Sometimes the best way to identify disease problems is to use sentinel birds along with other diagnostic tools, but the specific-pathogen-free (SPF) birds used for this purpose aren’t always readily available.

In these cases, broilers can be used instead if they’re hatched by the broiler company and are raised in isolation.

SPF birds are not only raised in isolation, they are also guaranteed to be pathogen-free, so any viruses or diseases isolated from them come from the field, Tim Cummings, DVM, senior technical services veterinarian, Zoetis, told Poultry Health Today.

Cummings cited a case with a company experiencing respiratory problems in its flocks. Diagnostics were being performed and they also wanted to include sentinel birds, but SPF birds weren’t available at that time.

Instead, they used the broiler company’s own day-old chicks that were hatched and placed in isolation to minimize exposure to any disease.

At 4 weeks of age, 10 each of the isolation-raised chickens were put in pens in 20 chicken houses, each on a different farm. Those birds were used as the sentinel birds. A week after placement on farms, the birds were collected. Samples were taken from tracheas, lungs, kidneys and cecal tonsils and were submitted for virus isolation.

Cummings said the viruses isolated on all 20 farms were vaccine viruses, which indicated there weren’t any variant bronchitis viruses in the field causing problems. Since this effort was a follow-up to vaccination changes made by the broiler company, the sentinel birds confirmed that no new bronchitis vaccines were needed.

The veterinarian cautioned that while producers can use their own broilers versus SPF birds when trying to isolate diseases from broilers, there’s no guarantee they’re pathogen-free even when raised in isolation.

He also noted that, “when we put these broilers in the chicken houses, they’d never been exposed to coccidia, so some of them had rip-roaring cases of coccidiosis when we sampled them.”

New research by Callie McQuain, DVM, veterinarian and grad student at the University of Georgia, substantiates anecdotal field experience indicating that Eimeria maxima is the type of coccidia that most interacts with Clostridium perfringens and leads to necrotic enteritis (NE).

New research by Callie McQuain, DVM, veterinarian and grad student at the University of Georgia, substantiates anecdotal field experience indicating that Eimeria maxima is the type of coccidia that most interacts with Clostridium perfringens and leads to necrotic enteritis (NE).

The reason why C. perfringens grows so readily in these flocks is because of the type of damage E. maxima causes to intestinal mucosa, she told Poultry Health Today.

Common industry knowledge has been that E. maxima is the No. 1 coccidial species that leads to NE; McQuain’s research now establishes that as fact, she said.

Clostridium is part of the gut flora. Together with the coccidial damage, it creates a perfect storm that allows it to grow exponentially and results in NE, McQuain noted.

As poultry producers either reduce or eliminate antibiotics, it’s hard to stop NE from becoming severe. The emphasis now is on preventing the coccidia from damaging the gut, she said

McQuain recommends adding citric acid or some kind of acidity to the water system, which decreases the pH so Clostridium will not grow as fast. It is also important to quickly collect birds that have succumbed to NE to minimize the presence of Clostridium in the poultry house.

Research into the immune response of chickens could help lead to strategies that enable chickens to resist infectious bronchitis (IB), Rodrigo Gallardo, DVM, PhD, professor, University of California – Davis, told Poultry Health Today.

Research into the immune response of chickens could help lead to strategies that enable chickens to resist infectious bronchitis (IB), Rodrigo Gallardo, DVM, PhD, professor, University of California – Davis, told Poultry Health Today.

Investigators at the university have focused on the link between the innate and the adaptive immune response of chickens and have identified components that affect resistance.

The innate immune system consists of cells and proteins that are always present and ready to mobilize and fight microbes, while the adaptive immune response system is called into action against pathogens able to evade or overcome innate immune defenses, Gallardo explained.

The investigators are now applying what they’ve learned about resistance to the development of IB-control strategies, which might ultimately include different ways of vaccinating with the same products now available or the addition of different vaccine adjuvants, he said.

Although the research is currently focused on IB, it’s possible the results of the research might also lead to methods of enabling chickens to resist other types of respiratory infections in addition to IB, Gallardo noted.

 

Necrotic enteritis (NE) is not only a big problem in flocks raised without antibiotics, there’s a wide variation in how it presents itself, Steve Davis, DVM, president of Colorado Quality Research, told Poultry Health Today.

Necrotic enteritis (NE) is not only a big problem in flocks raised without antibiotics, there’s a wide variation in how it presents itself, Steve Davis, DVM, president of Colorado Quality Research, told Poultry Health Today.

In birds raised without antibiotics, NE is much more severe in some flocks than in others. The age of onset also varies widely, Davis continued.

NE used to be considered age specific, almost always showing up between 14 and 24 days of age. Now, it appears on some farms before 7 days of age, but on other farms, it doesn’t show up until 35 days of age or older, he said.

“Where a company or complex is seeing a specific timing of this syndrome, it seems to be fairly consistent within that complex. But there’s no consistency from one company to another,” Davis said.

Management factors come into play, he continued. Humidity, feeding programs, feed changes and feed-ingredient quality all play a role in what Davis considers to be a disease syndrome.

He also reported seeing more NE in complexes using non-ionophore anticoccidials compared to ionophores.

Companies that are still using conventional methods, particularly feed-grade antibiotics and ionophores, don’t have NE, he said. Ionophores are very effective against coccidiosis, and good coccidiosis control can help prevent Clostridium perfringens, a cause of NE.

“Our old methods that we’ve had for years still work, but as the industry has chosen — or the consumers are pushing our industry — to move away from those methods, we’re getting more and more NE,” Davis said.

Anticoccidial-rotation programs are definitely an important way to help control coccidiosis and, in turn, prevent NE in flocks raised without antibiotics. Although there’s not any one rotation program that works for everyone, bioshuttle programs — a combination of vaccines and anticoccidials — seem to be working the best, he noted.

Daral Jackwood, PhD, a professor at Ohio State University, is best known in the US poultry industry as the go-to expert on infectious bursal disease (IBD). In an interview with Poultry Health Today, he explained the complexity of managing this difficult and costly disease.

Daral Jackwood, PhD, a professor at Ohio State University, is best known in the global poultry industry as the go-to expert on infectious bursal disease (IBD). In a far-ranging interview with Poultry Health Today, he talked about how IBD variants emerge, vaccine selection, viral shedding and the spread of the virus, the merits of vaccine rotation and special considerations for antibiotic-free production schemes.

Watch the full interview

Part 1: Why the focus on IBD?

Jackwood said he started his graduate career studying bacterial diseases of poultry. It was clear to him early on that IBD viruses led to immune suppression that exacerbated other diseases. “I got interested in what causes immune suppression in poultry… and I just carried that over into my career,” he said.

Part 2: Understanding IBD variants

In the 1980s, it was discovered that genetic variants of the IBD virus weren’t controlled with current vaccines. That became the definition of a variant virus.

Although some vaccines were made for variant IBD viruses, more new variants were springing up and it became clear the industry wasn’t going to win the battle with conventional vaccines, he said.

The very virulent IBD viruses also came onto the scene in the 1980s, emerging first in Europe and eventually around the world.

Jackwood notes that the terms used to describe IBD viruses can be very confusing but said there are three major designations. There are classic IBD viruses — the ones first isolated in Gumboro, Delaware in the 1960s. The second group are the antigenic variants isolated in Delaware in the 1980s. The third group are the very virulent IBD virus strains first seen in Europe.

However, there are a range of viruses within each of those three groups. “So, it’s not black and white. It’s much more gray than that,” he said.

Part 3: IBD: Matching vaccine to variants

“With vaccine programs, the key thing is getting the antigenic strain of your vaccine to match with the antigenic strain of the field virus that’s causing the disease problem,” Jackwood said.

The antigenic differences are critical. If the vaccine strain doesn’t match the field virus, the vaccine will not protect birds.

Part 4: Planning your IBD vaccination program

Protecting very young birds is a must. “That first 2 to 3 weeks of life are critical, because that’s when the virus is infecting the B-lymphocytes and causing the immune suppression,” Jackwood explained.

To keep young birds from becoming infected, the industry vaccinates breeder flocks to provide maternal antibodies to their broiler progeny.

However, maternal antibodies wane, so it’s important to also vaccinate broilers to help protect them, Jackwood said.

Previously, live attenuated vaccines were used, but timing of vaccination could be problematic due to maternal antibodies. The advent of herpesvirus (HVT) vaccines that express the bursal disease virus VP2 gene have changed everything. They can be given while maternal antibodies are high, and provide good cross-protection as the birds get older, he said.

Part 5: Viral shedding and the spread of IBD virus

IBD viruses are transmitted via the fecal-oral route. Eventually, birds are going to shed the virus in feces. In a study Jackwood previously conducted, he said he found the virus is only shed for a short period of time, but it’s shed in very large numbers.

Identification of variant infectious bronchitis viruses (IBVs) has improved with the development of a real-time PCR (qPCR) test that can distinguish the type of virus and determine if it’s vaccine- or field-related.