A collagenase gel/physical defect model for controlled induction of superficial digital flexor tendonitis.

REASONS FOR PERFORMING STUDY: A consistent and clinically relevant model for the induction of core lesions confined to the mid-metacarpal superficial digital flexor tendon (SDFT) has not been previously reported. Injection of bacterial collagenase is commonly used but often results in large, irregular and inconsistent lesions that disrupt the superficial tendon layers and epitenon. OBJECTIVE: To develop and evaluate a new injection technique for collagenase induction of SDFT injury. METHODS: Collagenase gel was injected into a physical columnar defect created by longitudinally placing a curved 16 gauge 8.89 cm needle in the mid-metacarpal SDFT in a randomly selected forelimb of 10 horses. A placebo treatment injection was performed 1 week later. Serial ultrasound examinations were performed. Horses were subjected to euthanasia at 2 (n = 2), 4 (n = 2), 8 (n = 4) and 16 (n = 2) weeks post treatment injection. Post mortem magnetic resonance imaging and histological analysis were performed. Gene expression (18S, SCX, TNC, TNMD, COL1A1, COL3A1, COMP, DCN, MMP1, MMP3 and MMP13), total DNA, glycosaminoglycan and collagen content were determined for experimental tendons (n = 10) and unaffected tendons (n = 9). RESULTS: Mid-metacarpal SDFT core lesion induction was successful in all tendons with consistent lesion cross-sectional area and minimal epitenon disruption. Histology confirmed loss of normal tendon architecture after tendonitis induction and subsequent healing of the tendon core lesion. Compared with gene expression in unaffected tendons, several tested genes were significantly upregulated (COL1A1, COL3A1, TNMD, SCX, TNC, MMP13), while others showed significant downregulation (COMP, DCN, and MMP3). CONCLUSION: Compared with the previously used direct injection of collagenase, this injection technique was easily performed and induced more consistent lesions that were mid-metacarpal and did not disrupt the epitenon. POTENTIAL RELEVANCE: This model will allow for objective assessment of therapies for tendon regeneration in the mid-metacarpal SDFT prior to clinical trials and routine clinical application.

Ultrasonography of the equine larynx.

Nasopharyngeal and laryngeal evaluation is important when examining horses with upper airway signs for poor performance. Currently endoscopy is the most common method to evaluate the equine upper airway. Ultrasonography of the equine larynx has not previously been described. Using six cadaveric specimens and four standing horses, the ultrasonographic appearance of the equine larynx was established. A scanning technique, including useful acoustic windows and the normal ultrasonographic appearance at each site, is described. Ultrasound allowed visualization of portions of the hyoid apparatus, laryngeal cartilages, associated soft tissues, and intrinsic and extrinsic laryngeal musculature, that are not seen using endoscopy. Additionally, real-time ultrasound allowed observation of the movement of the vocal folds and the arytenoid cartilages during respiration. In three horses with arytenoid chondritis, ultrasonography aided in the diagnosis and localization of arytenoid abcessation and perilaryngeal inflammation. The establishment of this technique will serve as the basis for future investigations in the evaluation of clinical patients with upper airway abnormalities.

Influence of patient positioning on sensitivity of mesenteric portography for detecting an anomalous portosystemic blood vessel in dogs: 34 cases (1997-2000).

OBJECTIVE: To determine whether sensitivity of detecting an anomalous portosystemic blood vessel during operative mesenteric portography varied with patient positioning. DESIGN: Retrospective study. ANIMALS: 34 dogs with a portosystemic shunt diagnosed via scintigraphy or surgery. PROCEDURE: Portograms were evaluated for a portosystemic blood vessel. Sensitivity was calculated from results obtained with dogs in left lateral, right lateral, and dorsal recumbency and from results obtained with dogs in 2 or 3 positions. Differences in sensitivity among positions and between 2 examiners were evaluated. RESULTS: Sensitivity was 85, 91, and 100% in dorsal, right lateral, and left lateral recumbency, respectively. Sensitivity was lower in dorsal recumbency than in left lateral recumbency, although differences were not significant. There was no significant difference between sensitivity of results obtained in dorsal and right lateral recumbency or right lateral and left lateral recumbency. Sensitivity for combined right lateral and dorsal positions was 97%, which was better than that in dorsal recumbency alone, although the difference was not significant. Because sensitivity in left lateral recumbency was 100%, there was no need to evaluate the improvement obtained by combining the result of this position with the results of other positions. CONCLUSION AND CLINICAL RELEVANCE: Results of mesenteric portography varied with patient positioning. The optimal position varied among patients but left lateral recumbency may be better and dorsal recumbency worse. Sensitivity may be improved by performing the test with the patient in orthogonal recumbent positions.

The clinical and metabolic effects of rapid weight loss in obese pet cats and the influence of supplemental oral L-carnitine.

The efficacy, safety, and metabolic consequences of rapid weight loss in privately owned obese cats by means of a canned weight-reduction diet and the influence of orally administered L-carnitine on rate of weight loss, routine clinical evaluations, hepatic ultrasonography, plasma amino acid profiles, and carnitine analytes were evaluated. A double-blinded placebo-controlled design was used with cats randomly divided into 2 groups: Group 1 (n = 14) received L-carnitine (250 mg PO q24h) in aqueous solution and group 2 (n = 10) received an identical-appearing water placebo. Median obesity (body condition scores and percentage ideal body weight) in each group was 25%. Caloric intake was restricted to 60% of maintenance energy requirements (60 kcal/kg) for targeted ideal weight. The reducing formula was readily accepted by all cats. Significant weight loss was achieved by week 18 in each group without adverse effects (group 1 = 23.7%, group 2 = 19.6%). Cats receiving carnitine lost weight at a significantly faster rate (P < .05). Significant increases in carnitine values developed in each group (P < .02). However, significantly higher concentrations of all carnitine moieties and a greater percentage of acetylcarnitine developed in cats of group 1 (P < .01). The dietary formula and described reducing strategy can safely achieve a 20% weight reduction within 18 weeks in obese cats. An aqueous solution of L-carnitine (250 mg PO q12h) was at least partially absorbed, was nontoxic, and significantly increased plasma carnitine analyte concentrations as well as rate of weight loss.

Serum-effusion albumin gradient in dogs with transudative abdominal effusion.

A prospective clinical study in dogs with transudative abdominal effusions examined the clinical usefulness of the serum albumin-effusion albumin (SA-EA) gradient. In humans, the SA-EA gradient facilitates classification of abdominal effusion, with a gradient > or = 1.1 indicating the presence of portal hypertension. Gradient values proved useful for predicting therapeutic response to sodium restriction and diuresis in humans. Of 49 dogs evaluated, 25 had hepatobiliary disease (group 1) and 24 had other nonhepatobiliary conditions (group 2). Portal hypertension was clinically suspected in 24 of 25 dogs in group 1 and in 15 of 24 dogs in group 2. A broad range of SA-EA gradients was found. A gradient > or = 1.1 was found in 22 of 25 (88.0%) dogs with liver disease and in 14 of 24 (58.3%) dogs with other disorders. The median SA-EA gradient was higher in group 1 than in group 2, with values of 1.4 (range, 0.7-3.1) and 1.1 (range, 0.3-2.6), respectively (P < .04). Considerable overlapping of SA-EA gradients occurred between groups and among dogs with diverse conditions such that gradient values could not distinguish dogs with hepatobiliary disease from dogs with other conditions. The overall diagnostic accuracy of the SA-EA gradient in predicting portal hypertension in dogs with and without hepatobiliary disease (69.4%) exceeded that of hypoalbuminemia (57.1%). These findings suggest that portal hypertension is a predominant force in formation of transudative abdominal effusion in dogs with hepatobiliary disease and in dogs with other disorders. Whether the SA-EA gradient can be used to guide therapeutic mobilization of effusion in dogs remains to be proved.

Pulmonary lymphomatoid granulomatosis in a cat.

Pulmonary lymphomatoid granulomatosis was diagnosed in a 9-year-old castrated male domestic shorthair cat with a history of coughing, lethargy, and anorexia. Radiographic examination revealed multiple pulmonary opacities, consolidation of left lung lobes, and enlarged tracheobronchial lymph nodes. Cytologic examination of impression smears of abnormal pulmonary tissue revealed erythrocytes, lymphocytes, and macrophages, with scattered atypical lymphocytes and binucleate cells. Histopathologic evaluation of abnormal lung tissue revealed multiple, coalescing, densely cellular nodules composed of anaplastic and pleomorphic lymphocytes, with scattered binucleate and multinucleate cells. Marked infiltration and effacement of bronchiolar and vascular smooth muscle were present. These features are characteristic of lymphomatoid granulomatosis. To the authors' knowledge, this is the first report of pulmonary lymphomatoid granulomatosis in a cat.

Glomerular filtration rate and renal volume in dogs with congenital portosystemic vascular anomalies before and after surgical ligation.

Glomerular filtration rate (GFR) and renal volume were evaluated in dogs with confirmed portosystemic vascular anomalies (PSVA) before and after surgical ligation of their PSVA. Pre- and postligation CBC, serum biochemistry, urinalysis, abdominal ultrasonography with measurement of renal volume, and per rectal scintigraphy were performed to document resolution of abnormalities consistent with portosystemic shunting. GFR was estimated by plasma 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA) clearance before (n = 21) and after (n = 12) surgical correction of PSVA. Preligation 99mTc-DTPA GFR was increased (median, 5.64 mL/minute/kg; range, 3.53-8.49 mL/minute/kg; reference range, 2.83-4.47 mL/minute/kg) in 81% (17/21) of dogs. Postligation 99mTc-DTPA GFR decreased in all 12 evaluated dogs (median change = -42%; P < .001). Preligation renal volume was above the reference range for the left and right kidneys in 71% (10/14) and 69% (11/16) of dogs evaluated, respectively. Right renal volume decreased significantly (n = 5; median change, -45%; P = .03) after surgical ligation of PSVA. These findings document increased GFR and renal volume in dogs with PSVA, which may explain in part the low blood urea nitrogen and serum creatinine concentrations encountered in these dogs. Knowledge of changes in GFR associated with PSVA ligation may prove helpful in the anesthetic, drug, and dietary management of affected dogs.

Antiviral activity and toxicity of fialuridine in the woodchuck model of hepatitis B virus infection.

Woodchucks were used to study the antiviral activity and toxicity of fialuridine (FIAU; 1,-2'deoxy-2'fluoro-1-beta-D-arabinofuranosyl-5-iodo-uracil). In an initial experiment, groups of six chronic woodchuck hepatitis virus (WHV) carrier woodchucks received daily doses of FIAU by intraperitoneal injection for 4 weeks. At 0.3 mg/kg/d, the antiviral effect was equivocal, but at 1.5 mg/kg/d, FIAU had significant antiviral activity. No evidence of drug toxicity was observed during the 4-week period of treatment or during posttreatment follow-up. In a second experiment, groups of nine WHV carriers or uninfected woodchucks were given 1.5 mg/kg/d of FIAU orally for 12 weeks, and the results compared with placebo-treated controls. After 4 weeks, the serum WHV-DNA concentration in the FIAU-treated carrier group was two to three logs lower than that in the placebo-treated group. After 12 weeks of FIAU treatment, serum WHV DNA was not detectable by conventional dot-blot analysis, hepatic WHV-DNA replicative intermediates (RI) had decreased 100-fold, and hepatic expression of WHV core antigen was remarkably decreased. No evidence of toxicity was observed after 4 weeks, but, after 6 to 7 weeks, food intake decreased and, after 8 weeks, the mean body weights of woodchucks treated with FIAU were significantly lower than controls. Anorexia, weight loss, muscle wasting, and lethargy became progressively severe, and all FIAU-treated woodchucks died or were euthanized 78 to 111 days after treatment began. Hepatic insufficiency (hyperbilirubinemia, decreased serum fibrinogen, elevated prothrombin time), lactic acidosis, and hepatic steatosis were characteristic findings in the final stages of FIAU toxicity in woodchucks. The syndrome of delayed toxicity in woodchucks was similar to that observed previously in humans treated with FIAU, suggesting that the woodchuck should be valuable in future investigations of the molecular mechanisms of FIAU toxicity in vivo and for preclinical toxicological evaluation of other nucleoside analogs before use in patients.

A syndrome resembling idiopathic noncirrhotic portal hypertension in 4 young Doberman pinschers.

We describe 4 young male Doberman Pinschers (3 littermates and 1 unrelated dog) with a syndrome resembling idiopathic or noncirrhotic portal hypertension of humans. Each dog was evaluated for a hepatopathy resulting in portal hypertension, development of portosystemic collateral vessels, and hepatic encephalopathy. These dogs differ from previous reports of young dogs with hepatic insufficiency associated with portal hypertension and acquired portal systemic shunting by their lack of intrahepatic arteriovenous fistulae, portal vein atresia, or intrahepatic fibrosis. Clinicopathologic features included erythrocyte microcytosis, normal to mildly increased liver enzyme activities, increased concentrations of serum bile acids, reduced plasma indocyanine green clearance, and normal total bilirubin concentration. Abdominal ultrasonography disclosed a small liver and portosystemic collateral vessels. Radiographic imaging studies confirmed hepatofugal portal circulation and discounted hepatic arteriovenous fistulae. Histopathologic features in liver tissue from each dog were similar and consistent in all sections examined. Common findings included increased cross-sectional views of hepatic arterioles; hepatic lobular atrophy; scanty increase in connective tissue around some large portal triads; and absence of inflammation, disturbed lobular architecture, bile duct proliferation, or intrahepatic cholestasis.

Suspected microscopic hepatic arteriovenous fistulae in a young dog.

Portal hypertension can develop from any disorder that obstructs portal blood flow and may cause ascites in young dogs. Anomalous hepatic arteriovenous (AV) connections are rare but should be suspected in any young dog with portal hypertension or ascites. All previous reports of dogs with hepatic AV fistulae have documented macroscopic connections between the arterial and venous systems. Identical clinical signs and histopathologic findings can develop in dogs in which a macroscopic hepatic AV connection cannot be detected. Microscopic AV connections may be responsible for clinical signs in these dogs.

Effects of oral ursodeoxycholic acid in healthy cats on clinicopathological parameters, serum bile acids and light microscopic and ultrastructural features of the liver.

A blind, placebo-controlled study evaluated the effects of ursodeoxycholic acid (UDCA) given orally, at a dose of 15 mg kg-1 per day for eight weeks, on the physical condition, haematological and serum biochemical profiles, urinalysis, total serum bile acids (TSBA) and hepatic histology of four healthy cats. There were no clinically important significant differences between the groups or within the treatment groups in clinicopathological parameters. TSBA concentrations or histology. A significant lower concentration/proportion of taurochenodeoxycholic acid was observed in the treated cats (P = 0.05). Only one treated cat accumulated measurable quantities of UDCA, and the compound appeared to be non-toxic. It did not increase the concentration of TSBA, and accumulated minimally in the serum. It should be investigated for therapeutic use in cats with hepatobiliary disease.

Characterization of hepatoportal microvascular dysplasia in a kindred of cairn terriers.

Hepatoportal microvascular dysplasia (MVD), a congenital disorder of the hepatic vasculature, is described in a kindred of Cairn Terrier dogs. Cairn Terrier dogs (n = 165) were evaluated using the serum bile acid test. Affected dogs, identified by abnormal fasting or postprandial serum bile acid concentrations, were divided into 2 groups. Group 1 dogs (n = 147) were used for pedigree analysis. Group 2 dogs (n = 18) were characterized on the basis of history, physical examination, clinicopathologic studies, diagnostic imaging of the liver and portal circulation, and hepatic histopathology. Group 2 contained control dogs (n = 2), dogs with hepatoportal MVD (n = 11), and dogs with macroscopic portosystemic vascular anomalies (PVSA) (n = 5). With the exception of high serum bile acid concentrations, dogs with hepatoportal MVD were indistinguishable from control dogs on the basis of history, physical examination, clinicopathologic findings, survey abdominal radiography, abdominal ultrasound, or transcolonic scintigraphy. Contrast portography in dogs with MVD revealed abnormalities of terminal twigs of the portal vasculature with out large intrahepatic or extrahepatic shunting vessels. Histopathologic abnormalities in dogs with hepatoportal MVD were similar to those reported for dogs with PSVA. Pedigree analysis suggested an autosomal inheritance for MVD. Dogs with MVD had high serum bile acid concentrations, abnormal indocyanine green clearance, and hepatic pathology suggestive of PSVA, but they lacked characteristic clinical findings of PSVA. The clinical significance of MVD is unclear. Dogs with MVD were clinically normal when evaluated but long-term follow-up is not yet available. Dogs with hepatoportal MVD should be identified at an early age to avoid confusion in future diagnostic evaluations.

Scintigraphy for diagnosis of avulsions of the origin of the suspensory ligament in horses: 51 cases (1980-1993).

The medical records of 34 horses with a diagnosis of avulsion of the origin of the suspensory ligament that had been admitted to the veterinary medical teaching hospital between 1980 and 1993 were identified. In addition to clinical examination, 21 of 34 horses had scintigraphy and radiography performed during their examination. The usefulness of scintigraphy and radiography were assessed by comparing the initial findings reported in the medical record to those obtained in a retrospective review of the images. Thirty other horses with scintigraphic lesions of the proximal aspect of the third metacarpal/metatarsal bone but with a confirmed diagnosis other than avulsion of the suspensory ligament served as controls for lesion specificity. Scintigraphy (bone phase, n = 21) revealed increased uptake in all horses in both reviews. Only 14 of 21 (67%) horses radiographed, however, had at least 1 lesion during the initial radiographic evaluation that was reported to be suggestive of avulsion. When the radiographs were reviewed retrospectively, the radiologist identified 18 of 21 (86%) horses with lesions consistent with avulsion. The interpretation of scintigraphy appeared to be a more repeatable and sensitive diagnostic method than radiography. However, though scintigraphy was sensitive in identifying inflammation of the proximal aspect of the metacarpal/metatarsal region, no specific diagnosis of avulsion could be made without coincident radiography; the specificity of scintigraphy in diagnosing avulsion of the suspensory ligament was only 41% (21/51).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of exercise and polysulfated glycosaminoglycan on the development of osteoarthritis in equine carpal joints with osteochondral defects.

This study assessed the effects of postoperative exercise and intra-articular polysulfated glycosaminoglycan (PSGAG) on the repair of osteochondral defects in the carpal joints of ponies. Eighteen ponies with normal carpi had osteochondral defects (mean dimensions 2.4 cm x 0.9 cm) created arthroscopically on the dorsal aspect of the distal articular surface of the radial carpal bone. The ponies were randomized (while balancing for age [range, 2 to 15 years; median, 5.0 years]) to two groups--nine ponies were exercised and nine were stall confined. Beginning at surgery, six ponies in each group received five weekly intra-articular injections of PSGAG (250 mg) in one joint and lactated Ringer's solution in the contralateral joint; the remaining three ponies in each group received lactated Ringer's solution in both joints. The incremental exercise schedule on a circular, rotating walker was begun six days after surgery and occurred twice daily, reaching a maximum of 0.7 miles of walking and 2.7 miles of trotting by the third postoperative month. The effects of treatment on the joint tissues were determined by weekly lameness examinations and measurement of the range of carpal joint motion, carpal radiographs at six and 17 weeks after surgery, synovial fluid analysis, and cytologic evaluation of alcohol-fixed synovial fluid specimens at weeks 1 through 4 and week 17, and histology of the synovial membrane. Ultrasound images of the carpi were acquired before operation and at weeks 1, 2, 4, 8, 10, 13, and 17. Ponies were euthanatized 17 weeks after surgery. Exercise, without medication, caused more lameness throughout the study compared with no exercise. Exercised, nonmedicated ponies had the greatest limitation to carpal flexion (more painful joints), and nonexercised, nonmedicated (control) ponies had the least limitation to flexion. Radiographic scores indicated that the exercised, nonmedicated ponies had significantly (p < .05) more signs of osteoarthritis than exercised, medicated and control ponies. Ultrasonographic measurements indicated that exercise, without medication, caused the greatest increase in combined measurement of the joint capsule thickness and synovial fluid accumulation at all postoperative times. Synovial lining cell numbers in the synovial fluid from exercised ponies were significantly (p < .05) higher than in nonexercised ponies at week 1, and this trend continued at weeks 4 and 17 (p < .1). There were significantly (p < .05) more morphologic abnormalities in the synovial lining cells from exercised than from nonexercised ponies at week 17. Medication with PSGAG enabled exercised carpal joints to be flexed significantly further from weeks 2 through 6 compared with nonmedicated joints.(ABSTRACT TRUNCATED AT 400 WORDS)

Keratan sulfate as a marker of articular cartilage catabolism and joint treatment in ponies.

Keratan sulfate (KS) is a glycosaminoglycan, distribution of which is confined mostly to hyaline cartilage. As such, it is a putative marker of hyaline cartilage catabolism. In experiment 1, a focal osteochondral defect was made arthroscopically in 1 radial carpal bone of 2 ponies, and in 2 other ponies, chymopapain was injected into the radiocarpal joint to induce cartilage catabolism. Sequential and concurrent plasma and synovial fluid concentrations of KS were measured, up to 13 months after induction of cartilage injury, to determine whether changes in KS concentrations reflected cartilage catabolism. In experiment 2, a large, bilateral osteochondral defect was made in the radial carpal bones of 18 ponies, which were subsequently given postoperative exercise and/or injected intra-articularly with 250 mg of polysulfated glycosaminoglycan (PSGAG). Medication was given at surgery, then weekly for 4 weeks. Blood samples were collected and synovial fluid was aspirated before surgery, when medication was given, and at postmortem examination (postoperative week 17). The KS concentration was measured in these fluids to determine whether changes in KS concentration indicated an effect of joint treatment. In experiment 1, the concentration of KS in synovial fluid was highest 1 day after joint injury, and the concentration in plasma peaked 2 days after joint injury. For ponies receiving chymopapain intra-articularly (generalized cartilage catabolism), a fivefold increase over baseline was observed in the concentration of KS in plasma (peak mean, 1.2 micrograms/ml), and a tenfold increase over baseline in synovial fluid (peak mean, 2.0 mg/ml) was observed. On average, these maxima were threefold higher than values in fluids of ponies with osteochondral defects (focal cartilage disease). In experiment 2, nonexercised ponies had lower KS concentration (as a percentage of the preoperative concentration) in synovial fluid than did exercised ponies at all postoperative times, and at postoperative week 17, this effect was significant (P < 0.05). This may be related to decreased turnover of KS in articular cartilage attributable to stall confinement and late increase in turnover related to exercise. Seventeen weeks after surgery, synovial fluid from exercised, medicated ponies had significantly (P < 0.05) higher KS content than did fluid from exercised, nomedicated ponies. This indicated that exercise, when combined with medication, may increase KS release from articular cartilage. Synovial fluid from medicated joints of nonexercised ponies had significantly (P < 0.05) lower KS concentration than did synovial fluid from nonmedicated joints of nonexercised ponies.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral adrenalectomy as a treatment for adrenocortical tumors in ferrets: five cases (1990-1992).

Adrenocortical tumors were diagnosed in 5 adult spayed ferrets. Four ferrets had bilaterally symmetrical alopecia of the caudal femoral region, abdomen, and tail, and 1 had alopecia of the distal limbs and feet. All 5 ferrets had vulvar swelling. During abdominal ultrasonography, irregular masses, believed to involve the adrenal glands, were seen in all 5 ferrets. Unilateral adrenalectomy was performed successfully in each ferret by use of ventral midline celiotomy. On histologic examination of biopsy samples, 4 ferrets were found to have adrenocortical adenomas, and 1 ferret was found to have an adrenocortical adenocarcinoma. All clinical signs resolved after adrenalectomy, suggesting that the adrenocortical tumors had been secreting adrenocortical hormones.

Detection of retrovirus sequences in budgerigars with tumours.

Renal tumours are a common neoplastic disease of budgerigars. Although a retro-virus has been implicated as the aetiological agent, there is no definitive proof for this hypothesis. Sixteen birds suspected to have renal tumours were examined in an attempt to elucidate the possible role of retroviruses. Thirteen birds had renal tumours and the majority of these birds showed abdominal enlargement and paresis. Renal masses were detected by radiography in nine birds. Post-mortem examination confirmed the presence of abdominal tumours which were mostly confined to the kidneys. All of the renal tumours were carcinomas. ELISA tests to detect the presence of p27 of avian leukosis virus and virus isolation attempts were negative. DNA from eight tumours was examined by dot-blot hybridization for the presence of sequences hybridizing with a full length clone of the RAV-2 strain of the avian leukosis virus. A positive reaction was detected with DNA from 6/8 tumours. Southern blot hybridization demonstrated the presence of a 7.2 kb fragment following restriction with BamHI and a 4.6 kb fragment in an additional tumour following digestion with EcoRI that were recognized by the RAV-2 probe. These results suggest the presence of a retrovirus in tumours of budgerigars.