Backyard Poultry Primer


What is a galliform?

Order Galliformes consists of heavy-bodied, ground feeding birds like the chicken, turkey, quail, and pheasant. The most common gallinaceous birds encountered in clinical practice are chickens (Gallus gallus) and turkeys (Meleagris gallopavo).


What is a backyard flock?

Backyard or hobby flocks consist of meat and game birds; or ornamental or show birds (Fig 1). One important consideration when working with backyard flocks is to know whether the birds or their eggs will be used as human food as this will impact treatment decisions.

Backyard flock

Figure 1. Most backyard or hobby flocks are owned for meat or egg production. Image by Tabii. Click image to enlarge.

By reason of their small size, noncommercial backyard flocks are not recorded in national databases. The Great Britain Poultry Register does not report flocks less than 50 birds (Smith 2011). The National Animal Health Monitoring System (NAHMS) Poultry 2004 study defined backyard flocks as residences with less than 1,000 birds (Garber 2007), however a survey of backyard flocks in Colorado found that most flocks (68.6%) consisted of less than 50 birds (Smith 2012). The popularity of raising backyard chickens has grown in recent years as an extension of the urban local food or “locavore” movement. In a recent study, it was found that most backyard chicken flocks are owned for meat or egg production (Smith 2012).

Backyard fowl are rarely vaccinated unless the collection is very large; it is a breeding flock; or there is a persistent disease in the flock. Husbandry can also be suboptimal if new owners are unfamiliar with raising poultry.

Taking the history

History for the backyard fowl should include all the standard questions asked for the avian patient as well as vaccination history (Fig 2). Also determine…

  • Is the bird considered a pet or strictly a source of food (Morishita 1999, Harris 2011)?
  • Is the flock open or closed (e.g. exposed to other poultry from bird shows, etc.)?
  • Do caretakers have outside contact with other poultry that could serve as a source of disease?
  • What is the type of food and water source?
  • What is the type of housing?
Consider if the bird is pet or food

Figure 2. Determine during the history if the bird presented is considered a pet or strictly a source of food. Image of ‘Buttercup’ the pet chicken by B. Dubya. Click image to enlarge.

Conditions commonly seen in backyard fowl

Conditions commonly encountered in backyard chickens and turkeys often include endoparasites like Eimeria spp., pasteurellosis or fowl cholera, mycoplasmosis, staphylococcosis, and colibacillosis. Another common presenting problem is trauma, which can typically be categorized as attack wounds or long bone fractures (Murray 2012, Harris 2011) (Fig 3).

Chicken meets cat

Figure 3. Traumatic injury like bite wounds are a common presenting problem for backyard poultry. Image by Steve P. Click image to enlarge.

Below you will find a collection of differential diagnosis lists for common clinical problems observed in the gallinaceous bird. These abbreviated lists should in no way replace professional judgment when evaluating your patient. This “cheat sheet” is merely designed as an aide or reminder system and should never be used for diagnostic decision-making.


Diseases featured in the primer

Avian influenza
Fowl cholera
Lice and mites
Lymphoid leukosis
Marek’s disease virus
Mycoplasma gallisepticum
Mycoplasma synoviae
Newcastle disease virus


The fluffed and ruffled bird

Non-specific signs of illness include fluffed and ruffled plumage, depression, anorexia, and a hunched appearance. Rule-outs for the fluffed and ruffled galliform include:

    • Colibacillosis or Escherichia coli infection in chicks and poults less than or equal to 1 week of age (Fig 4)
      Young chicks

      Figure 4. Colibacillosis is commonly seen in chicks and poults 1 week of age or younger. Image by Ian S.H. Click image to enlarge.

      Colibacillosis refers to any localized or systemic infection caused by avian pathogenic Escherichia coli or APEC. Most APEC isolated from poultry are only pathogenic to birds; these organisms represent a low risk of disease for people and other animals (Saif 2008). Colibacillosis can occur secondary to fecal contamination of eggs causing disease in chicks and poults 1 week of age or younger. Affected birds are lethargic and edematous. If infection involves the yolk sac, then the umbilicus will also appear inflamed (Morishita 1996).

      Colibacillosis can also be transmitted by inhalation or ingestion, which most frequently occurs during cold weather periods when birds are housed indoors. Escherichia coli commonly affects the respiratory tract of both chickens and turkeys, often causing air sacculitis (Morishita 1996). Surviving hens can develop salpingitis and retained eggs. The coelom of affected birds can be greatly distended due to an accumulation of egg debris within the oviduct.

Fowl cholera

The Gram-negative rod Pasteurella multocida causes fowl cholera or avian cholera. Outbreaks of avian cholera are most often reported in chickens, turkeys, domestic ducks, and geese, however other types of gallinaceous birds, companion birds, zoo galliformes, and wild birds including birds of prey can also be infected. Among chickens, death typically occurs in older, laying flocks. Younger birds (less than 16 weeks of age) are relatively resistant. Pasteurellosis is sporadically seen in backyard flocks, especially those with exposure to other poultry through bird shows. Pasteurella multocida isolated from birds with fowl cholera will usually kill rabbits and mice, but other mammals are resistant.

Fowl cholera is classically an acute disease that causes septicemia with high morbidity and mortality rates. Clinical signs can include:

      • Fluffed and ruffled feathers
      • Depression
      • Fever
      • Anorexia
      • Mucoid discharge from the mouth
      • Diarrhea
      • Tachypnea
      • Cyanosis

Cyanosis often develops immediately before death, and is most evident on the unfeathered areas of the head like the comb and wattle. Because the course of disease lasts only a few days, death is sometimes the first finding recognized by owners, especially in turkeys. Survivors of the acute form of fowl cholera can later succumb to debilitation secondary to emaciation and dehydration. Birds can also become chronically infected and recover.

The respiratory tract is an important site of chronic P. multocida infection causing infraorbital sinusitis, tracheal rales, and dyspnea. Clinical signs are can also be related to localized infections. For instance, local infection involving the middle ear and/or cranial bones can cause torticollis. Clinical signs of focal infections can include:

      • Conjunctivitis
      • Exudative pharyngeal lesions
      • Joint and/or foot pad swelling
      • Swollen sternal bursa
      • Swollen wattle (chickens)
      • Torticollis

A tentative diagnosis of acute fowl cholera can be made by demonstrating bipolar organisms in liver imprints using Wright’s stain. Immunofluorescent microscopy can also be used to identify P. multocida in tissue or exudate. Definitive diagnosis relies on isolation of the organism from tissues or blood. Pasteurella spp. can be readily isolated from birds with acute fowl cholera and usually from lesions of chronic cases. The organism is less likely to be grown from debilitated survivors of an acute outbreak. Bone marrow, heart blood, liver, meninges, and focal lesions are preferred samples for culture. Antemortem samples can include choanal swabs, nasal flush samples, or sinus aspirates.

Necropsy findings in acute fowl cholera are associated with vascular disturbances such as petechia, ecchymoses, and generalized hyperemia. Large numbers of bacteria are often seen microscopically within blood vessels.

Antimicrobials are most likely to be successful in the treatment of fowl cholera when they are initiated promptly and based on sensitivity results. Like many Gram-negative organism, strains of Pasteurella can vary in susceptibility to chemotherapeutic agents. Sulfonamides, penicillin, and feeds containing tetracyclines are popular empirical choices.

Newcastle disease virus
Although nine serotypes of avian paramyxovirus (APMV) have been identified, Newcastle disease virus (NDV), or APMV-1, remains the most important pathogen of poultry. Newcastle disease is enzootic in poultry throughout much of Africa, Asia, Central America, and parts of South America. In more developed regions, sporadic epizootics occur on a fairly regular basis. Four worldwide panzootics have been recognized since the disease was first discovered. For this reason, NDV is monitored by the Food and Agriculture Organization of the United Nations as well as the World Organisation for Animal Health (Saif 2008).

Variations in host and virus strains means that clinical disease can range from asymptomatic to severely pathogenic with major economic losses (Table 1).
Table 1. Avian paramyxovirus-1 can be broadly grouped into pathotypes
FormRespiratory signsNeurologic signsEgg productionGastrointestinal signsComments
Viscerotropic velogenic Newcastle disease (VVND)Signs often begin with tachypnea, listlessness, weakness Prior to death, muscle tremors, torticollis, paralysis of legs and wings, opisthotonos can be apparentGreen diarrhea is frequently seen in birds that do not die early in infectionCan cause edema around eyes and head; mortality frequently reaches 100% in flocks of fully susceptible chickens
Neurotropic velogenicSudden onset of severe respiratory diseaseNeurologic signs follow respiratory signs after 1-2 daysEgg production falls dramaticallyDiarrhea is usually absentMorbidity can reach 100%, mortality is generally considerably lower (up to 50% in adults and 90% in juvenile birds has been reported)
MesogenicUsually causes respiratory disease in field infectionsNeurologic signs can occur but are not commonMarked drop in egg production can last for several weeksMortality is usually low except in very young, susceptible birds
LentogenicSerious respiratory disease in young, susceptible birdsDoes not usually cause disease in adults, young birds often die
Avian paramyxovirus is diagnosed by direct detection of viral antigens and/or viral isolation from cloacal or pharyngeal swabs.

Newcastle disease is enzootic in poultry through much of Africa, Asia, Central America, and parts of South America. In more developed regions, sporadic epizootics occur on a fairly regular basis. Four worldwide panzootics have been recognized since the disease was first discovered. For this reason, NDV is monitored by the Food and Agriculture Organization of the United Nations as well as the World Organisation for Animal Health.

Newcastle disease is believed to be transmitted by inhalation or ingestion. Vertical transmission may also occur but this is controversial” (Saif 2008). The spread of virus or methods implicated in epizootics include:

  • Movement of birds

  • Contact with other animals

  • Movement of people and equipment

  • Movement of poultry products

  • Airborne transmission

  • Contaminated feed or water

  • Vaccination

Backyard game fowl, like fighting cocks, have been implicated in outbreaks of NDV in the United State in 1975 and 1998, however the most notable outbreak occurred in southern California in 2002-2003. Although initially seen primarily in backyard game fowl, disease spread to 21 commercial egg-laying flocks. The highest risk factor to these commercial flocks was found to be farm employees exposed to infected backyard flocks.

Newcastle disease also has some zoonotic potential. In humans, the virus can cause unilateral or bilateral conjunctivitis, eyelid edema, epiphora, and subconjunctival hemorrhage. Infections are usually transient.

Reproductive problems

Reproductive problems are a common finding in backyard poultry (Morishita 1995). Clients may not observe or recognize problems in the flock until egg production is influenced. Conditions frequently seen include salpingitis or infection of the oviduct, oviduct impaction, internal laying, and egg binding. Whenever reproductive disease is confirmed or suspected, the history should include:

        • Has there been a drop in egg production?
        • Has there been a change in the external or internal quality of the eggs?

Diseases such as infectious bronchitis in chickens can affect internal as well as external egg quality.

Some birds may be “false layers”. They show the characteristics of egg production, but lay no actual eggs. Reductions in egg laying are a common presenting complaint (Table 2).

Table 2. Important causes of drops in egg production in gallinaceous birds
Husbandry-relatedChange in management
Temperature change
Eggs eaten by predatorsEgg production appears to drop but is in fact normal
Eggs destroyed by penatesEgg production appears to drop but is in fact normal
Viral diseaseNewcastle disease virusChickens, turkeys
Infectious bronchitis virus (coronavirus)Chickens, all ages
Avian influenza
Infectious laryngotracheitis Chickens
Fowl pox
Avian encephalomyelitis
Lymphoid leukosisChickens
Marek’s disease virusChickens
Coronavirual enteritisTurkeys
Eastern equine encephalitis Japanese quail, pheasants
Bacterial diseaseEscherichia coli
Fowl cholera Salpingitis, retained eggs
Mycoplasmosis Salpingitis
Infectious coryzaChicken
Parasitic diseaseEndoparasitesIncluding coccidiosis
Nutritional diseaseCage layer paralysisHigh egg producing breeds like Leghorn chickens may be more susceptible to cage-layer fatigue (Morishita 1999)
Fatty liver hemorrhagic syndrome
Low-salt diet

Birds on commercially prepared feeds are less likely to succumb to nutrition-related diseases (Morishita 1999). “False layers” or abnormal egg production can result from prior infection with infectious bronchitis virus (IBV) in chickens (Morishita 1999). Salpingitis can also occur from prior respiratory disease such as E. coli air sacculitis or colibacillosis (Morishita 1995).

Important rule-outs for external egg changes like misshapen eggs, chalky egg shells, thinly shelled eggs, or shell-less eggs include conditions that affect the oviduct in general and the shell gland or uterus in particular such as:

      • Eimeria spp.
      • Newcastle disease virus
      • Infectious bronchitis virus (chickens)
      • Mycotoxicosis

Mineral imbalances and urolithiasis are also important differentials for external egg abnormalities.

An important cause for internal egg changes like watery egg whites is prior infection with IBV (Morishita 1999).

The roundworm of chickens and turkeys, Ascaridia galli, is a common problem in backyard poultry. Roundworms can occasionally be found in eggs when birds are heavily parasitized. Worms exit the rectum, and then enter the oviduct via the cloaca where they can become incorporated into the egg (Morishita 1995).


Respiratory signs

Important causes of respiratory disease in backyard fowl include fowl cholera, mycoplasmosis, and infectious laryngotracheitis (Fig 5) (Table 3). Infectious laryngotracheitis (ILT) is particularly common in show chickens that come in contact with asymptomatic carrier birds.

Sinusitis in the chicken

Figure 5. Important causes of sinusitis in galliforms include mycoplasmosis, cryptosporidioisis, and pasteurellosis. Image provided by Dr. M. Scott Echols. Click image to enlarge.

Table 3. Important causes of respiratory disease in gallinaceous birds
DiseaseSignalmentClassic clinical presentation
Bordetella avium
(Turkey coryza)
Sporadically seen in backyard turkey
Sneezing (snicking)
Nasal discharge
Tracheal rales
Uncommon in closed flocks
Mycoplasma gallisepticumCommon in backyard chickensNasal discharge
Cough-like sounds
Tracheal rales
Sinusitis is especially common in turkeys, peafowl
Pasteurella multocida (fowl cholera)Adult chickens and turkeysDyspnea and high mortality in the acute form of disease in turkeys
Sinusitis is especially common in turkeys, peafowl
Swollen wattles
Avian influenza Mostly frequently reported in free-flying aquatic birds (ducks, geese, shorebirds, gulls, terns, auks). Sporadically isolated from domestic poultry, most frequently chickens, turkeys, and ducks.Sneezing
Cough-like sound
Infectious bronchitis virus (coronavirus)ChickensNasal discharge
Cough-like sound
Tracheal rales
Internal and external egg quality is also affected
Infectious laryngotracheitis (herpesvirus)Chickens (especially show chickens), pheasants; usually > 5 weeksCough-like sounds
A bloody, mucoid expectorant is produced in severe cases, especially noticeable in white feathered birds
High mortality
Newcastle disease virusMost species of domestic, aviary, and free-ranging birds have been found to be susceptible. Lentogenic and mesogenic strains are common in domestic fowl in the United States.Cough-like sounds
(wet form)
All species of birds are susceptible to some strain of pox. Diphtheritic lesions frequently occur in infected pheasants and quail.White nodules or caseous plaques on mucosa of oropharynx, larynx, trachea cause dyspnea, high mortality
CryptosporidiosisTurkey, quailSneezing
Cough-like sounds
Tracheal rales
High mortality in quail
Tracheal worms or gapeworms Genus Syngamus (chickens, turkeys, pheasants, peafowl); Cyathostoma (turkeys)Tracheal rales
Flicking or head shaking

Aspergillosis can also be seen in Order Galliformes, but is rarely a primary pathogen in backyard flocks.


Mycoplasma gallisepticum

The most common cause of chronic respiratory disease (CRD) in chickens and infraorbital sinusitis in turkeys in Mycoplasma gallisepticum. Mycoplasma gallisepticum is common in backyard chickens. The onset of disease is often insidious. Clinical signs can include non-specific signs of illness, tracheal rales, cough, nasal discharge, conjunctivitis, and a drop in egg production. Foamy eye secretions may also be observed in turkeys. Clinical signs can also be more pronounced with concurrent E. coli or infectious laryngotracheitis infection. Disease can be transmitted through eggs obtained from non-commercial poultry sources. Mycoplasmosis tends to be variable in severity and duration, but it is typically more severe and prolonged during the colder months. Disease is also more severe in younger birds.


Avian influenza

Avian influenza (AI) viruses have a worldwide distribution. The most frequent reports of AI occur in free-ranging aquatic birds like waterfowl, shorebirds, gulls, and terns, which are considered reservoirs of AI viruses (Saif 2008). In fact, dabbling ducks like the mallards (Anas platyrhynchos) have the highest reported isolation rates of AI viruses. Up to 60% of juvenile mallard ducks are infected prior to late summer migration.

Gallinaceous birds are not natural reservoirs of AI viruses. Avian influenza has been sporadically isolated from domestic fowl, most frequently chickens, turkeys, and domestic ducks. Most influenza infections in domestic poultry have been from avian-origin influenza viruses, however H1N1, H1N2, and H3N2 swine influenza viruses have infected turkeys, especially turkey breeders.

In recent years, outbreaks of highly pathogenic avian influenza (HPAI) viruses have caused the death of millions of poultry and of more than 200 humans worldwide (Bavinck 2009). Fortunately research suggests that backyard fowl have played a marginal role in recent outbreaks of highly pathogenic avian influenza in commercial flocks (Smith 2011, Bavinck 2009)

Avian influenza replicates within the respiratory, intestinal, renal and/or reproductive organs. Virus can be shed from the nares, mouth, conjunctiva, and cloaca of infected birds. Virus is transmitted by direct contact or through indirect exposure to virus-contaminated fomites.

Morbidity and mortality rates are variable in poultry, and depend on virus pathogenicity and the host. Clinical findings can include:

      • Oculonasal discharge
      • Infraorbital sinusitis
      • Dyspnea, tachypnea
      • Cyanosis
      • Edema of the head, comb, and wattle
      • Subcutaneous ecchymotic hemorrhages of the legs and feet
      • Blood-tinged oral and nasal discharges
      • Green diarrhea
      • Torticollis, opisthotonos, ataxia

Avian influenza viruses can be commonly recovered from tracheal, oropharyngeal, or cloacal swabs from live or dead birds. Definitive diagnosis of AI relies on viral isolation or direct detection of AI viral proteins or genes in specimens like tissues, swabs, cell cultures, or embryonating eggs.


Oropharyngeal plaques

Important rule-outs for oropharyngeal plaques in the galliform include:

Candida albicans overgrowth usually occurs secondary to prolonged antibiotic use or in poultry raised under harsh environmental conditions.



There are many infectious agents that can cause enteritis in galliforms. Important differential diagnoses include:

      • Eimeria spp:  Coccidiosis is common in chickens and turkeys raised on dirt floors. Heavy loads can lead to bloody diarrhea. Different species affect different parts of the intestinal tract, with some species like Eimeria tenella affecting only the cecum to cause hemorrhagic typhlitis and cecal core formation. Disease can be complicated by infection with E. coli or Clostridium perfringens (necrotic enteritis).
      • ColibacillosisEscherichia coli has been associated with enteritis, but more research is needed to determine the actual role in typhlitis and cecal core development (Morishita 1996).
      • Histomoniasis
      • Lymphoid leukosis:  Lymphoid leukosis is a retroviral infection that causes tumors in chickens 14 weeks of age and older. The incidence of avian leukosis is typically low (<4%), however, mortality can be high in affected birds. Lymphoid leukosis is transmitted transovarially; hens shed virus into eggs. Chicks are then infected at hatch and shed virus their entire lives. Necropsy findings include profound hepatomegaly, bursal enlargement, and neoplastic nodules. Unlike Marek’s disease virus, neural involvement does not occur in lymphoid leukosis.
      • Pasteurella multocida:  Fecal material is initially watery and white in acute fowl cholera, but later becomes green and mucoid (Table 4).
      • Coronaviral enteritis is an acute, highly contagious disease of turkeys.

Table 4. Stool color or consistency as a clue to underlying cause of disease
Stool color or appearance Differential diagnoses
Bloody diarrhea

  • Acute coliform enteritis

  • Clostridium colinum or ulcerative enteritis (quail, chickens, turkeys, pheasants, grouse, etc.)

  • Hemorrhagic enteritis or type II adenovirus (turkeys)

  • Infectious bursal or Gumboro disease (birnavirus)(chickens)

  • Histomoniasis (turkeys)

  • Coccidiosis (Eimeria spp.)


  • Coronaviral enteritis

  • Protozoal disease

(Bacillary white diarrhea)

  • Pullorum disease (Salmonella pullorum)*

  • Chilled birds


  • Yellow urates

  • Erysipelas

  • Fowl cholera

  • Salmonella gallinarum (fowl typhoid)

  • Chlamydiosis

  • Histomoniasis (sulfur-colored stool in turkeys)

* Once the most important disease in poultry, Pullorum disease is now one of the least significant.


Histomoniasis is caused by the protozoan Histomonas meleagridis. Histomoniasis has a complex life cycle that involves the earthworm and common cecal worm, Heterakis gallinarum. Visit Wildpro for a diagram illustrating the H. meleagridis life cycle.

Histomoniasis can be a serious disease in backyard turkeys. Disease is usually less severe in chickens and in fact, chickens can be an asymptomatic source of Histomonas sp. and Heterakis sp. Turkeys can contract disease by ingesting the protozoan from fresh droppings. Research suggests that contaminated water can also play a role in parasite transmission (Loft 2012).

Histomonas mainly affects the ceca and liver. An early sign in turkeys is sulfur-colored droppings. Affected birds can also display non-specific signs of illness. Most turkeys die acutely or after a more prolonged course of disease (McDougald 2005). Characteristic lesions found at necropsy include circular depressions surrounded by raised, craterlike lesions in the liver and cores of caseated debris in the cecum. Histomoniasis can also be found in the bursa of Fabricius, kidney, spleen, and other tissues (Saif 2008). Antemortem diagnosis relies of identification of the organism on fecal exam (Morishita 1996).

In commercial flocks, histomoniasis was relatively well controlled until the ban on nitroimidazole antihistomonals in the United States and Europe in the 1990s. There is currently no product available for treatment of blackhead disease (Saif 2008).


Neurologic disease

Marek’s disease virus is a highly infectious disease caused by a herpesvirus. While commercial poultry are vaccinated against Marek’s disease virus (MDV) at 1 day of age, disease occurs frequently in backyard chickens. Although less than 14 weeks is frequently listed in the literature, unvaccinated birds of any age can develop MDV. In fact, the common history is exposure to birds of unknown vaccination history.

There are four clinical forms of MDV (Table 5). The visceral form is difficult to distinguish from lymphoid leukosis. Marek’s disease virus is an important cause of neurologic disease in backyard poultry (Table 6). In the neurologic form, MDV is often first noticed as gait disturbances like ataxia or stilted movements. As MDV progresses, birds can exhibit range paralysis in which one leg is stretched forward and the other leg is stretched back. Unilateral enlargement of the sciatic nerve is identified at necropsy.

Table 5. Forms of Marek’s disease virus
FormsClinical disease
CutaneousWhite, distinct nodules involving feather follicles
NeurologicAtaxia, stilted gait, range paralysis
OcularBlue-gray discoloration of iris
VisceralLymphoid tumors of liver, spleen
Tumors can also occur in heart, kidneys, intestines

Table 6. Differential diagnoses for central neurologic signs in gallinaceous birds
Bacterial diseaseArizonosis (turkeys)
Fowl cholera
Viral diseaseAvian encephalomyelitis
Avian influenza
Eastern equine encephalitis (ataxia, paresis, paralysis, and/or torticollis in pheasants or Japanese quail)
Marek's disease virus
Newcastle disease virus
Parasitic diseaseBaylisascaris
Fungal diseaseAspergillosis
Nutritional diseaseThiamine deficiency
Vitamin E deficiency
Other non-infectious diseasesBotulism
Heavy metal toxicity

Important causes of peripheral neurologic signs gallinaceous birds include:

      • Marek’s disease virus (chickens)
      • Botulism
      • Trauma


Differential diagnoses for swollen leg joints and footpads in galliforms include:

      • Fowl cholera (localized infections of leg or wing joints)
      • Mycoplasmosis
      • Staphylococcus aureus:  Staphylococcus arthritis is common in poultry raised on wet litter or rough wire surfaces. Infection can involve not only leg joints and footpads, but also tendon sheaths.
      • Viral arthritis (reoviruses)
      • Gout
      • Rat-bite infection
      • (Erysipelas)

Mycoplasma synoviae

Infections caused by Mycoplasma synoviae are less common than M. gallisepticum. Acute infection is generally seen in 4-16 week-old chickens and 10-24 week old turkeys, although natural infection has been observed in chicks as young as 6 days of age. Local Mycoplasma synoviae infection most frequently causes upper respiratory infection in chickens. Systemic M. synoviae infection causes acute to chronic tenosynovitis or bursitis.

Early clinical signs of infectious synovitis in chickens typically include lameness, retarded growth, and a pale comb. Additional clinical signs can include:

      • Non-specific signs of illness like lethargy
      • As disease progresses, feathers become ruffled and the comb shrinks in size. In some cases, the comb will appear blue-red.
      • Warm, fluctuant swellings of one or more joints are usually found. Hock joints and footpads are most commonly involved but in some birds most joints are affected.
      • Enlargement or swelling of the sternal bursa or “breast blisters”.
      • Most birds continue to eat and drink if food and water are placed nearby, however severely affected birds lose weight.
      • Mortality is usually less than 1%.

Respiratory signs are rarely observed in turkeys. Other clinical signs in turkeys, are similar to those seen in chickens. Lameness is the most prominent finding, however joint swelling may not be as prominent as in chickens.

A presumptive diagnosis of M. synoviae infection can be based on clinical signs. A definitive diagnosis can be made by isolation and identification of the organism. Mycoplasma synoviae is easily cultured from acutely infected joints, but in chronic infections viable organisms may no longer be present in lesions. Isolation from the upper respiratory tract is more reliable in chronically infected birds. Mycoplasma can also be directly detected in tissues or culture medium using DNA probes.

Mycoplasma synoviae is readily transmitted vertically (through the egg) or horizontally therefore the only effective control is to select chickens or turkeys from specific-pathogen free flocks.

Gastrocnemius tendon displacement or perosis is another potential problem in young, growing birds. Perosis may be caused by diets deficient in biotin, folic acid, niacin, or pyridoxine. Other potential causes of lameness include “curly toe paralysis” caused by riboflavin deficiency, pathologic fractures, and rickets. Additionally early in disease, it can be difficult to distinguish lameness from ataxia, so differentials such as Marek’s disease virus must also be considered (see neurologic disease above).


Skin lesions

Knemidokoptes mutans, or the scaly leg mite, can be found in backyard poultry, particularly chickens. Crusty, raised lesions are most frequently found on the legs, but can also appear on the comb and wattles.

Poxvirus lesions also occur on the unfeathered skin of the legs and face of backyard poultry, especially chickens. These yellow pustules, vesicles, or brown scabs and crust appear quite different from Knemidokoptes (Morishita 1999). The causative agent is most often fowl pox, but turkey pox can also be encountered.

Pasteurella multocida can be responsible for localized infection of the wattles, comb, or the subcutaneous tissues of the head (Christensen).


Feather loss

Important rule outs for feather loss in gallinaceous birds include: (Morishita 1999)

      • Ectoparasites
      • Molting
      • Mating
      • Feather destructive behavior

Lice are common parasites in backyard chickens and turkeys (Table 7). Infestations cause rough feathering. When feathers are parted, lice can often be seen scurrying away. Lice eggs can be found as white deposits at the base of feather shafts (Morishita 1999). Egg clusters or nits can also be palpated, especially over the ventral coelom and near the vent.

Table 7. Distinguishing lice and mites
Size (mm)1-6 (length)~0.5 (diameter)
Egg locationBase of featherAlong feather shaft

Mites are small, black organisms that resemble ground pepper. Mites often lay eggs along the midshaft of the feather, which appear as blackened areas along the feather shaft. Mites and mite egg-encrusted feathers are particularly noticeable on the ventral coelom and vent.


Ophthalmic disease

Important differentials for conjunctivitis in backyard fowl include: (Morishita 1999)

It is also important to remember that the ocular form of Marek’s disease virus causes blue-to-gray discoloration of the iris, usually in birds less than 14 weeks of age (Morishita 1996).


Peracute or acute death

When confronted with a complaint of sudden death in backyard fowl, important differentials include:

      • Wet pox (dyspnea, death)
      • Fowl cholera, particularly in turkeys
      • Colibacillosis, chicks and poults
      • Tracheal worms
      • Trauma


Forming a differential diagnosis list for the gallinaceous bird follows the same principles as in any other species, however some diseases are relatively unique, or at least much more common, in this taxonomic group. The minimum database frequently includes fecal parasite testing (flotation and saline preparation), hematology, plasma biochemistry, and survey radiographs. Serologic tests and culture can also be used to detect various disease agents. Also keep in mind that is easy for poultry owners to medicate their birds before seeking help. This can butt the diagnostic picture and make recovery of the disease agent more difficult (Morishita 1999).

Be sure to consider the health of the entire flock and to remain vigilant for important poultry disease. Although the majority of small flocks appear to pose little risk of disease transmission because they are maintained in semi-isolation (Burns 2011), there is a potential for backyard flocks to play a role in the spread of infectious diseases within poultry populations as well as the transmission of zoonotic diseases to humans (Smith 2012).




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Morishita TY. Clinical assessment of gallinaceous birds and waterfowl in backyard flocks. Vet Clin North Am Exot Anim Pract 2(2):383-403, 1999.

Morishita TY. Common infectious diseases in backyard chickens and turkeys (from a private practice perspective). J Avian Med Surg 10(1):2-11, 1996.

Morishita TY. Common reproductive problems in the backyard chicken. Proc Annu Conf Assoc Avian Vet 1995. Pp. 465-467.

Murray JK. Backyard Poultry 101 for the Veterinary Technician. Proc Annu Conf Assoc Avian Vet 2012. Pp. 93-97.

Peterson A, Christensen JP, Kuhnert P, et al. Vertical transmission of a fluoroquinolone-resistant Escherichia coli within an integrated broiler operation. Vet Microbiol 116(1-3):120-128, 2006.

Ritchie BW. Avian Viruses: Function and Control. Lake Worth, FL: Wingers Publishing; 1995.

Saif YM, Fadly AM, Glisson JR (eds). Diseases of Poultry, 12th ed. Wiley-Blackwell, 2008.

Smith EI, Reif JS, Hill AE, et al. Epidemiologic characterization of Colorado backyard bird flocks. Avian Dis 56(2):263-271, 2012.

Smith G, Dunipace S. How backyard poultry flocks influence the effort required to curtail avian influenza epidemics in commercial poultry flocks. Epidemics 3(2):71-75, 2011.

Additional resources

For more information on poultry medicine, visit Ohio State University’s Ohio Line for articles authored or co-authored by Dr. Morishita:

To cite this page:

Morishita T, Pollock C. Backyard poultry primer. November 28, 2012. LafeberVet Web site. Available at