IN a project funded by the U.S. Poultry & Egg Assn. and its foundation, Drs. Robert B. Beckstead and Larry R. McDougald of the University of Georgia department of poultry science used molecular techniques to track outbreaks of blackhead disease in poultry, correlate these outbreaks with specific isolates of Histomonas meleagridis and identify genes associated with the virulence of specific isolates.
Additionally, the project tested whether a vaccination approach could be used to protect turkeys from this disease.
Isolates from outbreaks in turkeys, broiler breeder chickens, layer chickens and bobwhite quail were tested for virulence and were categorized by molecular markers, the researchers said.
The objectives of the research were to:
1. Survey H. meleagridis field isolates from turkeys, broiler breeder pullets and wild birds for variations in virulence and correlate virulence to molecular markers that classify H. meleagridis stains;
2. Investigate the epidemiology of field isolates obtained from H. meleagridis outbreaks using molecular markers and identify potential disease reservoirs and modes of transport of H. meleagridis between farms;
3. Establish and validate a molecular diagnostic test for H. meleagridis, and
4. Establish a vaccination protocol to stimulate protective immunity in turkeys.
Beckstead and McDougald said their data confirm that there are multiple disease reservoirs and that most outbreaks of blackhead arise from distinct isolates of H. meleagridis. Isolates varied considerably in virulence, sensitivity to nitarsone and expression of virulence genes.
Variations in mortality and morbidity in outbreaks in the field were a result of the virulence of the associated isolate, particularly in chickens, the researchers said. Based on their data, they noted that litter from breeder or layer pullets is likely to contain cecal worm (Heterakis galllinarum) eggs — the known vector for H. meleagridis — and is the most likely source of infection in turkeys.
Noting that this confirms earlier work, Beckstead and McDougald suggested that their study emphasizes the increasing infection pressure resulting from overlapping areas of broiler breeder chicken farms and turkey farms.
One strain of H. meleagridis isolated from layer pullets resulted in 17% mortality in chickens in the laboratory, emphasizing the potential of this parasite to devastate chicken flocks as well as turkeys, they said.
Beckstead and McDougald noted that they designed a new molecular-based method to diagnosis H. meleagridis in samples obtained from tissue. This polymerase chain reaction-based method is specific to H. meleagridis and allows for quick diagnosis without costly DNA sequencing.
Vaccination approaches using attenuated live and killed preparations tested by the group failed to produce adequate, timely blackhead protection in turkeys, Beckstead and McDougald reported, noting that a delay in the onset of the disease in birds given live attenuated H. meleagridis was observed, but complete protection was never attained.
Beckstead and McDougald concluded that a significant part of the biology of H. meleagridis and its interaction with chickens and turkeys is poorly understood. Based on their data, there are many local reservoirs of infection in the environment, increasing the difficulty in preventing blackhead outbreaks.
More research is needed to identify insects or other mechanical carriers responsible for the survival and spread of blackhead, the researchers said. They noted that caution should be used in spreading litter from infected farms near other poultry operations.
At the recent Mid-Atlantic Nutrition Conference, James H. Lewis and Isa Ehr of Iowa State University and Michael E. Persia of Virginia Tech University presented a research abstract on producing eggs that have increased omega-3 fatty acid content by including flaxseed oil in the diets of laying hens.
Lewis et al. said their objective was to compare the effectiveness of milled flaxseed and extracted flaxseed oil as sources of omega-3 fatty acids to increase egg yolk concentrations.
In total, they used 132 first-cycle W-36 Hy-Line laying hens in four replicate groups of three hens for each of 11 dietary treatments. A control diet was formulated without milled flaxseed or extracted flaxseed oil, and 10 diets were formulated to contain 0.5%, 1.0%, 2.0%, 3.0% or 5.0% flaxseed oil generated by the addition of either milled flaxseed or extracted flaxseed oil.
The hens were fed experimental diets for eight weeks, and five eggs per experimental group were collected and pooled during weeks 4, 6 and 8 for fatty acid analysis, Lewis et al. said. Hen feed intake, egg production, egg weight, egg mass and feed efficiency were calculated for the eight-week period.
The regression analysis of flaxseed oil versus egg yolk omega-3 fatty acid content resulted in highly significant linear equations for both extracted flaxseed oil (y = 1.8051x + 1.4253; R-square = 0.98) and milled flaxseed (y = 0.8826x + 1.7034; R-square = 0.90), the researchers reported.
When comparing the slopes of the two equations, Lewis et al. said it is clear that feeding extracted flaxseed oil resulted in greater transfer of omega-3 fatty acids to the egg yolk compared to milled flaxseed. These data suggest that the extraction process somehow increases the transfer of fatty acids from the diet into the body and eventually into the egg yolk, they added.
The experiment suggests that flaxseed oil is more efficient at increasing egg yolk omega-3 fatty acid concentrations compared to equal amounts of oil from milled flaxseed and is a valuable source of omega-3 fatty acids for egg producers to consider, Lewis et al. concluded.
Common chicken traits
The chickens of today may not much resemble the chickens living just a few-hundred years ago.
Ancient DNA adds a twist to the story of how barnyard chickens came to be, according to a study published April 21 in the journal Proceedings of the National Academy of Sciences.
Analyzing DNA from the bones of chickens that lived in Europe between 200 and 2,300 years ago, researchers reported that just a few-hundred years ago, domesticated chickens may have looked far different from today's chickens.
The results suggest that some of the traits associated with modern domesticated chickens — such as their yellowish skin — became widespread much more recently than previously thought.
"It's a blink of an eye, from an evolutionary perspective," said co-author Greger Larson at Durham University in the U.K.
The study is part of a larger field of research that aims to understand when, where and how humans turned wild plants and animals into the crops, pets and livestock known today.
Chickens are descended from a wild bird called the red junglefowl that people started raising roughly 4,000-5,000 years ago in South Asia. To pinpoint the genetic changes that transformed this shy, wild bird into modern chickens, researchers analyzed DNA from the skeletal remains of 81 chickens retrieved from a dozen archeological sites across Europe dating from 200 to 2,300 years ago.
The researchers focused on two genes known to differ between domesticated chickens and their wild counterparts: a gene associated with yellow skin color called BCDO2 and a gene involved in thyroid hormone production called TSHR.
When the team compared the ancient genetic sequences to the DNA of modern chickens, only one of the ancient chickens had the yellow skin so common in chickens today. Similarly, less than half of the ancient chickens had the version of the TSHR gene that is found worldwide in modern chickens.
The results suggest that these traits became widespread only within the last 500 years — thousands of years after the first barnyard chickens came to be.
"Just because a plant or animal trait is common today doesn't mean that it was bred into them from the beginning," Larson said.
"It demonstrates that the pets and livestock we know today — dogs, chickens, horses, cows — are probably radically different from the ones our great-great-grandparents knew," he added. "They are subjected to the whim of human fancy and control, (so) radical change in the way they look can be achieved in very few generations."
Other authors of the study include Linus Flink, Richard Allen and Ross Barnett of Durham University; Helena Malmstrom, Jonas Eriksson and Leif Andersson of Uppsala University in Sweden; Joris Peters of Ludwig Maximilian University in Munich, Germany, and Keith Dobney of the University of Aberdeen in Scotland.
Their study was part of a collection of articles in a special edition of Proceedings of the National Academy of Sciences devoted to domestication. This study and others featured in the special issue stemmed from a meeting that took place in 2011 at the National Evolutionary Synthesis Center in Durham, N.C.
More information about the meeting — titled "Domestication As an Evolutionary Phenomenon: Expanding the Synthesis" — can be found at http://domestication.groupsite.com/main/summary.