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Passive immunity a viable strategy for Canada's Dr. Neil Ambrose

Ambrose: 'Higher gut viscosity creates an ideal environment for C. perfringens.'

Those who know Neil Ambrose know that he's passionate about chicken production. In addition to growing chicken on his own farm located nearby Abbotsford, BC, Dr. Ambrose is the Director of Veterinary Services for Sunrise Farms, BC and Alberta. This is why he's constantly looking for management practices that are effective and economical and that also meet the challenges of an evolving industry and new market standards.

Currently, Ambrose is conducting trials on his farm to identify an alternative program to Canadian in-feed medications. This follows European regulatory changes to eliminate all in-feed medications. "Canadian regulations often follow what happens in Europe, so I want to be proactive and develop a program that can successfully grow chickens on a non-medicated feed basis," explains Ambrose.

After initial trials with disappointing results, Ambrose was introduced to a new strategy based on using Coccivac- B vaccine plus maternal antibody induced by an experimental vaccine developed by Schering-Plough Animal Health in order to tackle both coccidiosis and necrotic enteritis. He then initiated a two-flock trial with this new passive antibody strategy and got encouraging results that are now inspiring him to evaluate the program without any backup from in-feed medication.

Off to a rough start

Ambrose's first trial attempts to reduce dependency on in-feed medications focused on controlling coccidiosis. He replaced in-feed anticoccidials with Coccivac-B vaccine, while continuing to use an in-feed antibacterial for necrotic enteritis control. This program was applied for six consecutive trial flocks and achieved mixed results. Although clinical coccidiosis was controlled, each flock did experience outbreaks of mild necrotic enteritis that resulted in increased mortality and reduced daily weight gain. It's important to note that the traditional wheatbased ration given to birds during the trials probably had a negative impact on results because it usually predisposes birds to greater necrotic enteritis, and that each bout of necrotic enteritis coincided with a normal feed change.

Vaccine plus passive immunity:

a new vaccine approach After these six flocks, Ambrose returned to his regular in-feed antibacterial and anticoccidial program for three flocks. It was during this period that Schering-Plough Animal Health consulting veterinarian, Dr. Linnea J. Newman, learned of his trials and introduced him to a new strategy, which included Coccivac-B plus passive immunity from a new vaccine to control necrotic enteritis.

Recently registered for use in the U.S., this new necrotic enteritis vaccine is administered to the breeder hen, which then passes the antibodies on to the broiler chick, potentially eliminating the need for in-feed antibacterials. Ambrose's interest in developing a production program for control of coccidiosis and necrotic enteritis without the use of medicated feed made his farm an ideal candidate for Schering- Plough Animal Health to test progeny from flocks vaccinated with the new vaccine in addition to Coccivac-B vaccine.

Getting chicks off on the right foot

Sunrise Farms modified diets to ensure a good start and reduce the necrotic enteritis-causing bacterium in young chicks.

After a three-flock break, Ambrose initiated a two-flock trial with Coccivac-B and passive immunity from the new
vaccine developed by Schering-Plough Animal Health. Broiler chicks from vaccinated parents and carrying antibodies against necrotic enteritis were placed on Ambrose's farm. In the first two trials, he eliminated all in-feed anticoccidials but maintained a reduced level of in-feed antibacterials as insurance. "We kept a low level of antibacterial in the feed because I wasn't ready to risk pulling the plug completely on the first two trials," explained Ambrose.

With the adoption of the new passive immunity program, Ambrose also wanted to ensure the chicks got off to the best start possible. This is where his nutritionist Dan Moody of Ritchie Smith Feeds stepped in. "When you go the vaccination route there are a lot of management factors you need to consider," explains Moody. "Vaccines work to improve the birds' immune system by challenging them with the disease. The outcome provides birds with antibodies and the ability to stand on their own and perform well. But, there are other factors that contribute to good performance, and feed is one of them."

This fit well with Ambrose's disease management philosophy, which says that in addition to appropriate use of medications and vaccines, beating coccidiosis and necrotic enteritis also requires strict attention to diet and barn management.

Ambrose had been feeding a traditional wheat-based ration with in-feed medication for both coccidiosis and necrotic enteritis. With the new vaccine trial, Ambrose, working with Moody, modified the diet to ensure a good start and to reduce the chance of creating a gut environment which would foster the proliferation of Clostridium perfringens, the necrotic enteritis-causing bacterium.

A specific starter ration was developed by Moody to include the best available ingredients. The ration was more expensive than other standard starters, but would help ensure the broiler chicks got off to a healthier start, achieving a heavier seven-day weight.

The grower ration was also modified from a 100% wheat base to a 70:30 wheat:corn mix. "Wheat has been shown to predispose birds to greater necrotic enteritis because it changes the gut pH, increasing gut viscosity," explains Ambrose. "Higher gut viscosity creates an ideal environment for C. perfringens to grow, and increases the potential of necrotic enteritis development. Corn doesn't have this impact on gut viscosity, so we decided to formulate it into the diet."

When reformulating the diet, the goal was to include more digestible products that are better utilized by the birds. Feed components, such as protein, that are not totally utilized in a ration often end up in the lower gut, creating an optimal food source to support the growth of C. perfringens.

Moody and Ambrose also formulated the new grower ration to replace part of the soybean meal with highly digestible soybean concentrates, in order to reduce indigestible sugars. They also opted for higher quality meals to lower the overall protein content and reduce protein passage to the lower gut. "This new diet, in combination with passive immunity from the new trial vaccine is how we were tackling necrotic enteritis," he says.

Ambrose also firmly believes that effective coccidiosis control makes necrotic enteritis management easier. To ensure he receives the best Coccivac-B vaccine performance, Ambrose also refined application methods at Fraser Valley Chick Sales, the Sunrise Farms hatchery which supplies his chicks, to help optimize vaccine application. Working with Schering- Plough Animal Health rep Lionel Gibbs, Ambrose replaced the hatchery's single nozzle vaccine applicator with the Spraycox double nozzle spray cabinet.

By applying Coccivac-B vaccine on an angle from two sides, the new double nozzle system achieves a more uniform application across a box of chicks compared to the single nozzle, which applies from directly above.

Results encouraged the next trials to be free of in-feed medication

The two trial flocks showed a definite improvement. Gaining confidence from the success of the first two trials, Ambrose has completed two more successive flocks on his farm without any in-feed medication. The first flock was grown in one house, while the other house used traditional in-feed anticoccidials and antibiotics. At the end of the day, the antibiotic-free flock finished at 0.03 kg ahead of the traditional flock and half a day earlier, with similar mortality in both flocks. The second ABF flock was also paired with a traditional flock and finished a full day ahead at 0.01kg (0.022046 lb) heavier than the traditional flock. Mortality after the first week remained normal in the ABF flock in spite of high early chick mortality. The flock even experienced unusually severe weather during the growout period. Severe weather can often trigger necrotic enteritis outbreaks. The flocks were grown at the same density, but the ABF flocks had the advantage of the specially formulated feed.

According to Ambrose, "Incorporating passive antibody from the new experimental vaccine with Coccivac-B vaccine provides a promising solution for drug-reduced production in broiler chickens." In fact, Sunrise Farms has been so encouraged by the results on Ambrose's farm that they have challenged Ambrose to train Sunrise Farm managers and service personnel in the management techniques necessary to make drug-reduced broiler production economically feasible. Enhanced management, specially formulated feeds and a passive antibody from the new experimental vaccine may enable producers to produce economical antibiotic- free broilers in the near future.

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