starter ration. In winter, Bellés used monensin in the grower diets and, in summer, used either lasalocid or robenidine followed by lasalocid.

As part of the extensive trial, Bellés also monitored subclinical coccidiosis, which he says is “a big problem” in medicated broiler flocks, especially after 35 to 40 days. “When farm veterinarians sometimes do necropsies, they generally don’t do them late in the growing cycle, so they are not aware that subclinical coccidiosis is a problem,” he explains. “For this study we were posting birds after 40 days. Just last week, we saw coccidiosis in birds that we didn’t think had a problem.”

To reduce variables and make results more meaningful, Bellés limited the trials to farms in the same geographic area (southeastern Spain) — all with the same genetics, hatcheries, feed, stocking density (37 kg or 81.5 lbs per square meter), management personnel, veterinary technicians and health programs for other poultry diseases. Bellés also eliminated seasonal and weather variables by trying all vaccine and medication protocols in all seasons at all farms.

“The idea was to have approximately the same number of vaccinated flocks every month, with all farms going on and off the vaccine every three cycles,” Bellés says. “This way, on a monthly basis, we always had vaccinated and non-vaccinated farms. That was the big difference between the first year (2006) and 2007 through 2010.”


The only unavoidable variable resulted from the local practice of thinning flocks. About 25% of Grupo Sada’s females, usually weighing 1.85 kg (4.07 lbs) at 35- 36 days, are marketed ahead of the faster growing male birds and remaining females.

In the early years of the study, no zero-withdrawal anticoccidials were available in this market, so the birds targeted for thinning had to be given a drug-free diet a few days before marketing. The remaining birds stayed on medicated feed until 42 days and were sent to processing at 47-48 days when they weighed 2.6- 2.7 kg (5.7-5.9 lbs). This variable was eliminated in 2010 after withdrawal times for some anticoccidials were reduced to zero days, which allowed thinned birds to stay on the same medicated “phase 3” feed (31-42 days) as the other birds.

Bellés does not think this minor change significantly affected the outcome of the trial, which was conducted on 165 farms and involved more than 71 million birds (25.8 million vaccinated, 45 million medicated). “Even though the trial did not include a statistical design, the amount of birds is extremely meaningful,” he says.


Because Bellés saw “major discrepancies in 2006 results” that resulted from using the vaccine at random and for only one cycle, he chose to focus only on performance data from 2007 through 2010. His conclusions:

Flocks vaccinated with Paracox-5 showed a 9% drop in mortality rate compared to medicated birds (Figure 1).

The FCR of vaccinated birds was 1.18% (20 g) better than medicated flocks (Figure 2). “This might look only minor at a glance, but this 20-gram improvement in these millions of birds represents more than €30 million ($40.6 million) over this 4-year period,” the veterinarian reports.

Vaccinated birds showed a slight improvement in ADG (Figure 3). “This is somehow surprising, in a good way, since we always expected a lower weight gain in vaccinated chickens due to the vaccine oocyst cycling/replication at 18, 19 and 20 days of age,” Bellés says.

The European production efficacy factor (EPEF) of the vaccinated birds was 2.47% better than the birds medicated for coccidiosis (Figure 4).


Digging deeper into the performance data and dividing results into four tiers of performance — top 25%, bottom 25% and two middle groups — Bellés uncovered even more startling improvements in the vaccinated flocks.

For example, mortality rates among the top 25% were only slightly lower in vaccinates than in medicated birds. However, in the bottom 25%, vaccinates showed a 14% mortality rate improvement over birds receiving anticoccidials. “Don’t forget, the only major difference was the vaccine,” he says.

The vaccinates in the bottom 25% also showed 2.5% improvement in FCR over the bottom 25% of medicated birds. This pattern also carried over to ADG, where the gap between non-vaccinates and vaccinates was “abysmal,” Bellés says, referring to the 1.4% advantage for vaccinated birds.


“At the end, all performance indicators were better in the vaccinates than in the flocks treated with anticoccidials,” Bellés says. “Evaluations were measured and recorded every month. And while variations occurred, general results were consistent in all periods. Even though no statistical analysis was performed, we have seen a very small coefficient of variation in all results.”

Sooner or later, the veterinarian adds, raising antibiotic-free birds could potentially become mandatory in some markets.

“It’s something we have to think about,” he says, while unleashing several thought-provoking questions to ponder.

“Will the ionophore-resistance issue become more important? Very probably,” he continues. “Can the rotation of vaccines and anticoccidials help control this resistance? We have seen this already, but what are the other benefits? Will a vaccine for necrotic enteritis help? We will see in 2012 and beyond. I am convinced that the future of poultry disease control is not in [the continuous feeding of] antibiotics; the future is in immunology.”

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