Ensuring strong immunity key to successful NAE broiler production
Producers raising broilers with no or fewer antibiotics need to pay more attention to diseases that can compromise flock immunity and make birds more susceptible to primary and secondary
infections, according to poultry specialists speaking at an industry roundtable.
“If we can prevent birds from becoming immune-suppressed and getting secondary bacterial infections, we may be able to get away with using fewer antibiotics,” Daral Jackwood, PhD, of Ohio State University, said at the roundtable, “Optimizing immunity in ‘no antibiotics ever’ and ‘reduced use’ broiler flocks.”
The panelists focused on three viruses that by themselves lead to losses but also predispose flocks to a variety of other diseases that can impair performance and producer profits: infectious bursal disease (IBD), reovirus and Marek’s disease.
“Control of these viruses is…critical” in flocks raised in “no antibiotics ever” (NAE) production systems, said Guillermo Zavala, DVM, Avian Health International, LLC.
Start with breeders
John Smith, DVM, Alectryon, LLC, said control of immunosuppressive diseases like IBD or reovirus, at least under US conditions, requires hyper-immunization of hens using strains as close as possible to resident challenge strains.
Zavala noted that, “We don’t always protect birds…100% the way we’d like to, but for the most part, the vaccines we have for use in the field are good tools.”
When roundtable moderator Jean Sander, DVM, Zoetis, asked if vaccinating breeders against IBD will ensure broilers have access to maternal antibodies during their first 14 days of life, Jackwood said, “You need to get the titers of antibodies [to IBD] very high so breeders pass those antibodies on to broiler chicks through the yolk.”
Kalen Cookson, DVM, Zoetis, advised priming breeder pullets with IBD vaccines. Until the advent of recombinant vaccines, it was virtually standard practice to use an intermediate vaccine at about 18 days of age, usually followed by one live intermediate-plus or strong vaccine at around 5 to 6 weeks of age.
“Historically, that program worked very well for priming the immune system so pullets could respond well to the killed vaccines they got later on.”
Recombinant IBD vaccines are valuable and have a place, Cookson continued, but may actually reduce the circulating field challenge. That’s all the more reason to keep a strong, live vaccine in the program, he said.
Zavala said, “I don’t typically see recombinant vaccines used as a sole vaccine prior to the use of killed vaccines…Wherever producers have attempted to use only recombinant vaccines followed by killed vaccines, they typically go back to the more traditional programs.”
Bursal-derived IBD vaccines ‘superior’
Smith and Jackwood said killed bursal-derived IBD vaccines provide advantages. “The amount of high-quality antigen you get with bursal-derived vaccines is much higher than you can get with egg- or cell-cultured vaccines. That’s why the bursal-derived vaccines work better,” Jackwood noted.
Mark Burleson, DVM, of Wayne Farms, strongly advised auditing vaccination crews and monitoring antibody titers to ensure all breeders are receiving IBD killed vaccines. Sometimes companies establish a strong vaccination program and assume it’s being administered correctly, but “I’ve seen first-hand that they don’t always follow up.”
Elizabeth Dale, DVM, of Pilgrim’s, also believes in live-priming followed by inactivated vaccines for breeders, but said “…we wrestle with finding appropriate commercial [killed] vaccines that have homologous strains that match the field challenge,” which creates the need for the use of autogenous vaccines.
Dale and Smith expressed frustration with the complicated and lengthy regulatory process involved. With autogenous vaccines, “You’re a year out before you see protection in your broilers. Too often by that time, the field challenge may have changed,” Dale said.
Jackwood, however, predicted that autogenous vaccines may be on their way out. New technology is fostering development of genetically engineered vaccines made up of virus-like particles or combinations of proteins that match field viruses, and they promise to be “very, very effective.”
IBD vaccination of broilers
Several panelists advocated IBD vaccination of broilers as well as breeders. When broilers are about 3 weeks of age, Jackwood said, maternal antibodies are low enough for birds to become infected with IBD field virus unless they have active immunity. “Vaccinating broilers before those maternal antibodies drop too low is really the key,” but the timing of vaccination can be tricky, he indicated.
Jackwood advised vaccinating broilers when about 70% to 75% of the flock have titers low enough for vaccine “take.” “If it’s less than that, you’re just not going to get a really good immune response from your vaccine.”
Sander pointed out that although challenge studies are ideal for demonstrating IBD vaccine efficacy, they are impractical for most producers. She asked what can be done to ensure an IBD vaccination program is working.
Several panelists said they depend on bursal surveys. Smith examines bursas during routine postmortems and compares them to standards for that age and bird. He also relies on periodic bursal surveys; selected flocks are sampled at least two and sometimes three times, usually between 2 to 4 weeks of age. Bursas are measured or a bursa-to-bodyweight ratio is determined.
“More valuable is histopathology,” Smith said. An experienced pathologist can very accurately predict which bursas have active infection and are good candidates for viral detection, which ultimately leads to the IBD strains used for autogenous vaccines.
Jackwood added, “Here in the US, the IBD viruses infecting our flocks are causing subclinical disease — so there aren’t any clinical signs. The only way you’ll know you have IBD is by examining the bursas to see how large they are.”
Dale prefers to look at overall performance before initiating a bursal survey. “If performance starts slipping, we’re having late mortality or increased condemnations at the plant due to opportunistic, secondary-type infections and I see colibacillosis or a secondary-type respiratory infection, I look for underlying bursal issues and conduct a bursal survey.”
Panelists said a lot less is known about reovirus and its effect on immunity compared to IBD.
Holy Sellers, PhD, University of Georgia, said, “We don’t know the extent of immunosuppression that various reoviruses cause.” Some cause incredible lymphocyte depletion in the bursa, while others cause viral arthritis and tenosynovitis, yet the bursas look okay.
Cookson said reovirus is more challenging to deal with compared to IBD because it can be vertically transmitted.
Smith and Sellers agreed that commercial reovirus vaccines have been a success story.
The strategy of live-prime/boost provided good protection, Sellers said, but “What’s different now is that we are missing the homologous, live-vaccine component (to help protect against and prime for variant strains).”
Reovirus vaccination programs for breeders vary widely with various combinations of live, killed and autogenous vaccines, Sellers continued. “What you’re trying to do is extend the duration of immunity so that you can prevent vertical transmission…You also want to be sure that chicks have adequate levels of maternal-derived antibodies to protect during the first week or so when they are most susceptible.”
Selection of appropriate isolates for an autogenous vaccine can be very complicated and is getting more so. “What I’m seeing is a change in the genetic and antigenic profile of the viruses. It’s shifting pretty rapidly, and it’s hard to predict or to make recommendations for what you need to use. It’s really a best guess…and then we come back to the race against time,” she said.
Monitoring for reovirus
Several panelists recommended serology to monitor reovirus status. “If you follow your [breeder] flocks serologically, follow their performance and the health status of your progeny birds and you don’t have a significant frequency of reovirus-like problems in the field, I think for the most part that gives you a good assessment,” Zavala said.
Serology in broilers is another good barometer of circulating reovirus, he said. “It doesn’t reflect things 100%, but when you have a problem, seroconversion tends to be a very magnified version of what you normally have. It’s very quickly clear.”
Burleson said, “The good thing about reovirus diagnostics is that it’s pretty classic. You know if your vaccination program is working or not because you typically have lesions…the tenosynovitis is usually obvious.”
Sellers agreed that reovirus can often be diagnosed in the field “if you start looking at the right ages — between about 2 and 4 weeks of age in your broilers.” However, she’s found recently this is also changing.
“I’ve gotten some isolates from complexes where there are no obvious gross lesions or tenosynovitis at the time of active infection, but we’ve seen weight suppression and then tendon ruptures at older ages. It’s getting harder to find the correct samples to take in broilers because now we’re seeing more of these variants with much more subtle lesions during active infection. I don’t know that we have looked explicitly at immunosuppression; we’re not necessarily seeing secondary infections,” she said.
Marek’s virus, Zavala explained, replicates actively in birds that aren’t properly protected. First, B cells are affected and their ability to produce antibodies. After a few rounds of replication, the virus infects T cells and impairs their function. “If you affect B cells and T cells, you’re effectively damaging almost the entire ability of the immune system,” he said.
Recent research, he continued, confirms something that’s been suspected for a long time: The dose of Marek’s vaccine that will protect against tumor expression may not be enough to protect the immune system. “In other words, when you fractionate doses of Marek’s disease vaccine [to save money], you may be avoiding tumors at the plant, but you may not be protecting adequately against immunosuppression.”
Pilgrim’s Dale said most of her experience with Marek’s disease vaccines is with the recombinants. “As Dr. Zavala noted, I’d advise making sure the full dose is used. In addition, there are times in higher challenge regions when SB1 needs to be added to the herpesvirus of turkey. That seems to give good overall coverage.”
Impact of RWA trend
Dale said the push toward antibiotic-free production has “really prompted us to be more meticulous in every aspect of the entire process…
“In our case, it’s improved our hatcheries greatly. It’s been surprising that a couple of complexes raising birds without antibiotics (RWA) are top-performing in their production class. We’ve seen the same thing in our organic complex. It’s beating our conventional birds of the same size. It has a lot to do with the management that’s put into place when you are raising birds without antibiotics,” she said.
Zavala, who has worked with a number of poultry companies in the US and many other markets, said one of the first things realized is that transitioning to antibiotic-free production is not like turning a switch to get instant results. It’s a process that requires sometimes years of hard work and standardization of procedures.
“Withdrawing antibiotics has forced the industry to be much more stringent about their process and requirements in general. You can’t operate with floor eggs the way you used to. You cannot overlook hygienic issues in nests the way you used to,” he said.
Wayne Farms’ Burleson noted, “Remember that it starts at the breeder farm.” It requires a lot of attention to detail. Standard operating procedures should be aimed at ensuring good chick quality. If you put out a good chick, it already has a good head start, he said.
Smith said, “That’s all true. There’s no magic bullet. It’s elbow grease and hard work and attention to detail. It’s ventilation. It’s litter management. It’s lighting programs and water sanitation. Just the nuts and bolts of raising a healthy chicken, including a high-quality diet…We know that stress is immunosuppressive, so you have to do everything you can to reduce stress for the bird,” he said.
Dale said, “Where we have been successful thus far can be attributed to starting the process in advance of making the transition, with attention to those things Dr. Smith mentioned are necessary for raising a healthy chicken…If you’re transitioning to antibiotic-free production, start early and make the investment on the front end in your hatcheries. Make sure all other aspects of management are in good order. If you do that well in advance, it should be a smoother transition.”