Parrot Dietary Habits and Consumption of Alternate Foodstuffs.

Inappropriate diets cause many of the health problems commonly reported in parrots by psittaculturists and veterinarians. The dietary management of captive parrots would benefit from information derived from studies of dietary habits of wild parrots; however, it is unclear how complete this body of knowledge is at this time. Documentation of parrots' dietary habits appears to have grown dramatically over the past century. Reports of parrots consuming a number of foodstuffs beyond the reproductive parts of plants (alternate foodstuffs) have increased. The extent of alternate foodstuffs in parrot diets is currently unknown. We used Google search engines (ie, Scholar, Videos, Images) to determine how well psittaciform dietary habits have been studied to date and to quantify reports of alternate foodstuffs consumption among genera of Psittaciformes. We found that the dietary habits of over 43% of parrot species are poorly resolved. The dietary habits of 71.5% of parrot species classified by the International Union for Conservation of Nature as at risk of extinction are not well resolved. Parrots' consumption of alternate foodstuffs occurred at the following rates at the genus level: 91.2% foliage, 76.9% terrestrial invertebrates and fine earthen materials, 74.7% wood, 44% pure minerals, 34.1% vertebrates (9.9% dung), 29.7% sap, 19.8% roots, 17.6% charcoal, 18.7% epiphytes, 16.5% coarse earthen materials, 8.8% algae, and 6.6% aquatic invertebrates. Of these reports, 79.1% involved observations of wild parrots. Many parrot species may be more omnivorous than previously realized. Alternate foodstuffs are generally absent from current veterinary-based dietary recommendations for captive parrots. Future studies are needed to determine whether providing alternate foodstuffs to captive parrots can be used as a means to improve their diets and thus their health, welfare, and reproductive success.

Immunophenotype of the inflammatory response in the central and enteric nervous systems of cockatiels (Nymphicus hollandicus) experimentally infected with parrot bornavirus 2.

Proventricular dilatation disease is a lethal disease of psittacine birds. In this study, we characterized the local cellular immune response in the brain, proventriculus, and small intestine of 27 cockatiels (Nymphicus hollandicus) experimentally infected with parrot bornavirus 2 (PaBV-2). Perivascular cuffs in the brain were composed of CD3+ T-lymphocytes and Iba1+ macrophages/microglia in most cockatiels (n = 26). In the ganglia of the proventriculus, CD3+ T-lymphocytes (n = 17) and Iba1+ macrophages (n = 13) prevailed. The ganglia of the small intestine had a more homogeneous distribution of these leukocytes, including PAX5+ B-lymphocytes (n = 9), CD3+ T-lymphocytes (n = 8), and Iba1+ macrophages (n = 8). Our results indicate that perivascular cuffs in the brain and the inflammatory infiltrate in the proventriculus of PaBV-2-infected cockatiels is predominately composed of T-lymphocytes, while the inflammatory infiltrates in the ganglia of the small intestine are characterized by a mixed infiltrate composed of T-lymphocytes, B-lymphocytes, and macrophages.

Normative ocular data for juvenile and adult Japanese quail (Coturnix japonica).

OBJECTIVE: To obtain normative ocular data for Japanese quail as they mature from juveniles to adults. ANIMALS STUDIED: Twenty-six captive Japanese quail comprising thirteen males and thirteen females, free of ocular disease, were included in the study. PROCEDURES: Ophthalmic reference values were measured in both eyes at 1 and 5 months of age. A complete ophthalmic examination was performed, including neuro-ophthalmic reflexes, slit lamp biomicroscopy, phenol red thread test (PRTT), rebound tonometry, fluorescein staining, horizontal corneal diameter measurement, indirect ophthalmoscopy, and ocular ultrasound biometry. Ultrasound biomicroscopy measurements of axial globe length, lens thickness, vitreal chamber length, and pecten length were recorded. The depth of the anterior chamber was calculated by subtracting the lens thickness and vitreous length from the axial globe length. Measures of association and descriptive statistics were analyzed using STATA-14 and STATA-15. RESULTS: Juvenile and adult females were heavier than age-matched males. Weight, intraocular pressure, horizontal corneal diameter, axial globe length, and lens thickness measurements increased with age. No statistically significant differences were found in the remainder of measurements among individuals in different sex or age-groups. CONCLUSIONS: This work provides reference values and clinical findings that can be used in future research on quail and ocular disease.

Distribution of Viral Antigen and Inflammatory Lesions in the Central Nervous System of Cockatiels ( Nymphicus hollandicus) Experimentally Infected with Parrot Bornavirus 2.

Neurotropism is a striking characteristic of bornaviruses, including parrot bornavirus 2 (PaBV-2). Our study evaluated the distribution of inflammatory foci and viral nucleoprotein (N) antigen in the brain and spinal cord of 27 cockatiels ( Nymphicus hollandicus) following experimental infection with PaBV-2 by injection into the pectoral muscle. Tissue samples were taken at 12 timepoints between 5 and 114 days post-inoculation (dpi). Each experimental group had approximately 3 cockatiels per group and usually 1 negative control. Immunolabeling was first observed within the ventral horns of the thoracic spinal cord at 20 dpi and in the brain (thalamic nuclei and hindbrain) at 25 dpi. Both inflammation and viral antigen were restricted to the central core of the brain until 40 dpi. The virus then spread quickly at 60 dpi to both gray and white matter of all analyzed sections of the central nervous system (CNS). Encephalitis was most severe in the thalamus and hindbrain, while myelitis was most prominent in the gray matter and equally distributed in the cervical, thoracic, and lumbosacral spinal cord. Our results demonstrate a caudal to rostral spread of virus in the CNS following experimental inoculation of PABV-2 into the pectoral muscle, with the presence of viral antigen and inflammatory lesions first in the spinal cord and progressing to the brain.

Comparative Cytogenetics of the Congo African Grey Parrot (Psittacus erithacus).

The Congo African grey parrot (Psittacus erithacus, PER) is an endemic species of Central Africa, valued for its intelligence and listed as vulnerable due to poaching and habitat destruction. Improved knowledge about the P. erithacus genome is needed to address key biological questions and conservation of this species. The P. erithacus genome was studied using conventional and molecular cytogenetic approaches including Zoo-FISH. P. erithacus has a 'typical' parrot karyotype with 2n = 62-64 and 8 pairs of macrochromosomes. A distinct feature was a sharp macro-microchromosome boundary. Telomeric sequences were present at all chromosome ends and interstitially in PER2q, the latter coinciding with a C-band. NORs mapped to 4 pairs of microchromosomes which is in contrast to a single NOR in ancestral type avian karyotypes. Zoo-FISH with chicken macrochromosomes GGA1-9 and Z revealed patterns of conserved synteny similar to many other avian groups, though neighboring synteny combinations of GGA6/7, 8/9, and 1/4 were distinctive only to parrots. Overall, P. erithacus shared more Zoo-FISH patterns with neotropical macaws than Australian species such as cockatiel and budgerigar. The observations suggest that Psittaciformes karyotypes have undergone more extensive evolutionary rearrangements compared to the majority of other avian genomes.

The genome sequence of parrot bornavirus 5.

Although several new avian bornaviruses have recently been described, information on their evolution, virulence, and sequence are often limited. Here we report the complete genome sequence of parrot bornavirus 5 (PaBV-5) isolated from a case of proventricular dilatation disease in a Palm cockatoo (Probosciger aterrimus). The complete genome consists of 8842 nucleotides with distinct 5' and 3' end sequences. This virus shares nucleotide sequence identities of 69-74 % with other bornaviruses in the genomic regions excluding the 5' and 3' terminal sequences. Phylogenetic analysis based on the genomic regions demonstrated this new isolate is an isolated branch within the clade that includes the aquatic bird bornaviruses and the passerine bornaviruses. Based on phylogenetic analyses and its low nucleotide sequence identities with other bornavirus, we support the proposal that PaBV-5 be assigned to a new bornavirus species:- Psittaciform 2 bornavirus.

Characterization of a new genotype of avian bornavirus from wild ducks.

BACKGROUND: Avian bornaviruses (ABV) are a recently described group of intranuclear negative-stranded RNA viruses (Order Mononegavirales, Family Bornaviridae). At least 13 different ABV genotypes have been described. One genotype, the Canada goose genotype (ABV-CG), has been isolated from geese and swans and is widely distributed across North America. RESULTS: We have isolated and characterized a previously undescribed genotype of avian bornavirus from the brains of wild ducks. This new genotype, provisionally designated ABV genotype MALL, was detected in 12 of 83 mallards, and 1 of 8 wood ducks collected at a single location in central Oklahoma. The virus was cultured on primary duck embryo fibroblasts, fragments were cloned, and its genome sequence of 8904 nucleotides determined. This new genotype has 72% nucleotide identity and 83% amino acid identity with the ABV-CG genotype previously shown to be present in geese and swans. Histologic and immunohistochemical examination of the brains and eyes of four positive ducks indicated the presence of virus-infected neurons and glia in their cerebrums and retinas in the absence of inflammation. CONCLUSIONS: More than one genotype of ABV is circulating in North American waterfowl. While the infected ducks were not observed to be suffering from overt disease, based on the immunohistochemistry, we speculate that they may have suffered some visual impairment.

Evaluation of Multidrug Therapy With Azithromycin, Rifampin, and Ethambutol for the Treatment of Mycobacterium avium subsp avium in Ring-neck Doves (Streptopelia risoria): An Uncontrolled Clinical Study.

An uncontrolled clinical study was conducted to evaluate the efficacy of a multidrug protocol in 16 ring-neck doves ( Streptopelia risoria ) from a flock naturally infected with Mycobacterium avium subsp avium. The doves were considered infected on the basis of a high prevalence of infection in a group of 29 birds that were euthanatized from the same flock and clinical signs and pathologic results consistent with infection in the remaining birds. All birds were treated with azithromycin (43 mg/kg), rifampin (45 mg/kg), and ethambutol (30 mg/kg) administered orally once daily for 180 days. Five birds died during treatment and were confirmed positive for mycobacteriosis on postmortem examination. Of the remaining 11 birds, infection and disease were present in 9 (81.8%) at the end of the treatment. Postmortem investigation showed that 2 mycobacterial isolates were resistant to ethambutol, intermediately sensitive to rifampin, and sensitive to azithromycin. Microscopic examination of liver sections equivalent of those that would be taken for biopsy showed that biopsy as a method of monitoring birds for treatment success had poor sensitivity. Toxicity associated with drug therapy was not observed in these doves nor in 6 outwardly healthy ring-neck doves exposed to the same treatment. The results of this study showed that this protocol of azithromycin, rifampin, and ethambutol has poor efficacy when administered for 180 days for treatment of doves infected with M avium subsp avium.

Complete genome sequence of avian bornavirus genotype 1 from a Macaw with proventricular dilatation disease.

Avian bornaviruses (ABV) were first detected and described in 2008. They are the etiologic agents of proventricular dilatation disease (PDD), a frequently fatal neurologic disease of captive parrots. Seven ABV genogroups have been identified worldwide from a variety of sources, and that number may increase as surveillance for novel bornaviruses continues. Here, we report the first complete sequence of a genogroup 1 avian bornavirus (ABV1).

Detection and characterization of a distinct bornavirus lineage from healthy Canada geese (Branta canadensis).

Avian bornaviruses (ABV), identified in 2008, infect captive parrots and macaws worldwide. The natural reservoirs of these viruses are unknown. Reverse transcription-PCR (RT-PCR) was used to screen oropharyngeal/cloacal swab and brain samples from wild Canada geese (Branta canadensis) for ABV. Approximately 2.9% of swab samples were positive for bornavirus sequences. Fifty-two percent of brain samples from 2 urban flocks also tested positive, and brain isolates were cultured in duck embryo fibroblasts. Phylogenetic analyses placed goose isolates in an independent cluster, and more notably, important regulatory sequences present in Borna disease virus but lacking in psittacine ABVs were present in goose isolates.

Positive reinforcement training facilitates the voluntary participation of laboratory macaws with veterinary procedures.

Psittacine birds are challenging laboratory subjects, as they are typically long-lived, very social, highly intelligent, and easily stressed. The benefits of positive reinforcement techniques in animal management have been well documented for mammalian species; however, there are few publications on such programs for birds. To demonstrate the practicality of positive reinforcement training of laboratory birds to cooperate with research procedures involving direct manipulation of individuals, 9 adult macaws (Ara species; 5 individuals and 2 pairs) were trained in 10-minute sessions, twice a day for 8 weeks. The trained behaviors were: target, stay, accept liquids from a syringe, step onto a perch, step onto a scale, allow pressing a syringe to the pectoral area (surrogate for an intramuscular injection), and step onto a towel. All individually housed birds reliably targeted, stayed, and accepted a syringe, and 4 of the 5 stepped onto a perch. One bird performed all of the behaviors. Paired birds learned advanced techniques significantly faster when trained by 2 trainers versus 1 trainer. All behaviors that were mastered during the initial phase of training were successfully transferred so that the birds would reliably perform for the husbandry staff. We conclude that positive reinforcement techniques provide an effective, practical way to train laboratory macaws in behaviors useful for veterinary practice and research. Positive reinforcement used to evoke voluntary participation in procedures will help reduce stress associated with capture and restraint and improve welfare for laboratory parrots.

The detection of avian bornavirus within psittacine eggs.

Avian bornavirus (ABV) is a known cause of proventricular dilatation disease in parrots and encephalitis in waterfowl and is a significant cause of both morbidity and mortality in captive birds. Transmission is thought to occur primarily by the fecal-oral route. In an aviary setting, controlling the disease involves a thorough understanding of the complete transmission cycle, including determining whether vertical transmission occurs. In this study, vertical transmission of ABV was evaluated by using 61 eggs obtained from birds in 2 aviaries where proventricular dilatation disease was prevalent, and the presence of ABV had been confirmed by fecal reverse transcription-polymerase chain reaction by using a primer set designed to detect ABV M protein. The contents of these eggs were then tested for the presence of ABV RNA. Of the eggs tested, 10 were determined to contain ABV RNA. These eggs ranged from apparently nonviable to those that contained developing embryos. ABV was detected in the brain tissue of 2 embryos. It remains to be proven that infected chicks can hatch from these eggs to complete the vertical transmission cycle; however, these findings suggest that vertical transmission of ABV may occur.

Proventricular dilatation disease in cockatiels (Nymphicus hollandicus) after infection with a genotype 2 avian bornavirus.

An isolate of genotype 2 avian bornavirus (ABV) was recovered from a cockatiel (Nymphicus hollandicus) that was euthanatized for an unrelated lesion and showing no clinical evidence of proventricular dilatation disease (PDD). On histopathologic examination, mild inflammatory lesions were present in the heart and brain, but gastrointestinal lesions characteristic of classic PDD were not observed. To investigate if this ABV2 isolate had reduced virulence, the virus was propagated in duck embryo fibroblasts and inoculated into 2 adult cockatiels by the oral and intramuscular routes. One bird developed clinical signs on day 33 and was euthanatized on day 36. The second challenged bird developed clinical signs on day 41 and was euthanatized on day 45. At necropsy, the proventriculus of both birds was slightly enlarged. Histopathologic examination showed lesions typical of PDD in the brain, spinal cord, heart, adrenal gland, and intestine. A control, uninoculated cockatiel was apparently healthy when euthanatized on day 50. These results show that ABV2 is now the second ABV genotype to be formally shown to cause PDD.

The olfactory system: the remote-sensing arm of the immune system.

Odors may be pleasant or unpleasant and in practice, pleasant odors are attractive while unpleasant odors are repellent. However, an odor that is noxious to one species may be attractive to another. Plants, predators, and pathogens may enhance their transmission by manipulating these signals. This may be especially significant when odors attract arthropod disease vectors. Odor detection may also be important in small prey species for evasion of macropredators such as large carnivores. Conversely, pleasant odors may identify family members, parents, or sexual partners. They may also generate signals of good health or fitness and contribute to the process of mate selection. In this review, we seek to integrate these odor-driven processes into a coherent pattern of behaviors that serve to complement the innate and adaptive immune systems. It may be considered the 'behavioral immune system'.

Use of avian bornavirus isolates to induce proventricular dilatation disease in conures.

Avian bornavirus (ABV) is a newly discovered member of the family Bornaviridae that has been associated with the development of a lethal neurologic syndrome in birds, termed proventricular dilatation disease (PDD). We successfully isolated and characterized ABV from the brains of 8 birds with confirmed PDD. One isolate was passed 6 times in duck embryo fibroblasts, and the infected cells were then injected intramuscularly into 2 healthy Patagonian conures (Cyanoliseus patagonis). Clinical PDD developed in both birds by 66 days postinfection. PDD was confirmed by necropsy and histopathologic examination. Reverse transcription-PCR showed that the inoculated ABV was in the brains of the 2 infected birds. A control bird that received uninfected tissue culture cells remained healthy until it was euthanized at 77 days. Necropsy and histopathologic examinations showed no abnormalities; PCR did not indicate ABV in its brain tissues.

Comparison of sampling methods, culture, acid-fast stain, and polymerase chain reaction assay for the diagnosis of mycobacteriosis in ring-neck doves (Streptopelia risoria).

Even when different diagnostic modalities are available, mycobacteriosis is difficult to diagnose in a live bird. To investigate the diagnostic value of sampling different tissues and using different diagnostic methods, we evaluated results of mycobacterial culture, Ziehl-Neelsen (ZN) staining, and single-amplification polymerase chain reaction assay (PCR) of 18 ring-neck doves (Streptopelia risoria) with confirmed natural infection with Mycobacterium avium avium. Results of testing liver biopsy, duodenal aspirate, and bone marrow aspirate samples and liver and spleen samples collected at necropsy were compared. Results showed the use of one single technique did not allow identification of all infected birds. In liver biopsy and bone marrow aspirate samples, culture had the highest sensitivity, whereas PCR assay and ZN staining had low sensitivity, and their combination was less sensitive than culture alone. Examination of ZN staining of the intestinal aspirate samples failed to detect infection in most birds. More splenic lesions contained acid-fast organisms than did liver lesions, suggesting that splenic biopsy may have the greatest potential for diagnosis of mycobacterial infection antemortem. Sensitivity was higher for postmortem examination of multiple liver sections than of a single biopsy section; therefore, obtaining multiple liver biopsy sections may increase detection of mycobacteria. Examination of multiple tissues and the use of several different diagnostic techniques significantly increases the probability of diagnosis of mycobacteriosis.

Vaccination against coronaviruses in domestic animals.

The current pandemic of COVID-19 has set off an urgent search for an effective vaccine. This search may well benefit from the experiences of the animal health profession in the development and use of coronavirus vaccines in domestic animal species. These animal vaccines will in no way protect humans against COVID-19 but knowledge of the difficulties encountered in vaccinating animals may help avoid or minimize similar problems arising in humans. Diverse coronaviruses can infect the domestic species from dogs and cats, to cattle and pigs to poultry. Many of these infections are controlled by routine vaccination. Thus, canine coronavirus vaccines are protective in puppies but the disease itself is mild and self-limiting. Feline coronavirus infections may be mild or may result in a lethal immune-mediated disease - feline infectious peritonitis. As a result, vaccination of domestic cats must seek to generate- protective immunity without causing immune-mediated disease. Vaccines against bovine coronavirus are widely employed in cattle where they protect against enteric and respiratory disease in young calves. Two major livestock species suffer from economically significant and severe coronavirus diseases. Thus, pigs may be infected with six different coronaviruses, one of which, porcine epidemic diarrhea, has proven difficult to control despite the development of several innovative vaccines. Porcine epidemic diarrhea virus undergoes frequent genetic changes. Likewise, infectious bronchitis coronavirus causes an economically devastating disease of chickens. It too undergoes frequent genetic shifts and as a result, can only be controlled by extensive and repeated vaccination. Other issues that have been encountered in developing these animal vaccines include a relatively short duration of protective immunity, and a lack of effectiveness of inactivated vaccines. On the other hand, they have been relatively cheap to make and lend themselves to mass vaccination procedures.

Comparison Of Four Anti-Avian IgY Secondary Antibodies Used In Western Blot And Dot-Blot ELISA To Detect Avian Bornavirus Antibodies In Four Different Bird Species.

PURPOSE: This study evaluated the specificity of different avian secondary antibodies used in Western blot and dot-blot ELISA to detect avian bornavirus antibodies in bird plasma. METHODS: Plasma samples were collected from: two Blue and gold macaws, one positive and one negative for avian bornavirus by RT-PCR; a Cockatiel and a Monk parakeet prior to and following experimental infection; and, two Mallards, one positive and one negative for avian bornavirus by RT-PCR Samples were analyzed by Western blot and dot-blot ELISA that incorporated recombinant avian bornavirus nucleoprotein as the target analyte. Four species-specific anti-IgY secondary antibodies were used in the assays: goat anti-macaw IgY, goat anti-bird IgY, goat anti-duck IgY, and rabbit anti-chicken IgY. RESULTS: In the Western blot, anti-macaw IgY secondary antibody produced strong signals with Blue and gold macaw and Cockatiel positive plasma, but no signal with Mallard positive plasma. Anti-bird IgY secondary antibody produced strong signals with Blue and gold macaw, Cockatiel, and Mallard positive plasma. Anti-duck and anti-chicken IgY secondary antibody produced a strong and moderate signal, respectively, only with Mallard positive plasma. In the dot-blot ELISA, there was a distinct and significant difference (P<0.05) in the signal intensity between the different secondary antibodies within a bird species. Anti-macaw IgY secondary antibody produced significantly (P<0.05) stronger signals than the other secondary antibodies in Blue and gold macaw, Cockatiel, and Monk parakeet positive plasma, while anti-duck IgY secondary antibody produced significantly (P<0.05) stronger signals than the other secondary antibodies in Mallard positive plasma. CONCLUSION: In testing psittacines with immunoassays, and especially in assays that incorporate short incubation reaction times such as a dot-blot ELISA, species-specific anti-IgY secondary antibodies provided more accurate results.

Treatment With Nonsteroidal Anti-Inflammatory Drugs Fails To Ameliorate Pathology In Cockatiels Experimentally Infected With Parrot Bornavirus-2.

PURPOSE: Parrot bornavirus is the etiological agent of Parrot bornavirus syndrome, also referred to and comprising proventricular dilatation disease or PDD, macaw wasting disease, enteric ganglioneuritis and encephalitis, and avian ganglioneuritis. It has been suggested that nonsteroidal anti-inflammatory drugs may be able to ameliorate this disease. Therefore, this study investigated the effects of two commonly used nonsteroidal anti-inflammatory drugs, celecoxib and meloxicam, on cockatiels experimentally inoculated with Parrot bornavirus-2 (PaBV-2). MATERIALS AND METHODS: Twenty-seven cockatiels were randomized into 3 groups of 9 birds, matched with respect to historical PaBV shedding, weight, and sex. The cockatiels were inoculated with cell culture-derived PaBV-2 by the intranasal and intramuscular routes. Beginning at 23 days post-inoculation, birds in each group received oral treatment once daily with placebo, meloxicam (1.0 mg/kg), or celecoxib (10.0 mg/kg). RESULTS: Within 33-79 days post-inoculation, 2 birds died and 6 birds were euthanized based on neurological or gastrointestinal signs consistent with Parrot bornavirus syndrome: 2 birds were euthanized in the placebo group, 1 bird died and 1 bird was euthanized in the meloxicam-treated group, and 1 bird died and 3 birds were euthanized in the celecoxib-treated group. Of these 8 birds, black intestinal contents were found upon necropsy in 2 birds of the meloxicam-treated group and 2 birds of the celecoxib-treated group. At day 173 (±2) post-inoculation, the remaining 19 birds were euthanized. Necropsy and histopathology showed lesions characteristic of Parrot bornavirus syndrome in 23 cockatiels. Histopathologic lesions were present in birds of all 3 groups. There was no statistical difference between the groups nor was there a statistical difference among the 3 treatment groups in the detection of PaBV RNA and PaBV nucleoprotein using RT-PCR and immunohistochemistry, respectively. CONCLUSION: Meloxicam and celecoxib treatments do not appear to alter the clinical presentation, viral shedding, gross lesions, histopathology, or viral distribution. Treatment with NSAIDs may cause gastrointestinal toxicity in cockatiels experimentally inoculated with PaBV-2.

Mycobacteriosis in naturally infected ring-neck doves (Streptopelia risoria): investigation of the association between feather colour and susceptibility to infection, disease and lesions type.

Prevalence of infection and disease, the degree of organ involvement and the nature of the lesions were investigated in 11 white and 18 non-white ring-neck doves coming from a flock naturally infected with Mycobacterium avium subsp. avium. Lesions were common in the liver, spleen, lung, kidney, intestines, ovary and bone marrow. Overall, 18 out of 29 (62%) birds were considered infected with a sequevar of M. avium subsp. avium that contains serotypes 2, 3, 4 and 9. The prevalence of infection in the white doves (36.4%) was significantly lower than in the non-white morphs (77.7%). White doves had on average fewer organs affected (mean =3.1) than the non-white doves (mean =5.9). A diffuse pattern of inflammation in the liver and spleen was observed mainly in non-white doves. Focal or multifocal granulomatous inflammation of the liver and spleen was predominant in white doves. Genetic mechanisms of immunity to mycobacteriosis may be contributing or determining these differences. There are three basic colour morphs in ring-neck doves--dark or wild type, blond and white--and the alleles coding for colour are sex-linked and located on the sex (Z) chromosome. Female's single sexual chromosomed (ZW) and homozygous males (ZZ) can be white if they carry the white alleles. It is very probable that the gene or genes modulating the immune response to M. avium subsp. avium infection in these doves could be associated to these loci or at least located in the same (Z) chromosome, as the association with white colour suggests.