Normal Birds Research Articles

Macrorhabdus ornithogaster in ostrich, rhea, canary, zebra finch, free range chicken, turkey, guinea-fowl, columbina pigeon, toucan, chuckar partridge and experimental infection in chicken, japanese quail and mice

Since 2000, Macrorhabdus ornithogaster "megabacteriosis" has been diagnosed in the avian diseases laboratory in a diversity of avian species and varied spectrum of disease. The disease in some species (chickens, turkeys, guinea fowls) was clinically characterized by emaciation, prostration, loss of appetite, cachexia and death, with a typically chronic course. A more acute disease was observed in finches (canary-Serinus and zebra-Taeniopygia) and budgerigars (Melopsittacus undulatus). The large rod shaped organism, visible from 100 times magnification, with and without staining, could be detected in sick and also in reasonably normal individuals of some species, such as chickens, turkeys, quails and pigeons. In rheas (Rhea americana), ostriches (Struthio camelus), canaries, zebra-finches, guinea-fowl (Numida meleagris) and budgerigars. The disease was severe, causing to up to 100% mortality. The infection could be detected in some species along with other infectious or disease problems, such as endoparasites (helminths, coccidia) and ectoparasitism (order Mallophaga or/and order Acarina). The cultivation of M. ornithogaster was successfully achieved in solid and liquid media, originated from chickens (four isolates), guinea fowl (1 isolate), chuckar partridge (1 isolate) and canary (1 isolate). A very interesting finding at microscopy was motility of M. ornithogaster, as detected both in cultures obtained on agar for pathogenic fungi and passaged into thioglycolate broth, as well as on samples observed in wet preparations from in vivo. Differences in colony aspects were noted among the isolates. Experimental infections were attempted in chicken and japanese quail, using a chicken isolate, allowing the detection of the organism in the proventriculus and liver in apparently normal birds. One chicken isolate was injected intraperitoneally in Balb/c mice and resulted in 100% mortality.

Experimental West Nile Virus Infection in Eastern Screech Owls (Megascops asio)

Eastern Screech Owls (EASOs) were experimentally infected with the pathogenic New York 1999 strain of West Nile virus (WNV) by subcutaneous injection or per os. Two of nine subcutaneously inoculated birds died or were euthanatized on 8 or 9 days postinfection (DPI) after <24 hr of lethargy and recumbency. All subcutaneously inoculated birds developed levels of viremia that are likely infectious to mosquitoes, with peak viremia levels ranging from 10(5.0) to 10(9.6) plaque-forming units/ml. Despite the viremia, the remaining seven birds did not display signs of illness. All birds alive beyond 5 DPI seroconverted, although the morbid birds demonstrated significantly lower antibody titers than the clinically normal birds. Cagemates of infected birds did not become infected. One of five orally exposed EASOs became viremic and seroconverted, whereas WNV infection in the remaining four birds was not evident. All infected birds shed virus via the oral and cloacal route. Early during infection, WNV targeted skin, spleen, esophagus, and skeletal muscle. The two morbid owls had myocardial and skeletal muscle necrosis and mild encephalitis and nephritis, whereas some of the clinically healthy birds that were sacrificed on 14 DPI had myocardial arteritis and renal phlebitis. WNV is a significant pathogen of EASOs, causing pathologic lesions with varying clinical outcomes.

Reduction of GABAergic neurons within the tectofugal visual system of white zebra finches

The central visual system of white zebra finches is physiologically and anatomically different from normally coloured (wild type) animals. The main difference to normal birds is an enhanced response to ipsilateral stimulation in all areas of the tectofugal visual pathway. Previous experiments indicated that besides an enhancement of recrossing fibers, it might be a lack of inhibition which causes this effect. We show here that such an explanation can only be true for a part of the entopallium, the telencephalic station of this projection. Only within the so-called perientopallium, the number of GABAergic neurons is strongly reduced, while there is no significant difference between white and wild type birds in the other visual areas. It is speculated that these neurons in normal birds inhibit ipsilateral input conveyed by the second visual projection in birds, the thalamofugal pathway.

The phenol red thread tear test in large Psittaciformes

To develop a standard method for measuring tear production in large Psittaciformes using the phenol red thread (PRT) tear test. To establish mean PRT tear test values in clinically normal pet birds and to assess the reproducibility of the test. Two geographically distinct populations of healthy, large Psittaciformes (pilot study and study population). Species groups include: cockatoo (17), macaw (22), Amazon (10), African gray (1), eclectus (1) and pionus (1). The PRT was placed under the upper eyelid and both eyelids were held closed throughout the test. The PRT tear test was repeated after 2 months in the pilot study and after approximately 5 min in the study population. The mean PRT tear test values for the pilot study were OD=28.2 mm/15 s (+/- 6.3 mm), OS=24.1 mm/15 s (+/- 6.6 mm) and OD=25.4 mm/15 s (+/- 3.3 mm), OS=25.5 mm/15 s (+/- 5.2 mm), for the first and second visits respectively. The mean PRT tear test value for the study population was: OD=19.8 mm/15 s (+/- 4.3 mm), OS=20.1 (+/- 3.9 mm) and OD=20.0 mm/15 s (+/- 4.5 mm), OS=19.1 mm/15 s (+/- 3.3 mm), for the first and second tests respectively. There was poor repeatability between tests. Results suggest that the PRT tear test is a practical method for measuring tear production in large Psittaciformes, although adaptations to the established diagnostic method are necessary to overcome some anatomical differences present in birds. Good reproducibility of the PRT tear test could not be demonstrated in a clinically normal population of birds but geographic location appears to significantly influence results.

Expression of calcineurin and its interacting proteins in epileptic fowl

Calcineurin (CaN), a Ca2+-calmodulin (CaM)-dependent protein phosphatase, is important for Ca2+-mediated signal transduction. The main objective of this study was to examine the potential role of CaN in epileptic brain and its involvement in neuronal apoptosis. We investigated CaN expression and its interaction with various signaling molecules in normal, carrier and epileptic brain tissues of chicken. Our results revealed higher Ca2+-CaM-dependent phosphatase activity of CaN and a correspondingly strong immunoreactive band of CaN A in epileptic and carrier brain samples compared with normal brain. Furthermore, immunohistochemical analysis showed a higher level of expression of CaN in epileptic brain tissue. However, the intensity of immunoreactivity was less in carrier than epileptic brain. We observed that the interaction of CaN with m-calpain and micro-calpain was strong in carrier and epileptic chickens compared with that in normal birds. In addition, the interaction of CaN with Bcl-2, caspase-3 and p53 was greater in carrier and epileptic fowl than in normal chickens. The greater interaction of CaN with various apoptotic factors in epileptic chickens adds to our understanding of the mechanism of CaN signaling in neuronal apoptosis.

Effects of interchanging hyperopic defocus and form deprivation stimuli in normal and optic nerve-sectioned chicks

To test the hypothesis that the same mechanisms mediate form deprivation and lens-induced myopia, the ocular growth responses of chicks alternately exposed to lenses and diffusers at regular intervals (3 h) were compared to those of chicks exposed to either negative lenses or diffusers alone. In total, there were four experiments: (1) −15 D lenses and/or diffusers on normal birds, (2) −15 D lenses and/or diffusers on optic nerve-sectioned (ONS) birds, (3) −5/−10/−15 D lenses (sequentially applied) and/or diffusers on normal birds and (4) −5/−10/−15 D lenses and/or diffusers on ONS birds. All treatments were monocular. In all experiments, optical axial lengths (cornea-to-retina distances) in treated eyes were greater than in fellow eyes, irrespective of the optical device (diffuser, lens or switch), lens power (fixed or incremented) and optic nerve condition (intact or severed). In normal chicks, optical axial length responses in the switch group were significantly reduced relative to those of the diffuser but not to those of the −15 D lens group. For both groups of ONS birds, diffusers exaggerated the optical axial length changes. For all groups, the responses to the switch and lens groups were most similar. These results together suggest that the mechanisms mediating form deprivation- and lens-induced myopia are different.

Silent Synapses in a Thalamo-Cortical Circuit Necessary for Song Learning in Zebra Finches

Developmental changes in synaptic properties may act to limit neural and behavioral plasticity associated with sensitive periods. This study characterized synaptic maturation in a glutamatergic thalamo-cortical pathway that is necessary for vocal learning in songbirds. Lesions of the projection from medial dorsolateral nucleus of the thalamus (DLM) to the cortical nucleus lateral magnocellular nucleus of the anterior nidopallium (LMAN) greatly disrupt song behavior in juvenile birds during early stages of vocal learning. However, such lesions lose the ability to disrupt vocal behavior in normal birds at 60-70 days of age, around the time that selective auditory tuning for each bird's own song (BOS) emerges in LMAN neurons. This pattern has suggested that LMAN is involved in processing song-related information and evaluating the degree to which vocal motor output matches the tutor song to be learned. Analysis of reversed excitatory postsynaptic currents at DLM-->LMAN synapses in in vitro slice preparations revealed a pronounced N-methyl-D-aspartate receptor (NMDAR)-mediated component in both juvenile and adult cells with no developmental decrease in the relative contribution of NMDARs to synaptic transmission. However, the synaptic failure rate at DLM-->LMAN synapses in juvenile males during the sensitive period for song learning was significantly lower at depolarized potentials than at hyperpolarized potentials. In contrast, the failure rate at DLM-->LMAN synapses did not differ at hyper- versus depolarized holding potentials in adult males that had completed the acquisition of a stereotyped song. This pattern indicates that juvenile cells have a higher incidence of silent (NMDAR-only) synapses, which are postsynaptically silent at hyperpolarized potentials due to the voltage-dependent gating of NMDARs. Thus the decreased involvement of the LMAN pathway in vocal behavior is mirrored by a decline in the incidence of silent synapses but not by changes in the relative number of NMDA and AMPA receptors at DLM-->LMAN synapses. These findings suggest that a developmental decrease in silent synapses within LMAN may represent a neural correlate of behavioral plasticity during song learning.

Origin and evolution of highly pathogenic H5N1 avian influenza in Asia

Outbreaks of highly pathogenic avian influenza caused by H5N1 viruses were reported almost simultaneously in eight neighbouring Asian countries between December 2003 and January 2004, with a ninth reporting in...

미역의 급여 수준이 타고난 면역반응이 활성화한 육계병아리의 혈액 항산화 균형에 미치는 영향

Effect of dietary brown seaweed(Undaria pinnatifida) levels on the anti-oxidant enzyme system was evaluated in blood of broiler chicks activated innate immune response. Day-old broiler chicks were fed diets containing 0.0(basal), 1.0, 2.0 and 4.0 % of brown seaweed for 4 weeks. The innate immune response was activated by injecting Salmonella typhymurium lipopolysaccharide(LPS) i.p. at 8, 10 and 12 day of age. The activation of innate immune response enhanced(p< 0.01) and the brown seaweed 1.0 and 2.0 % diets reduced(P< 0.05) the superoxide dismutase(SOD) activity in erythrocyte cytosol significantly. The activation of innate immune response elevated significantly the levels of peroxide and the activity of peroxidase in plasma, while the levels of dietary brown seaweed resulted in a significant linear increase in peroxidase activity in plasma of normal bird. Experience of the innate immune response in 4 week-old chicks reduced linearly the plasma level of peroxide with the level of brown seaweed and enhanced the plasma peroxidase activity. Also, the plasma of normal birds fed the brown seaweed showed higher level of peroxide and lower activity of peroxidase. The results indicated that dietary brown seaweed affected SOD and peroxidase activities in blood of broiler chicks during activation of innate immune response.

Avian malaria: clinical and chemical pathology of Plasmodium gallinaceum in the domesticated fowl Gallus gallus

Data on the effects of Plasmodium gallinaceum on domesticated fowl are sparse, justifying a full investigation of its pathology. Clinical signs following blood-induced infections with the Wellcome line of strain 8A included depression, fever, anorexia, reduced weight gain, poor feed conversion, anaemia, green faeces and often death. After administration of 106 erythrocytic parasites, mortality 5 to 10 days after infection was 10% to 93% in chickens 7 to 84 days old. The older the birds, the lower the mortality and the longer the time to death. Onset of detectable parasitaemia occurred mostly during the second day after infection (59% of birds). Peak parasitaemia (∼70%) occurred on the sixth day in 85% of surviving birds. The patent period was usually 7 to 19 days. Abnormally low haematocrit values of ≤24% and high colonic temperatures of ≥42°C were recorded. A febrile response is demonstrated conclusively here in P. gallinaceum malaria for the first time. Weight gain of malarious birds was reduced by ∼18% to 51%, and feed conversion efficiency was often reduced by ∼12% to 41%. Growth reduction was due entirely to anorexia. Liver weight relative to body weight (normally ∼2% to 3%) increased to ∼4.5% by 8 days, and relative spleen weight (normally ∼0.2%) increased to 1.6% by 12 days. Specific gravities of livers and spleens in healthy and infected birds were ∼1.09. Gall bladder volume in malarious birds 8 days after infection was approximately four times that of normal birds. Statistically significant changes occurred in the proportions of plasma proteins in malarious birds 8 days after infection; albumin and α2-globulin were reduced, while γ1-globulin and γ2-globulin were increased. Those changes coincided with significant increases in concentrations of plasma total protein and the enzymes aspartate aminotransferase, glutamate dehydrogenase and γ-glutamyltransferase, and a decrease in creatinine. Green (biliverdin) colouration of the faeces was a consistent sign of malaria. Birds acquired non-sterile immunity after a single primary infection. The quantitative data presented facilitate selection of the most useful criteria for field diagnosis, estimation of potential economic losses, and assessment of potential avian antimalarial drugs.

Disposition kinetics of doxycycline in chickens naturally infected with Mycoplasma gallisepticum

1. The pharmacokinetic properties of doxycycline were determined in healthy chickens and chickens naturally infected with Mycoplasma gallisepticum after a single intravenous (i.v.) and oral administration of the drug at 20 mg/kg body weight. Tissue residues of the tested drug after an oral dose of 20 mg/kg given twice daily for 5 consecutive days were also estimated in diseased chickens. 2. The plasma concentrations of doxycycline following single i.v. and oral administration were higher in healthy chickens than in diseased ones. Following i.v. injection, the elimination half-life (t 1/2β), distribution half-life and mean residence time (MRT) were longer in healthy chickens than in diseased birds. The values of total body clearance (Cl B) and volume of distribution (V dss) were larger in healthy chickens than in diseased birds. 3. After single oral administration, the absorption half-life (t 1/2ab) and the elimination half-life were longer in normal birds than in diseased ones. The maximum plasma concentration of the drug was higher in normal chickens than in diseased ones. 4. Following repeated oral administration, the concentration of doxycycline in all tissues except muscle was higher than the corresponding concentrations in plasma. Concentrations of doxycycline in different tissues were in the following order: kidney > liver > lung > muscle. The drug was detected in liver and kidney in substantial concentrations on d 5 post administration of the last dose whereas, on d 7, its concentration in all tissues was below the lower limit of the sensitivity of the assay method used. Because of the low sensitivity of the microbiological assay method used in this study, a safe withdrawal time for doxycycline in diseased birds could not be estimated for the meanwhile.

In vivo studies of Gallibacterium anatis infection in chickens

The aim of the present study was to investigate the pathology in normal or immunosuppressed chickens followed intravenous or intraperitoneal inoculation with a well-characterized strain of Gallibacterium anatis. Two groups of 30 15-week-old commercial brown laying chickens were used, having been screened and found negative for Gallibacterium organisms. One group was treated with 5-fluorouracil to promote heterophil depletion, while the other was saline treated. Ten days later 15 chickens from each group were inoculated either intravenously or intraperitoneally with 3.3 x 10(7) colony-forming units of G. anatis strain 12656-12. Subsets of chickens were sacrificed at 3, 12 or 24 h post-infection and examined for lesions. Livers and spleens were examined by culture and by fluorescent in situ hybridization. Intravenously infected birds showed severe septicaemic lesions in both the normal and immunosuppressed birds. Mortality was recorded only in the latter, with an overall rate of 73%. The intraperitoneally infected chickens of normal immune status showed various degrees of localized purulent peritonitis at the inoculation site, but in the immunosuppressed birds the entire peritoneum tended to be involved along with the abdominal organs. This was similar to previous descriptions of natural infections and may represent a useful infection model for detailed analysis of Gallibacterium virulence factors and pathogenesis.

English

RAPD technique was used in this study to detect DNA band variations between both normal and abnormal male of broiler chicken based on RAPD marker. DNA polymorphisms between normal and mutant birds were detected using fifteen oligonucleiotide primers. Using these primers, DNA band loss ranged from 25 to 75%. Data demonstrated that RAPD marker could detect DNA alterations.

A modified biopsy technique to improve histopathological evaluation of avian skin.

Skin biopsies are a viable diagnostic tool in avian dermatology, however, the thinness of avian skin makes it difficult to prevent rolling and contraction of skin biopsy specimens during collection and fixation. The difficulty orienting such rolled samples during processing ultimately interferes with the establishment of a histopathological diagnosis. We describe a modified skin biopsy procedure for obtaining avian skin biopsy specimens. In this technique nontranslucent self-adhesive tape (Scotch tape) was attached to skin biopsy sites before obtaining skin biopsies using a standard skin biopsy punch instrument. A total of 23 skin biopsy specimens were obtained: 15 from nonfeathered skin of 12 normal Hispaniolan parrots, 3 from feathered skin of 2 normal birds and 5 from feathered skin of 3 psittacines presented for pathologic feather-picking. All 23 skin specimens consistently adhered to the tape during the biopsy procedure. The specimens were fixed in 10% neutral phosphate-buffered formalin. During processing, no curling or rolling of specimens occurred, and all specimens could be easily orientated for correct trimming and subsequent histopathological evaluation. The tape technique did not produce any appreciable artefacts. Remnants of the tape were microscopically evident above the stratum corneum assuring that none of the stratum corneum was lost during processing. Obtaining avian skin biopsy specimens using this modified tape technique is easy and ensures flat fixation of the skin biopsy specimens, which later allows trimming at right angles, and through the longitudinal diameter of feather follicles for accurate histopathologic evaluation.

Effect of Perches and Stocking Density on Tibial Dyschondroplasia and Bone Mineralization as Measured by Bone Ash in Broiler Chickens

Exercise through perching has been suggested as a method to reduce the impact of leg problems in broiler chickens. The goal of this research was to determine the effects of stocking density and perch availability on the incidence of tibial dyschondroplasia (TD) and the level of bone ash in broiler chickens. The incidence of TD was lowest in birds raised at the higher densities with 20 and 15 birds/m2 and highest at stocking densities of 10 birds/m2. This pattern was positively correlated with the perching frequency of chickens, as observed at the different experimental densities and reported previously. Except for controls, which had no TD lesions compared to birds with access to perches, TD incidence was lowest in pens with horizontal perches and highest in pens with a combination of horizontal and sloping perches. These differences were not statistically significant. Percentage bone ash was lower in birds with TD than in normal birds (P < 0.05). Bone ash was not affected by stocking density or perch treatment. TD incidence was similar for both sexes; however, percentage bone ash was significantly lower in males than in females (P < 0.02). These results suggest that TD and faster growth rate in males may have a negative impact on bone mineralization in broiler chickens. However, it is unclear from our results whether providing broilers with access to perches can actually improve bone mineralization or prevent TD.

A Geometric Method for Determining Shape of Bird Eggs

Abstract Precise quantification of the oval of a bird egg can provide a powerful tool for the analysis of egg shape for various biological problems. A new approach to the geometry of a bird egg oval is presented here using a simple algebraic equation to fit all normal bird egg shapes. Only two parameters are needed in the equation for complete shape description of an egg oval to quantify the equation's capacity for curve fitting all species and shapes of bird egg ovals. The equation was fitted to egg silhouettes from a sample of 250 different bird egg species containing one egg per species. Standard regression analysis was used to fit the equation to each egg profile. The 99% CI for the curve fit acceptance rate was calculated to determine the equation's statistical significance for all species of bird eggs. Compared to the power series multiequation models (Preston 1968, Todd and Smart 1984), the equation used here is the simplest analytic description of a bird egg oval.

Evaluation of polymerase chain reaction and dot blot hybridisation tests in the diagnosis of pigeon circovirus infections

Polymerase chain reaction (PCR) and dot blot hybridisation (DBH) tests for detecting pigeon circovirus (PiCV) DNA were developed and evaluated using tissue samples obtained from diseased and clinically normal pigeons, which originated in Belgium and Northern Ireland. When PCR product was visually detected, the limit of detection of the PCR test was 31 fg, while that of the DBH was 1.6 pg. For evaluation purposes, the results of the PCR and DBH tests, performed with DNAs extracted from samples of bursa of Fabricius (BF), were compared with those of in situ hybridisation (ISH) and histology. In 32 samples tested by all four tests, 27 (84%) were positive by PCR, 24 (75%) were positive by ISH, 20 (63%) were positive by DBH, and 13 (41%) were positive by histology. Additional PCR testing showed that in some disease-affected birds, PiCV DNA could be detected in a range of tissues including thymus, spleen, liver, kidney and brain. The PCR detection of PiCV DNA in BF samples from clinically normal birds indicated that PCR can detect infections in the absence of disease, a finding that mitigates against its use as a disease diagnostic. In addition, nucleotide sequence determinations indicated that PCR test performance was adversely affected by the sequence diversity exhibited by selected PiCVs. The application of the DBH test to dilutions of test samples indicated that the BF from some diseased pigeons contained very large amounts of virus DNA, as much as 10 13 genome copies/g tissue, and suggested that this test may be a convenient method of providing a semi-quantitative estimate of virus load.

A Geometric Method for Determining Shape of Bird Eggs

Precise quantification of the oval of a bird egg can provide a powerful tool for the analysis of egg shape for various biological problems. A new approach to the geometry of a bird egg oval is presented here using a simple algebraic equation to fit all normal bird egg shapes. Only two parameters are needed in the equation for complete shape description of an egg oval to quantify the equation's capacity for curve fitting all species and shapes of bird egg ovals. The equation was fitted to egg silhouettes from a sample of 250 different bird egg species containing one egg per species. Standard regression analysis was used to fit the equation to each egg profile. The 99% CI for the curve fit acceptance rate was calculated to determine the equation's statistical significance for all species of bird eggs. Compared to the power series multiequation models (Preston 1968, Todd and Smart 1984), the equation used here is the simplest analytic description of a bird egg oval.

Mode of Inheritance of the Low Score Normal Condition in Chickens

The abnormal muscle condition termed low score normal (LSN) was first detected in an outcross of chickens with hereditary muscular dystrophy (MD) to a commercial White Leghorn stock. At 2 to 3 mo of age, normal birds can right themselves between 15 and 20 times (exhaustion score) when placed on their back on a flat surface, whereas birds with MD cannot right themselves under similar conditions. Birds classified as LSN are intermediate to these extremes. The inheritance of the LSN abnormality has not been established.In order to determine if the LSN condition was controlled by a single gene, the LSN line was reciprocally crossed with a White Leghorn line to produce two F1 populations. Two F2 populations were produced by randomly mating individuals within each F1 population. Each F1 population was backcrossed to the White Leghorn line. When birds with an exhaustion score of 6 or less were considered LSN, ratios obtained in the F1 population were 3 normal and 134 LSN individuals for the cross of the LSN line males and White Leghorn line females, and 8 normal and 118 LSN for the reciprocal cross, suggesting that the LSN condition was influenced by a dominant gene with incomplete penetrance. The frequencies did not differ between sexes in either F1 cross, suggesting autosomal inheritance. In general, ratios of normal to LSN individuals in the two F2 populations and in the two backcross populations supported the hypothesis that the LSN trait was controlled by a dominant autosomal gene. However, there was an excess of normal females relative to that expected in the cross of the White Leghorn line males and LSN line females.Heritability (h2) of the LSN trait was estimated by regression of F2 offspring on F1 parents. The h2 estimates based on regressions were higher (range = 0.520 to 1.107) in the LSN line male x White Leghorn line female cross than in the reciprocal cross (range = 0.161 to 0.621). The h2 estimates based on regression of offspring on dams were higher for male offspring than for female offspring, suggesting the presence of sex-linked effects. It was concluded that the LSN trait was influenced primarily by an autosomal dominant gene but was also influenced by other genes, some of which were on the sex chromosome.

Parathyroid hormone-related peptide expression in tibial dyschondroplasia

Parathyroid hormone-related peptide (PTHrP) has a key role in the growth of long bones, as it is a negative regulator of growth plate chondrocyte terminal differentiation. We have examined the distribution and gene expression levels of PTHrP in the growth plates of broiler chickens with tibial dyschondroplasia (TD) in order to determine whether increased expression of PTHrP is responsible for the delayed chondrocyte differentiation that is characteristic of this skeletal disorder. PTHrP protein distribution and gene expression levels were assessed by immunocytochemistry and reverse transcriptase-polymerase chain reaction, respectively. In growth plates of normal birds, PTHrP was found to be distributed throughout all maturational zones of the growth plate. In cartilage proximal to the TD lesion, PTHrP immunostaining and the level of PTHrP gene expression were similar to that observed in normal birds. In contrast, many chondrocytes within the centre of the TD lesion stained poorly for PTHrP and this was reflected in the lower levels of PTHrP mRNA detected in lesion cells. These results suggest that alterations in PTHrP distribution and gene expression are not primarily responsible for the delayed chondrocyte differentiation and hypertrophy noted in dyschondroplasia, but are a result of secondary changes due to the pathology of the condition.