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The Art and Science of Diagnosis of Poultry Diseases

Published: April 23, 2021
By: Dr. Tahseen A. Aziz / Avian pathologist and Diagnostician, Rollins Animal Disease Diagnosis Laboratory, North Carolina Department of Agriculture and Consumer Services, Raleigh, North Carolina, USA.
The definition of disease in the broad context is any deviation from the normal state of health. Diseases can be divided into two broad categories: Infectious and noninfectious. Infectious diseases include those caused mainly by bacteria, viruses, mycoplasmas, fungi, and parasites. Non-infectious diseases can be further divided into three categories: management-related diseases, toxicities, and nutritional diseases (nutritional deficiencies/imbalance). Toxicities and nutritional diseases are self-explanatory.
Management-related diseases (problems) include those caused by errors in the areas of management and house environment such as improper beak trimming, overcrowding, inadequate ventilation, chilling, overheating, poor litter quality, high ammonia level, dusty house environment, poor water quality, and inadequate feeding and/or water space.
Mixed infections with two or more infectious agents are common, and for some diseases, it is the rule rather than the exception. Complex diseases, which result from the interaction of two or more factors (infectious and noninfectious), are also common in poultry flocks.
Performance parameters
For Poultry flocks, healthy birds that are fed balanced feed and managed properly should achieve the “performance goals” for the breed or strain of bird. So, what are the parameters of performance in commercial poultry flocks? For meat-type birds, performance parameters include:
• livability,
• fitness
• daily weight gain,
• feed conversion,
• condemnation rate at processing,
For breeder flocks, parameters mainly include:
• Livability
• fitness
• egg production rate,
• egg quality,
• fertility,
• hatchability,
• quality of the newly hatched birds.
Disease diagnosis
Undoubtedly, diseases have negative impact on the performance of poultry flocks, and so there is a merit in investigating any problem in a poultry flock to provide a diagnosis. Diagnosis means determining the disease. It can also mean determining the cause of a problem in a flock (e.g. poor growth). It is obvious that diagnosis is necessary for controlling a disease or problem in a flock and for preventing it from occurring in the future. Without knowing what the disease or the cause of the problem is, corrective and preventative actions may not be possible. Diagnosis of diseases in commercial poultry flocks is not always an easy task. It is true that some diseases are relatively easy to diagnose based on necropsy findings and/or results of laboratory tests, but some problems need in-depth investigation, determination, and patience. Occasionally, the problem comes and goes without one being able to determine its cause; these problems can be referred to as “unsolved or undiagnosed cases”. One must keep in mind also that the cause of some diseases or problems is still unknown or uncertain.
Diagnosis is a combination of skill science and not guesswork. For most of the poultry diseases that we know today, the diagnostic tools available to the poultry veterinarians generally allow for presumptive and definite diagnosis with a reasonable time. Under field conditions, a presumptive diagnosis in a day is much more important than a final diagnosis in a week. With thousands of birds in a confined space and in close contact with each other, and with multiple houses on the same farm, diseases (especially infectious diseases) can be explosive. Presumptive diagnosis will allow quick intervention to correct or control the problem and mitigate the economic loss. However, and whenever feasible, definite diagnosis should also be sought.
Flock problem
When dealing with a health problem in a poultry flock, poultry diseases must be considered as diseases of a flock rather than of individual birds. Clinical signs in a few individual birds are usually an indication of a problem in the entire flock. To be a competent diagnostician, one would need both knowledge and skills. The following is a guideline for the diagnosis of diseases in commercial poultry flocks.
1. Obtaining a complete case history
In some cases, a clue to the cause of the problem can only be determined from the case history (e.g. toxicity caused by over medication or the use of incompatible drugs). How the clinical history is taken may make the difference between a correct diagnosis, no diagnosis, or a wrong diagnosis. The investigator should not hesitate to ask any question that he or she thinks is relevant to the problem in the flock. A simple, basic question may provide a clue to the cause of the problem in the flock. Poultry veterinarians should have the skills of asking the appropriate questions and meaningfully interpret the answers to them. Clinical history includes:
• age of the birds,
• clinical signs,
• duration and onset of the problem,
• percentage sick,
• mortality record,
• when and where birds are found dead,
• weight for age at various stages of growth,
• egg production at different stages of production,
• feed and water consumption record,
• is the problem in more than one house?
2. Visiting the farm
In some cases, visiting the affected flock(s) may be necessary to observe clinical signs, number of birds affected, distribution of the birds on the floor, stocking density, feed and water system and other house equipment, availability of feed and water, house environment (ventilation, temperature, ammonia, dust, light), and litter condition.
3. Defining the problem and its duration and severity
Now, one must determine the nature of the problem. In other words, what is the problem? Is it clinical signs, mortality, poor growth, drop in egg production, or changes in the egg quality (egg size, egg shape, shell quality)? The problem may be a combination of two or more of the above. If the flock shows clinical signs, then what are the clinical signs? (e.g. loose droppings, respiratory signs, neurological signs, changes in the eye, lameness/leg weakness, egg production problem, etc.).
4. Obtaining additional information about the affected flock(s).
After defining the problem, it may be necessary to obtain additional information that includes but not limited to:
• history of any previous problem in the flock,
• history of a similar problem in previous flocks,
• vaccination record,
• type of feed and water source,
• medication during the last 14 days (in feed or water) including the dose or concentration,
• is the problem associated with a new load of feed?
• any disinfectant is or has been used to sanitize the water lines,
• any pesticide or herbicide is or has been used on the farm,
• management system and daily routine.
5. Necropsy of birds
Necropsy is a very valuable diagnostic tool available to the poultry veterinarians. In many cases, presumptive diagnosis can be made based on necropsy findings and clinical history. For some diseases (e.g. vent pecking, cloacal prolapse, infestation with roundworms), necropsy can provide a final and definite diagnosis. Select a representative group of birds for examination. It is imperative that the selected birds reflect the disease problem. One should keep in mind that in most poultry diseases, not every bird in the flock is affected. Again, think of the disease as the disease of the flock and not of individual birds. If there are clinical signs and mortality, examine freshly dead birds, birds with little clinical signs, and birds with obvious clinical signs. Examine the birds externally before starting the necropsy; for example, check the birds for mite and lice infestation, injuries, lesion in the eyes, ocular and nasal discharge, and soiling of pasting of the vent with fecal materials.
Necropsy includes the following elements: systematic anatomical dissection of the bird, examination of organs and tissues, recognition of abnormalities (lesions) in organs and tissues, interpretation of the abnormalities, and correlating the abnormalities with the problem in the flock.
There is not right or wrong way to perform necropsy on birds, as long as the birds are examined carefully and thoroughly. In order to be consistent, one can develop a set order in which he or she examines the birds to ensure that all organs and tissues are examined. Clinical signs may indicate the need to examine organs or tissues with special care. Be gentle with the organs and tissues during necropsy, as useless pulling and cutting of organs may destroy or obscure lesions of diagnostic significance.
6. Laboratory tests
Samples may be collected for laboratory tests. The kind of samples that need to be collected and the laboratory test(s) to be requested depend mainly on the presumptive diagnosis and/or the abnormalities seen in organs and tissues during necropsy. Samples may be tested or stored for possible future use. It is critical that the samples are collected, handled, stored, and transported properly to keep them useful for laboratory tests. For the diagnosis of most diseases in poultry flocks, samples for laboratory tests usually include one or more of the following:
• tissues or swabs for the isolation of microorganisms or for PCR test,
• blood (serum) samples for serology,
• tissues for histopathology,
• blood or serum samples, tissues, and/or gastrointestinal contents for toxicology,
• feed and water for nutritional analysis or toxicology.
Because some laboratory tests are expensive, any requested laboratory test must be and justifiable, both scientifically and economically.
7. Formulating a diagnosis
Diagnosis of some diseases is like putting together the pieces of a jigsaw puzzle. Clinical history, necropsy findings, and the results of the laboratory tests are assessed and correlated. As mentioned previously, clinical history and necropsy findings will generally provide a presumptive diagnosis. Then it is the job of the poultry veterinarian to evaluate the results of the laboratory tests and correlate them with the clinical history and necropsy findings. The results of the laboratory tests may or may not support the presumptive diagnosis, and if not, then how can the test results be correlated with the clinical history and necropsy findings? In any case, it is now the time to gather all the information and put the different pieces together to formulate a final diagnosis. The final diagnosis may be definite or the best that can be provided. When the results of the laboratory tests are not conclusive, then the poultry diagnostician may have a short list of diseases or causes that he or she suspects. As mentioned previously, some cases may remain undiagnosed. Undiagnosed cases should not be a cause of disappointment but rather a challenge that may trigger further investigation and end up with reporting a disease that has not been reported previously. One must keep in mind that every disease of disease of chickens that we know today was new to someone, sometime, and somewhere. When all's said and done, the chicken producer is interested in one thing: how he or she can correct the problem and prevent it from occurring on his or her farm in the future.
The Art and Science of Diagnosis of Poultry Diseases - Image 1
Related topics:
Tahseen Aziz
Influencers who recommended :
Talaat Al-Alwani, Robert Gauthier
Dr Charles Ibe
22 de noviembre de 2021

This topic is an interesting topic. History findings through owners, flock managers and supervisors is key to inroad into diseases diagnosis. Remember these animals don't talk but you must fix out presumptive diagnosis for further investigations and early treatment to avoid explosion of mortality. I will define disease in every host including man as a state of negative ease. In furtherance to quizzing the attendants dry, an experienced avian veterinarian is cap on the hand on prevalent diseases in the environment in question Viz a Viz Vertical and horizontal transmitted diseases in the environment, age dependant diseases within the environment. With all these his or her calculations on definitive diagnosis is getting close. Then clinical signs and some pathognomonic lesions help matters a lot to build up diagnosis. Further investigations might delay compound matters. Anyway this topic is only meant for field avian veterinarians. Thanks everyone for reading

Dr Kotaiah Talapaneni
Indbro Research & Breeding Farms
9 de octubre de 2021
psedomonas infections respond to gentamycin injection very well.multo tier with belts can create wetness all over. use iodine containing disinfectants to spray at the end of the belt. they act well on psedomonad. ASIPHOR is an iodine based disinfectant
Dr Kotaiah Talapaneni
Indbro Research & Breeding Farms
6 de octubre de 2021
pseudomonas grows in wet litter. your problem at 32weeks may be a contamination afresh, need not be carried from day one. the birds of 32 weeks must be in a different house. if the early infection persisted there should be several bouts of the disease. you may treat the flock with one more course of antibiotic and check the wetness of the bedding and water contamination.
Zahed Abbasi
Toyoor Barekat co
6 de junio de 2021
Hi to all: Disease diagnosis is based on taken of flock history as one aspect like feed and water consumption - daily mortality - respiratory sound ,fecal consistency change in birds behavior and house climate and so on in one and attendant is a good source for taken it .in every house and flock visit , a good clinician must be able to hear attendant . But only an expert practitioner can discover the relation between managemental and house condition and diseases that affect the flock health and performance .
Dr Kotaiah Talapaneni
Indbro Research & Breeding Farms
2 de junio de 2021

Diagnosing poultry diseases can be an art. With closed housing systems with strict biosecurity protocols, the visit of the owner and a vet became need-based. Spotting a problem is based on the data collected. On the contrary, the poultry house attendant spends more time with the birds. A dedicated attendant can spot the disease much earlier than the owner or the vet.

Many poultry diseases/problems are age-specific. In most of the medium and large operations gave separate brooding growing and laying operations in different houses or different premises. Poultry attendants should be allocated with one house for a long time. his observation is more crucial and faster than the owner or the vet.

Taking the example of I.B.D (Gumboro), the disease strikes mostly between 21 and 28 days. A keen attendant can spot sick birds during that age. His prompt reporting is more crucial than the post mortem and laboratory diagnosis.

Coccidiosis is seen more on deep litter and rare in cages. The disease is mostly seen after 4 weeks and before 16 weeks. observing dull birds off fed and bloody droppings is faster than post mortem or the lab.

Water shortage and feeding delays cause much more damage in layer flocks by way of production drops than disease many a times. An alert attendant can diagnose and prevent the problem. Observation on the place of of dead birds in a house pecking are spotted first by the house attendant much earlier.

If the house attendant does not pay attention and misleads the owner and the vet, the diagnosis in poultry can remain a mystery.

DR.R.N.Sreenivas Gowda
Karnataka Veterinary, Animal and Fisheries Sciences University
3 de mayo de 2021

I compliment the author for good analysis, diseases have negative impact on the performance of poultry flocks, the pathologist should have holistic approach in differential diagnosis of poultry health problems.
The definite etiological agents such as Bacteria, Virus, Fungi, and Parasitic infections are well known, but the diagnosis of problems arise from managemental, nutritional and other non infectious causes require skill. I give a classic example of occurrence of coccidiosis in some batches of chicken of same age and same feed. It was a big task to diagnosis. we need to apply our mind here. I visited their feed mill in which they were manufacturing feed on two shifts -day and night. When we analyzed the feed manufactured on night there was outbreaks rather than day time manufacturing feed. This is because of frequent power failure in night time and improper mixing of coccidiostats in the feed. Here we need common sense in diagnosis of such problem. Therefore, the diagnostician should have a holistic approach.

Zahed Abbasi
Toyoor Barekat co
29 de abril de 2021

It is an excellent and short review of diseases diagnosis and you explained it as an expert clinician. In my experiment some diseases are strongly management dependent for example a wrong light program in a layer flock can cause a before peak collapse or post peak dip, and it can be defined as an infectious disease like IB or ND. understanding the real cause needs a long time and good knowledge about poultry biology and light.
I mean it is a complex process to diagnose interference of management and infectious agents and to prevention first needs to correct management item or distinguish them from infectious agent.
Managing poultry diseases needs an expert veterinary practitioner to a jigsaw puzzle.
Thanks so much for your good explanation.

Claudio Afonso
28 de abril de 2021

Excellent summary, Dr. Aziz. Would you be able to expand on what do you think would be the role(s) of NGS, or more specifically, of random metagenomics analysis on avian disease diagnostics?

Suleman Arshad
UVAS, Lahore-Pakistan
4 de diciembre de 2021

Dear all participants,
Hello as disease diagnose is not simple method as it is understood. Basically, we have to practice it for a long time then we able to recognize disease precisely. Some keys point we should keep in mind as follow:
1) Age, it is key thing for diagnose of any disease like infectious diseases.
a)For example in broiler within in first week we observe like Omphlitis, Yolk sack infection, New castle, Infectious bronchitis, Avian influenza, Pullorum disease, Subclinical Infectious bursal disease etc
b) Within second week we observe Avian influenza, Salmonella, IBD, etc.
c) Within third week we observe HPS, IBH, IBD, etc and soon
2) Feed Intake/day, especially this is most important in laying birds like FLHS, CRD, CCRD, etc
3) Production rate or Body weight, as in laying birds or meat the birds production or growth decline due to any infection.
4) Bird behaviour, Is also a key point to understand of susceptibility of any disease.
5) Physical appearance, also give a sign of any infectious agent.

26 de noviembre de 2021
Sir thanks for valuable and very much useful information. Regards
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