The ELISA test and the enigma of the single tall bar in the chart

Marcin Śmiałek, Joanna Kowalczyk, Bartłomiej Tykałowski, Andrzej Koncicki 

Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland

ELISA tests, and serological assays in general, are highly practical tools for rapid and relatively low-cost diagnosis of infectious diseases and epidemiological monitoring of poultry flocks (also having wider application). What is the one tall bar in an ELISA test result chart?

Appraising the data presented above, it is impossible not to form the impression that the result climbs rapidly as we read rightwards and then suddenly “hits a wall” which it cannot break through. This impression could not be falser, because the result actually “hits” the upper limit of sensitivity of the test. Quite understandably, this may seem odd, given that the average titer fluctuates in a 6,700–6,800 range and the histogram clearly shows the bars not rising at all for 8 out of 18 groups. How may this be explained? It transpires from more detailed analysis of the results shown that the OD of the majority of the tested samples does not exceed a maximum value of 3 (this may not be higher because of the intensity of stain of the diluent in the ELISA plate wells). However, the issue of the high antibody titer value of the sample still remains. In the specific case of this test, the OD of the positive control was also very high (1,082–1,149). If the OD of the tested sample reaches the maximum value and the positive control OD rises at the same time, then the S/P ratio (sample OD / positive control OD) falls, and as a consequence the antibody titer also falls (this being calculated on the basis of the S/P parameter). A paradoxical situation then arises, because mathematically, the average titer of 6,700–6,800, as one perhaps undeserving of particular attention in the normal course of things, transpires to be an out-of-range result in this test. In such cases, the interpretation of the test results must be appropriate and the titer must be acknowledged to be a purely mathematically derived numerical value which may not represent the situation in the flock regarding the specific epidemiological risk tested for.

This summarises an article published in Polski Drobiarstwo [Polish Poultry Farming], issue 1, 2021. The full article may be found at

Is vaccinating turkeys against Marek’s disease justified?

Marcin Śmiałek DVSc1, Joanna Kowalczyk DVM1, Adam Śmiałek DVM2, Prof. Andrzej Koncicki1

“Marek’s Disease (MD) is a viral disease of foraging poultry affecting chickens, Japanese quail and presently also turkeys” was the simple lead-in to the section dealing with the issue of Marek’s Disease in poultry flocks authored by Professor Elżbieta Samorek Salamonowicz in the compendium edited by the late Professor Michał Mazurkiewicz entitled “Choroby Drobiu [Poultry Diseases]”. Despite the simplicity of that sentence, we have come to understand that many different opinions are current with regard to this particular point – “presently also turkeys”. Live naturally apathogenic (HVT) or attenuated (Rispens) vaccines are used in the specific prophylaxis of MD, given to birds on their first day of life via subcutaneous or intramuscular injections.

Reviewing the scientific literature and publications in popular science, it was difficult to find works written with a focus on purely practical matters and addressing the question of whether to vaccinate or not.. In the course of the review, we nevertheless reached the conclusion that the answer is affirmative; however, it depends upon several factors, chief among which are the particular vaccine which is intended to be administered and how real the risk is of disease in the particular turkey flock. The principal findings collated from individual data presented in a review article of July 2017 may be summarised as follows:

  1. HVT. Assuming the main source of Marek’s Disease Virus (MDV) infection in turkeys is chickens, the HVT vaccine should only be expected to protect birds against the first serotype with relatively low virulence (m/vMDV), and will be no match for the viruses which are dominant in Poland with higher virulence (vv/vv+MDV).
  2. Rispens. The application of this strain in the specific prophylaxis of MD broadens the range of protection to include higher virulence MDV. Unfortunately, this vaccine may transpire to be ineffective in the light of the emergence of oncogenic “turkey” strains of MDV in a given region. The capacity of the Rispens strain to replicate effectively in lymphatic system cells has not been elucidated to date, and neither, as a corollary, has its potential to have consequences collectively described as immunosuppressive.
  3. Rispens + HVT. The application of this vaccine gives the best effects in terms of imparting of protection against infection with high-virulence MDV (vv/vv+MDV). Its main drawback may once again turn out to be the potential to have immunosuppressive action.

This summarises an article published in Polski Drobiarstwo [Polish Poultry Farming], issue 7, 2017. The full article may be found at

1Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland
2Veterinary Surgery, Leszczynek 11A, 99-300 Kutno, Poland

Current knowledge on TRT epidemiology, diagnosis, and immunoprophylaxis

Marcin Śmiałek DVSc1, Joanna Welenc DVM1, Prof. Andrzej Koncicki1

Avian metapneumoviruses (aMPV) are highly contagious disease agents causing upper respiratory tract infections predominantly in turkeys, but also in chickens. The disease caused by aMPV has different courses in turkeys and chickens and because of this is designated turkey rhinotracheitis (TRT) in flocks of turkeys, with infectious inflammation of the nares and windpipe as its symptoms, but in flocks of chickens it is termed swollen head syndrome (SHS).

Metapneumovirus infections inflict significant losses on the poultry industry mainly as consequences of poorer body weight gains, directly caused deaths, declines in laying performance, and immunosuppression making birds more vulnerable to secondary infections.

Metapneumoviruses were first identified in the late 1970s in Southern Africa but from that time onwards they have come to be distributed across the whole world apart from Australia and Canada.

One of the most serious consequences of bird infections with aMPV is the risk of immunosuppression, which arises principally because of damage to the natural defensive barrier that the mucous membranes of the respiratory tract provide. This immunosuppression renders birds more susceptible to secondary infections, which are most frequently bacterial but may also be of another nature, and such infections in turn lead to a more severe clinical disease course and heavier production losses.

The similarity of the clinical course of TRT to those of other diseases demands exhaustive laboratory diagnostic testing for definitive confirmation of this disease. For this, ELISAs and PCR techniques are extremely useful tools.

Two main courses of action can currently be distinguished for limiting losses due to TRT: (1) flock biosecurity and (2) specific immunoprophylaxis. Two types of vaccine are currently used in the immunoprophylaxis of TRT, these being attenuated live vaccines based on A or B subtypes and inactivated vaccines. Despite the widespread vaccination of poultry, cases of wild-type strains of aMPV defeating post-vaccination immunity are frequently observed.

A more detailed treatment of these issues may be found through the link to the articles which provided the basis for this very brief report.

This summarises articles published in Polski Drobiarstwo [Polish Poultry Farming], issues 3, 4, and 5, 2018. The full articles may be found at

1Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland

The significance of Aviadenoviruses in turkey pathology

Marcin Śmiałek DVSc1,2, Michał Gesek DVSc3, Bartłomiej Tykałowski DVSc 1, Joanna Welenc DVM1, Prof. Koncicki Andrzej1

Adenovirus infections are highly prevalent among birds, but nevertheless it is worth emphasising at the outset that their significance in poultry pathology is a divisive question and one where several controversies rage. These viruses have been categorised into the three genera of Avi-, At-, and Siadenovirus. In the Aviadenovirus genus, there have so far been 14 species of virus identified which infect chickens, turkeys, ducks, pigeons, geese, psittacines, and Hawks. Three species of turkey aviadenovirus (TAdV) have been identified thus far and they are B, C, and D. Two serotypes have been differentiated in the TAv B species, TAdV-1 and -2, and TAdv-4 and -5 are the representatives respectively of species C and D. Serotype TAdV-3 in the Siadenovirus genus is the virus causing haemorrhagic enteritis in turkeys.

Aviadenoviruses may be isolated from both healthy and diseased birds and are typically not capable of inducing a disease state without other contributive factors. These viruses are extremely often isolated from birds which have previously recovered from immunosuppressive infections. Pathogens of this kind are stated as the primary cause of such broiler chicken diseases as inclusion body hepatitis (IBH), hydropericardium syndrome (HPS), gizzard erosion (GE), and tenosynovitis. Aviadenoviruses are also involved in respiratory tract diseases and exhibit immunosuppressive properties causing lower effectiveness of prophylactic vaccinations.

These viruses are also highly prevalent in the turkey population. They have frequently been isolated from samples in cases in which the disease course is marked by respiratory symptoms, diarrhoea and gastrointestinal tract symptoms and declines in laying performance; however, the majority of attempts to recreate the clinical course of the disease experimentally using “turkey” isolates have not yielded effects.

To date, only cases of IBH and inclusion body tracheitis in turkeys which had clinical disease courses correlating strongly with aviadenovirus infection have been more thoroughly identified and described. Rare cases of GE in turkeys have also been described; however, the majority of these were identified with the action of intoxicants. On the other hand, Minta and Koncicki described a clinical case of GE in 2–3-week-old slaughter turkeys in 1996 where agar gel precipitin test results suggested an adenovirus as the aetiological agent of the disease.

The authors’ observations lead to the conclusion that the significance of Aviadenoviruses in turkey pathology is rising, while further research is still needed to establish the infection route and the role of the viruses in the development of the diseases in the cases described.

This summarises an article published in Polski Drobiarstwo [Polish Poultry Farming], issue 2, 2019. The full article may be found at

1Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland
2SLW BIOLAB s.c., Ostróda, Poland
3Chair of Pathological Anatomy, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland


Pendulous crop

Marcin Śmiałek, Andrzej Koncicki

Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland

A well-functioning gastrointestinal tract providing a means of absorbing essential nutrients as required for rapid feed conversion is essential to avian health, which translates to profitability of production in large-scale poultry farming. There are many pathologies of the avian gastrointestinal tract, but the literature devotes little attention to cases of pendulous crop, which have been an inherent part of poultry production for many years.

The avian crop is a thin-walled bulge at the posterior part of the oesophagus which contains feed whenever the gizzard is full. Feed in the crop is not digested but is only moistened. When the stomach empties, the contents of the crop are transported further along the gastrointestinal tract by contractions of the muscles in the crop wall. There are three muscle layers which comprise the wall of the crop, which are enveloped in connective tissue. The crop is attached to its surrounding tissue by two muscles which stabilise it by having deep attachment points in the skin and are involved in emptying it. Contractions in the crop are stimulated by the vagus nerve.

The function of the crop may be defined as a store of feed, and it enables birds to “survive” the nocturnal period when they take no feed from their surroundings by being this store and thereby prolonging the time during which nutrition is supplied to the subsequent parts of the gastrointestinal tract. This action is also why differences in the extent to which the lumen of the crop is full of nutritive matter can be observed over the course of the day. In comparison with the morning, proportionally more feed is stored in the crop in the afternoon and evening. This proportional relationship was identified from confirmed higher feed intakes by domestic birds in the afternoon. It nevertheless transpires that the extent to which the crop is full has no bearing on how much feed is taken or on the bird’s satiety, as indicated by the extents to which the crop is full in birds differing greatly irrespective of the availability of feed. The main regulators of feed intake by birds are the physical form of the feedstuff, the activation of chemoreceptors which sense concentrations of glucose, amino acids and lipids and the activation of mechanoreceptors in various parts of the gastrointestinal tract (e.g. the extent of gizzard expansion), the protein and energy content in the portion of feed, the surrounding temperature, access to water, and the competence of the nervous and endocrine systems.

As the crop empties, it contracts at 60–90-second intervals, these contractions being dependent on the extent to which the stomach is full as well as on the type and consistency of the nutritive substance filling the crop. Soft contents are passed out of the crop more quickly than grain seeds, for example. However, the peristalsis of the crop can be disordered by certain avian pathologies, which can lead to impaired emptying of the residual excess of feed it contains.

Pendulous crop

A crop which is enlarged and greatly extended and which is hanging at the front of the bird’s chest is termed a “pendulous crop” (PC). In palpation through the skin, such a crop is soft and fluid can be felt moving inside (this can be compared to how a bag filled with water would feel if palpated), and this should be distinguished from a crop filled with ingested feed and functioning normally (when it has a consistent, dough-like feel).

The disorder of PC may be described as a pathology with complex aetiopathogenesis, and its causative factors are probably environmental, nutritional, and infection-related just as they are toxicity-related. Among the numerous causes, the majority of which have nevertheless not been scientifically proven, the most frequent reasons for the occurrence of pendulous crop are:

  1. Overfilling (particularly in chicks during their first days of rearing), which results in stretching of the elastic fibres of the connective tissue holding the muscle layers of the crop wall together. A consequence of the intensive stretching of these fibres may be their tearing, which leaves the crop unable to regain its original shape and dimensions. Alongside this, overfilling leads to damage to the integrity of the crop muscles, causing impairment of their capacity to contract and impairment of peristalsis. In such situations water or feed are not passed out of the crop completely, creating ideal conditions for the microorganisms such as bacteria, fungi, and protozoa which start secondary infections
  2. Excessive drinking, which most often is related to high summer temperatures in the poultry house and overheating of birds. In such situations the volume of water drunk may rise by 400%
  3. Excessive water intake occurs when birds are dehydrated, which most often happens when drinkers are defective or when transport of chicks from the hatchery to the premises where they will be reared takes too long and no provision is made for chicks to drink. Dehydration can also occur in the course of certain diseases such as necrotic enteritis or candidiasis
  4. Impurities in water which negatively affect its taste. In such situations birds drink copious and excessive amounts when the impurities are completely removed from the water or their concentrations fall to a low enough level not to affect its taste
  5. Excessive feed intake (following a period of feed deprivation, e.g. as chicks endure during transport of long duration)
  6. Systems restricting feed and water provision
  7. Physical or chemical irritation of the crop mucous membranes, which predisposes birds to secondary infections of those membranes and consequently puts them at risk of damage to the underlying muscles and connective tissue fibres
  8. Excessive admixture of dextrose in bird feed, which propagates Saccharomyces tellustris yeast and causes pronounced extension of the crop because of overproduction of gases
  9. Infection with the flagellate Trichomonas gallinae, which most often occurs when bird husbandry conditions are poor, and particularly when poor quality water is provided
  10. Damage to the innervation of the crop (by Marek’s disease or deficiency in group B vitamins, in particular B6 (pyridoxine))
  11. Poisoning with culinary salt, in the course of which the amount of water drunk increases dramatically

Besides the causes listed, a genetic predisposition in certain poultry breeds is often seen as the main underlying cause of PC; however, as yet no data confirm this theory.

The disease has a chronić course and few birds return to full health. Most often, only single individuals in a flock are affected by PC, but in extreme cases it may affect a reasonably high double-digit percentage of birds (8). Although birds may even live for 2 years with PC and broilers may attain slaughter age, they prevailingly demonstrate poorer body weight gains as a result of less effective utilisation of feed, despite retaining their appetites. This distinguishes the course of pendulous crop from impacted crop where the conditions frequently present the same signs. Mortality in flocks containing birds displaying typical clinical signs of PC may be as high as 50% of those birds. In these cases, the most common causes of death are ruptures of severely enlarged crops due to physical injuries, suffocation by heavily liquified and diluted crop contents, malnutrition as the effect of poorer utilisation of feed or hindrance of feed intake, and secondary infections.

The crop undergoes anatomical and pathological changes in birds with PC and in addition to its extreme enlargement and full content of semi-liquid matter with a foul odour, thinning and ulceration of its mucous membrane is frequently observed in necropsy. These lesions are extensive and disseminated necrotic foci. Besides these lesions, white spots resulting from secondary fungal infections are often noted in gross examination of the mucous membranes of the crop. In cases of PC caused by Trichomonas gallinae infection or infection with these flagellates where PC has not developed, isolated pyramidal lesions are observed and protozoa can be isolated from the mucous membrane.

Lesions are not noted during necropsy in other internal organs, with aspiration pneumonitis and the presence of undigested feed in the lumens of the trachea and bronchi only observed in extreme cases after suffocation by liquified and diluted crop contents.

Despite various therapeutic modalities for birds with PC described in the literature, therapy is not administered in large-scale poultry rearing operations. This is because of the costs associated with the treatment procedures and also because of frequent recurrence of PC despite therapy having been given. For this reason every care must be exercised to minimise the potential for PC in flock birds as much as possible. This prevention can be achieved principally by maintaining good conditions for rearing birds, ensuring the functionality and appropriate hygienic standards of drinking and feeding systems, providing feed and water of suitable quality, and keeping these free of impurities which affect their aroma and taste negatively. It is also necessary to monitor the amounts of feed consumed and water drunk by birds constantly, and on hot summer days in particular it is necessary to carry out surveillance of the regularity of birds’ eating and drinking.


Assigning defined daily/course doses for antimicrobials in turkeys to enable a cross-country quantification and comparison of antimicrobial use

This study presents a list of DDDturkey (Defined Daily Dose) and DCDturkey (Defined Course Doses) to allow for a species-specific, on farm quantification of AMU (antimicrobial usage) on European turkey farms. Assigning DDDturkey has shown the need for a unified European antimicrobial drug portfolio and harmonization of recommended doses across the SPCs of similar antimicrobial products authorized for use  in turkeys, at the least when treating identical diseases.

To read the full article, click here.

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Comparing various euthanasia devices and methods on 8 and 12-week-old turkey hens

On-farm euthanasia of poultry is a necessity for minimizing disease spread and removing sick or injured birds to maintain optimum animal welfare. There are numerous methods that are approved for euthanasia of poultry; however, all approved methods are not easily carried out on-farm or as effective as one another.

Therefore, the objective of this study was to compare several captive bolt devices (Turkey Euthanasia Device, Zephyr-EXL, Jarvis Stunner, Experimental Crossbow), mechanical cervical dislocation (Broomstick method [BRM] and Koechner Euthanasia Device [KED]), and manual cervical dislocation (MAN) methods on 8 and 12-week-old turkey hens. Each method was assessed for impact on loss of brain stem reflexes, euthanasia success, and torn skin.

To read the full article, click here.

Turkey Farming: How Intensive Breeding Is Transforming the Industry

For most Americans, Thanksgiving would not feel complete without a roast turkey on the dinner table. Legend has it that turkey was served at the First Thanksgiving in Plymouth Colony in 1621, and the Thanksgiving tradition of presenting turkeys to the U.S. president dates back to 1947. Eating turkey is considered an American tradition, but how turkeys become food is much less glamorous.

Turkeys available at supermarkets today are the result of intensive farming. Selective breeding and commercial farming techniques have altered the appearance and damaged the general quality of life for turkeys. Commercial turkeys have little in common with the wild turkeys of 1621 or even the domesticated turkeys of 1947. Today, millions of turkeys around the globe are bred, killed, and eaten every year.

What Is Turkey Farming?

Turkey farming is the practice of raising and slaughtering turkeys for meat. Domesticated turkeys are descended from Meleagris gallopavo, a subspecies of wild turkeys indigenous to parts of Mexico, Canada, and the United States. Turkeys were domesticated as early as 100 BCE in Mesoamerica and exported to Europe during the 16th century. But modern domesticated turkeys differ from wild turkeys in one big way: they are bred to gain weight quickly. And unlike chickens, domesticated turkeys are only farmed for meat and not for eggs.

The world’s top turkey producing country is the United States, followed by Brazil, Germany, France, and Italy. In the U.S., four states—Arkansas, Minnesota, Virginia, and Indiana—accounted for more than half of all turkeys slaughtered in 2019. The turkey industry itself is incredibly lucrative. The value of all turkeys produced in the U.S. during 2019 was $4.30 billion, and most turkeys were produced using intensive farming techniques. Only 3 percent of turkey meat revenue—$139 million—was generated by farms certified as organic.


5 Things I Learned About Turkey Farms

By Heather Barnes
Original date: 11/20/2018

This summer, I had the chance to visit a turkey farm in eastern North Carolina. I’ve worked in agriculture for almost 20 years, but this was my first visit to a turkey farm.The farm has been in the farmer’s family since 1919. Where turkey houses now stand, tobacco once grew. Six years ago, he started growing turkeys under contract with Butterball.I took 15 pages of notes, so choosing only five things to highlight wasn’t easy, but here they are.

Turkeys are not naturally vegetarians.

Like me, you may have seen the label “vegetarian fed” on packages of turkey at the grocery store. It turns out, turkeys are not vegetarians, but omnivores. Turkeys raised on pasture and wild turkeys eat bugs and worms in additional to grass and other vegetation. However, consumer demand for “vegetarian fed” has led companies to add a vegetarian diet option to their feeding program to accommodate what the customer wants while meeting the turkeys’s nutritional needs. Certain flocks (a group of turkeys) are not fed any meat or meat by-products, despite that being what Mother Nature intended them to eat, so they can have “vegetarian fed” on the label.


Turkey Feed


The feed will change approximately 10 times over the course of a turkey’s life to meet its nutritional needs. Turkeys have their own nutritionist, a Butterball employee, who monitors their feed and creates the recipes for each stage of life. Their diet includes vitamins and probiotics. As the nutritionist told us, “Nothing we put in turkey feed can’t be put in my mouth.”

Raising turkeys is a 365-day job, and not just for the farmer.

The farmer told us he comes out to the barns on Christmas morning just like any other day. He can’t leave for a weekend at the beach when he has turkeys on the farm. Every day, the farmer walks through each turkey house at least twice. Each barn has its own set of computers monitoring everything from temperature to feed. A backup system kicks in if the main system fails. His cell phone will get an alert if something is wrong at one of the turkey houses, day or night.

It’s not just the farmer who’s on call. The company veterinarian recalled getting a call about sick turkeys one Sunday morning. He was at the farm later that day to check the turkeys.

Turkeys need a prescription.

No antibiotics are stored on the farm. If a farmer is concerned about one turkey or the entire flock, he contacts his farm’s service technician or the company veterinarian. If treatment is required, the veterinarian writes a prescription, which is sent to the warehouse to be dispersed.

If the entire flock needs treatment, an antibiotic can be added to the water or feed. Strict withdrawal times are observed to make sure the medicine has worked through the turkey’s system before it is sent for processing.

Butterball has a diagnostic lab, which performs autopsies (called a necropsy) on animals that died on the farm to determine cause of death. This information will help the veterinarian decide what course of action, if any, is needed to ensure the remaining turkey’s health.

Just for the record, the only hormones in turkey are the ones they naturally have. In fact, it is illegal to give turkeys, chickens, or other poultry added hormones or steroids.

Young turkeys lose baby feathers.


Turkey Close-up


The turkeys we saw had been on the farm less than a week. When the veterinarian picked one up, I noticed a few spots on it’s body without feathers. I asked about it and learned when turkeys first hatch they have down, or soft, fluffy baby feathers. Turkeys will naturally lose their baby feathers and grow adult feathers. It reminded me of my son losing his baby teeth.

I was also surprised to learn turkeys don’t have feathers on 100% of their body; some areas are naturally featherless.

Turkeys like each other. They really like each other.

Have you seen photos of a turkey house and all the birds are huddled together? You may have thought they were standing close because they didn’t have room to spread out. You’d be wrong.


Turkey House Space


When we walked into the turkey house, I was taken aback by how spacious it is. If you’ve ever walked onto a football field, have you noticed how long it is? The playing field is 100 yards, or 300 feet. This turkey house was twice that; it was 600 feet long. There was a lot of open space, yet the turkeys were all in the same general area. Turns out, turkeys are sociable birds and like to be around each other. Given the choice, they will stick together.

The turkeys gathered around us and moved as a group while we walked through the turkey house. We walked through the middle of the flock, which was like the parting of the Red Sea, but they soon gathered together again. Once they decided we weren’t interesting anymore, they moved away and went back to doing turkey things. The farmer called it “popcorning”, I just called it happy turkeys.