Legislative Differences Governing Exotic Animal Practice.

Laws regulating exotic animal ownership vary throughout the world. While some differences regarding the legal status and use of exotic companion animals are associated with cultural differences and public perception, some differences may result in different outcome, which could be of interest for other parts of the world. This article provides a general overview of relevant laws pertaining to exotic companion animals in certain developed countries.

OCCURRENCE OF GERM CELL NEOPLASIA IN MALE STRIPED BASS (MORONE SAXATILIS) UNDER HUMAN CARE IN A PUBLIC AQUARIUM: SURGICAL TREATMENT AND OUTCOME.

The striped bass (Morone saxatilis) has been a fish species of special concern in Canada since its marked decline in the early 21st century in the St. Lawrence River. Individuals kept in public aquaria contribute to public education and could support conservation efforts through research. Over a 3-yr period, 12 male striped bass housed in a multispecies exhibit developed coelomic distension. The testes were enlarged (12/12), cystic (2/12), and heterogeneous (3/12) on coelomic ultrasound. Upon coeliotomy, enlarged (12/12), partially (4/12) or totally white discolored (6/12) testes were noted. These were associated with coelomic hemorrhage (8/12), effusion (3/12) or adhesions to surrounding organs (9/12). Orchiectomies were performed in all fish. Among these, seven fish survived 2 mon postsurgery, and four fish were still alive 900 d postsurgery. Germ cell neoplasia was diagnosed on histopathological examination in 9 of 12 individuals, but no abnormalities were found in the three other cases. Preventive orchiectomies were performed on the remaining six male striped bass in this exhibit. Germ cell neoplasms were present in two of these six fish. No anesthetic or surgical complications were noted; all six cases were alive 2 mon postsurgery and four of the fish survived 900 d postsurgery. Survival times were not significantly different between fish that underwent preventive or curative orchiectomy (P = 0.19). Although risk factors associated with the development of these gonadal tumors remain unknown, a genetic or environmental origin is suspected. Orchiectomy should be considered in suspected cases of testicular tumors.

Early decrease of ionized calcium and static symmetric dimethylarginine concentration in a model of renal tubular necrosis in corn snakes (Pantherophis guttatus).

OBJECTIVE: To determine if plasma concentrations of symmetric dimethylarginine (SDMA), N-acetyl-beta-d-glucosaminidase (NAG), GGT, ALT, AST, lactate, total calcium, and ionized calcium (iCa) and the calcium:phosphorus ratio are clinically relevant biomarkers to detect early stages of tubular lesions in snakes. ANIMALS: 6 adult corn snakes (Pantherophis guttatus). METHODS: Corn snakes were administered 11 injections of gentamicin at 50 mg/kg, SC, q 24 h in an experimental model of induced tubular necrosis. Plasma biochemistry and blood gas analyses were performed at baseline and after the 3rd and 11th injections. Parameters were compared between time points using a paired Wilcoxon test. In 3 individuals, renal biopsies were collected at baseline before starting injections and at the 3rd and 11th injections, while renal tissue samples were procured after euthanasia in all individuals. RESULTS: Renal proximal and distal tubular necrosis and hepatic steatosis were present in all individuals at necropsy. Compared to baseline, decreased blood concentrations of lactate, ionized calcium, and total calcium and a decreased calcium:phosphorus ratio were noted. A significant decrease of lactate and ionized calcium was observed after 3 days. Conversely, no changes in SDMA, NAG, ALT, AST, GGT, and sodium were detected. CLINICAL RELEVANCE: Ionized calcium and lactate concentrations were the earliest parameters to decrease compared to baseline values in this experimental model. While SDMA is a sensitive indicator of renal disease in mammals, this biomarker did not increase in a model of induced acute tubular necrosis in corn snakes.

A Post-Operative Follow-Up of an Endangered Saltwater Fish Lensectomy for Cataract Management in a Public Aquarium: A Case Series.

Mature cataracts can be a life-threatening condition in fish as it may result in anorexia. Lens extraction has been previously described in fish, but the long-term outcome of this procedure has not been evaluated. Eleven captive-bred adult fish housed in a public aquarium presented with unilateral (n = 3/11) or bilateral (n = 8/11) mature cataracts. All cases belonged to three endangered fish populations: striped bass (Morone saxatilis) originating from the Saint Lawrence River and Atlantic and spotted wolffish (Anarhichas lupus and Anarhichas minor). Pre-operatively, fish presented with anorexia, dark discoloration, abnormal position in the water column, skin abrasions, and/or decreased body condition scores. A lensectomy was performed in eleven fish, including a bilateral procedure in four fish, corresponding to fifteen eyes. Follow-up examinations were performed one to two weeks and one year post surgery. The main complication was self-resolving: corneal edema was present in 67% of eyes, persistent after a week in 47% of eyes, and resolved thereafter. Post-operatively, 73% of fish resumed feeding and regained a good body condition score. Persistent visual impairment post-surgery associated with anorexia required euthanasia in three out of eleven cases. The median time of death was 336 days post surgery (range: 27-1439 days) and three cases were still alive 1334 to 1425 days after the lensectomy. This was considered a favorable outcome for these older individuals with concurrent diseases.

Determination of Coagulation Parameters by Whole Blood Dynamic Viscoelastic Coagulometry in Strigiformes.

No reference values are available in Strigiformes to evaluate blood coagulation using dynamic viscoelastic coagulometry (DVC) with the Sonoclot (Sienco, Boulder, CO, USA) analyzer. The objectives of this study were 1) to assess the feasibility of DVC in Strigiformes, 2) to calculate the index of individuality of each coagulation parameter, and 3) to assess interspecies variability and establish reference intervals, if relevant, based on the index of individuality. Fresh whole blood samples were obtained from healthy Strigiformes, including 13 barred owls (Strix varia), 10 great horned owls (Bubo virginianus), 6 snowy owls (Bubo scandiacus), and 7 eastern screech owls (Megascops asio), and analyzed with DVC with glass bead (gb) and kaolin clay (k) coagulation activators. Activated clotting time (ACT), clot rate (CR), and platelet function were determined immediately after collection using fresh native whole blood. Intraindividual variability was assessed with a second fresh native whole blood sample from 5 barred owls. Interindividual variability was assessed using a Kruskall-Wallis test. For the parameters gbACT (n = 35), gbCR (n = 34), and kACT (n = 27), no significant differences were detected between species (all P ≥ 0.05). Based on low index of individuality, global Strigiformes reference intervals were determined for gbACT (32.3-852.5 seconds; n = 35), gbCR (0-20.1 units/min; n = 29), and kACT (0-1570.3 seconds; n = 27). In conclusion, DVC can be used in Strigiformes and the gb coagulation activator would be more appropriate when basal individual values are not available in a tested individual.

MANAGEMENT OF SUSPECTED DILATED CARDIOMYOPATHY WITH PIMOBENDAN IN TWO LEOPARD SHARKS (TRIAKIS SEMIFASCIATA).

Two adult male leopard sharks (Triakis semifasciata) under managed care were diagnosed with suspected dilated cardiomyopathy. Clinical signs included lethargy, inappetence, and regurgitation. On cardiac ultrasound, fractional shortening was 14% and 10%, respectively (versus 21%-31% in four healthy conspecifics). Ventricular end-diastolic diameter to body weight ratio was 1.72 cm/kg in Case 1 (versus 0.52-1.24 cm/kg in four conspecifics). These results collectively suggested a dilated cardiomyopathy. Treatment was implemented with oral pimobendan at 0.3 mg/kg q48h for 1 mon. The pimobendan dose was increased to 0.5 mg/kg 3/wk, following plasmatic dosage of pimobendan and its metabolite. After 3 mon, fractional shortening increased to 38% and 20%, respectively, sharks regained a normal appetite, and body weight increased by 50% in one individual. After 2 yr, both individuals remained clinically normal, and no adverse effect was noted with pimobendan administration. Pimobendan plasma concentration suggested that this medication was well absorbed in this species.

SEROLOGIC RESPONSE AND ADVERSE EFFECTS OF RECOMBINANT CANINE DISTEMPER VACCINATION IN THREE AQUARIUM-HOUSED WALRUSES (ODOBENUS ROSMARUS).

Fatalities have been associated with phocine and canine distemper viruses in marine mammals, including pinnipeds. No data are available regarding distemper disease or vaccination in walruses. This study evaluates seroconversion and clinical adverse effects following administration of a canarypox-vectored recombinant distemper vaccination (two 1-ml doses, 3 wk apart) in three adult aquarium-housed walruses. Serum antibodies to distemper were measured using seroneutralization on blood samples collected under operant conditioning prior to and for 12 mon after vaccination or until titers were <32. All walruses seroconverted. Medium positive titers (64-128) were detected for 4 to 9.5 mon in two of three individuals. Interindividual variability was noted, with one individual displaying only low positive titers. Major swelling at the site of injection and lameness for a week following injection occurred in all three walruses. Further studies on dosing amount and interval are needed to make vaccine recommendations in this species.

Establishment of preliminary reference intervals and cytochemical staining of blood cells in big-bellied seahorses (Hippocampus abdominalis).

BACKGROUND: Despite their popularity, hematology reference intervals (RIs) have not been established in big-bellied seahorses (Hippocampus abdominalis). OBJECTIVE: The objectives of this study were to establish hematologic RIs to compare values between sex in regard to cytochemical staining of blood cells. We also sought to compare white blood cell concentrations using the Natt and Herrick technique vs blood smear estimates. METHODS: Forty-three healthy individuals from the Aquarium du Québec (22 females and 21 males) were included. Normal health status was confirmed by an unremarkable physical examination in five individuals and by necropsy of five other individuals, of which all were excluded from further analyses. Venipuncture was performed from the ventral coccygeal vein in the remaining 33 individuals without anesthesia using heparinized insulin syringes. A blood volume of 0.05 to 0.1 ml was collected to prepare Wright Giemsa-stained blood smears and hematocrits immediately after venipuncture. Whole blood was stored in heparinized Eppendorf tubes to determine red and white blood cell concentrations using the Natt and Herrick technique with a hemocytometer in 10 individuals; these results were compared with blood smear estimates. Additional blood smears were stained with alkaline phosphatase substrate, periodic acid Schiff, and toluidine blue stains. RESULTS: The reference intervals included the packed cell volume (27.4-67.5%), thrombocyte count (19.5-197.7 × 109 /L), and white blood cell (WBC) count (2-54.8 × 109 /L), including neutrophils (1.1-21.3 × 109 /L), lymphocytes (2.7-45.5 × 109 /L), and monocytes (0-2.2 × 109 /L). The WBC hemocytometer counts showed no correlation with blood smear estimates (Spearman's rho = 0.2). There was also no significant difference between the sexes. CONCLUSIONS: These preliminary reference intervals will help assess the health of seahorses.

Risk Factors and Prognosis for Humeral Fractures in Birds of Prey: A Retrospective Study of 461 Cases from 2000 to 2015.

The objectives of this retrospective study were 1) to characterize humeral fractures in raptors at a rehabilitation program, 2) to determine risk factors for closed and compound humeral fractures in the raptors, and 3) to investigate prognostic factors for humeral fractures in raptors. Of the 6017 birds of prey admitted over 15 years to the Université de Montréal raptor rehabilitation program, 461 birds presented with a humeral fracture. The highest occurrences of humeral fractures were documented in short-eared owls (33%; Asio flammeus), Northern hawk-owls (24%; Surnia ulula), long-eared owls (20%; Asio otus), and Northern harriers (19%; Circus hudsonius). Humeral fractures were more common in males, and species from the intermediate weight group (300 g to 1 kg) were more likely to have compound humeral fractures than birds from the lower and higher weight groups. Humeral fractures of the middle and distal third of the bone were diagnosed as compound more often than fractures of the proximal third. A correlation between the occurrences of humeral fractures and the relative average width of the humerus for each species was observed and suggests that species with slender humeri have an increased likelihood of compound humeral fractures. Following the triage criteria used at this rehabilitation program, surgical (119 birds) or nonsurgical (77 birds) treatments were attempted. Release rate for birds without concomitant conditions in which a treatment was attempted was 39.3% (59/150) and did not significantly differ between closed and compound fractures, which suggests that the triage criteria used for compound fractures in this program were adequate. Our findings emphasize that raptors should not be systematically euthanatized when presented with compound humeral fractures to a rehabilitation facility.

Outcomes of Birds of Prey with Surgical or Traumatic Wing Amputation: A Retrospective Study from 1995 to 2017.

Surgical amputation of a limb is often required to treat raptor orthopedic injuries at rehabilitation centers. In some cases, amputation is an alternative to euthanasia if the bird's welfare is deemed appropriate under human care. The outcome for raptors maintained in a captive setting following wing amputation is poorly documented. A retrospective study was conducted in a Canadian raptor rehabilitation facility to assess the outcomes and complications observed in captive and free-living raptors with partial or complete, surgical or traumatic amputations of the wing. Data from raptors admitted to the rehabilitation center from 1995 to 2017 were reviewed. Overall, 32 records were included in this retrospective study from 11 species of raptors with surgical or traumatic wing amputations. Survival times of the 23 birds with an amputated wing (median: 1070 days, range: 68 days to 13 years and 1 month) were significantly (P = .02) longer than the survival times of the 404 non-amputated birds (median: 696 days, range 37 days to 27 years and 3 months). Complications occurred in 13 of 30 birds (43%) during the recovery period, with 9 of 30 (30%) birds developing life-threatening complications. Maladaptation to captivity was the leading cause of euthanasia during this period. After placement in captivity, 3/23 (13%) birds developed complications related to the amputation site. Based on this study, we conclude that some birds can tolerate partial or complete wing amputation, but the decision to place a bird in a captive setting should encompass the bird's ability to cope with human interaction and the availability of an adapted and safe enclosure for the animal.

Evaluation of prolonged immersion in tricaine methanesulfonate for juvenile goldfish (Carassius auratus) euthanasia.

OBJECTIVE: Doses of buffered tricaine methanesulfonate (MS-222) up to 1000 mg/L for 15 minutes are reported inefficient to produce euthanasia in goldfish. The goal of this study was to determine if goldfish can be euthanized by more prolonged immersion in MS-222. ANIMALS: 24 healthy goldfish (weight range: 1 to 10 g) were randomly assigned to 4 groups of 6 fish. PROCEDURES: The first group (G1) was exposed to 500 mg/L buffered MS-222 for 15 minutes then placed in freshwater for 3 hours. The second (G2) and third groups (G3) were exposed to 1000 mg/L of buffered MS-222 for 15 minutes then placed in freshwater for 3 hours and 18 hours respectively. The fourth group (G4) was exposed to 1000 mg/L of buffered MS-222 for 60 minutes then placed in freshwater for 3 hours. Time to cessation and return of operculation were recorded. If the goldfish did not resume operculation, heart rate was evaluated by Doppler ultrasonic flow detector. RESULTS: Median times to apnea were 35 seconds at 1000 mg/L and 65 seconds at 500 mg/L. Re-operculation occurred only in G1 in 5 out of 6 individuals. All fish from G1, 3 fish from G2, 0 fish from G3, 1 fish from G4 had remaining heartbeats at the end of the observation period. CLINICAL RELEVANCE: Overall, a dose of 1000 mg/L of buffered MS-222 for 15 minutes was efficient to euthanize juvenile goldfish at 20 °C. Different fish body mass and water quality parameters might explain different results compared to previous studies.

Occurrence of Ulcerative Lesions in Sea Stars (Asteroidea) of theNorthern Gulf of California, USA.

To assess the variation of sea star (Asteroidea) populations in the Northern Gulf of California and look for evidence of sea star ulcerative lesions, counts of sea star species were recorded in 2019 using a standard belt-transect technique of 30 m2. During surveys, scuba divers also measured sea stars' diameter and examined them for ulcerative lesions. Ulcerative lesions were noted on Phataria unifascialis only. To verify changes in abundance and size of the two most abundant species, P. unifascialis and Pharia pyramidata, historical data from 2009, 2010, and 2016 were used as comparison and using the same methodology. To evaluate differences in abundance or diameter in sea star species over time, analysis of variance tests were used. We found a significant reduction in diameter for the species P. unifascialis and P. pyramidata over time (<0.0001), but only P. unifascialis also showed a significant decrease in abundance (P=0.018). The decrease in diameter recorded for these two species, along with the signs of ulcerative lesions found on one of them in 2019, suggest that a potential mortality event occurred and, as a result, new younger (i.e., smaller) recruits could be recovering the population. These results highlight the importance of population monitoring to understand complex reef community dynamics.

Fish Sedation and Anesthesia.

Veterinarians often need to sedate or anesthetize fish to perform physical examinations or other diagnostic procedures. Sedation may also be required to transport fish. Painful procedures require complete anesthesia with appropriate antinociceptive agents. Regulations and withdrawal times apply to food animal species in many countries. Specific protocols are therefore warranted in commercial fish versus ornamentals. Tonic immobility of elasmobranchs and electric anesthesia should never be used to perform painful procedures. Anesthetic monitoring in fish remains challenging. This review summarizes ornamental fish anesthesia and discusses techniques used in the commercial fish industry and in field conditions.

USE OF SYMMETRIC DIMETHYLARGININE TO DETECT RENAL LESIONS IN FISH: A PRELIMINARY STUDY IN BROOK TROUT (SALVELINUS FONTINALIS).

Symmetric dimethylarginine (SDMA) is an early marker for renal lesions in mammals. The objectives of this study were 1) to establish a reference interval of SDMA in healthy brook trout, Salvelinus fontinalis (Mitchill, 1814), and 2) to assess its sensibility as a marker of renal pathology. Plasma SDMA was quantified by liquid chromatography-mass spectrometry in 25 adult brook trout, including 20 fish displaying no renal histologic lesions, and five fish displaying chronic nonactive microscopic granulomas. The fish size (P = 0.30) and weight (P = 0.12) were not statistically different among groups, nor were SDMA values (P = 0.22). However, brook trout without microscopic renal lesions tended to have lower SDMA values (no lesions: mean = 24.9 µg/dL; lesions: mean = 31.4 µg/dL). The reference interval (90% confidence interval [90% CI]) for SDMA concentration in brook trout ranged between 10.0 µg/dL (90% CI: 5.4-14.7) and 39.8 µg/dL (90% CI: 34.8-43.9). These values were higher than those previously reported in other vertebrate species. Further research is needed to evaluate the use of SDMA as a marker of renal function in fishes.

Development and Testing of a Sedation Scale for Use in Rabbits (Oryctolagus cuniculus).

In biomedical research, rabbits are commonly sedated to facilitate a variety of procedures. Developing a sedation assessment scale enables standardization of levels of sedation and comparisons of sedation protocols, and may help in predicting sedation level requirements for different procedures. The goal of this study was to develop a rabbit sedation assessment scale using a psychometric approach. We hypothesized that the sedation scale would have construct validity, good internal consistency, and reliability. In a prospective, randomized, blinded study design, 15 (8 females, 7 males) healthy 1-y-old New Zealand white rabbits received 3 intramuscular treatments: midazolam (0.5 mg/kg; n = 6); midazolam (1.5 mg/kg)-ketamine (5 mg/kg; n = 7); and alfaxalone (4 mg/kg)-dexmedetomidine (0.1 mg/kg)-midazolam (0.2 mg/kg; n = 3). One rabbit received 2 treatments. A sedation scale was developed by using psychometric methods, with assessment performed by 6 independent raters who were blind to treatment. Final sedation scale items included posture, palpebral reflex, orbital tightening, lateral recumbency, loss of righting reflex, supraglottic airway device placement, toe pinch, and general appearance. The scale showed construct validity, good to very good interrater reliability for individual items (6 raters; intraclass correlation coefficient, 0.671 to 0.940), very good intrarater reliability (5 raters; intraclass correlation coefficient, 0.951 to 0.987), and excellent internal consistency (Cronbach α, 0.947). The sedation scale performed well under the conditions tested, suggesting that it can be applied in a wider range of settings (different populations, raters, sedation protocols).

PHARMACOKINETIC, PHARMACODYNAMIC, AND TOXICOLOGY STUDY OF ROBENACOXIB IN RAINBOW TROUT (ONCORHYNCHUS MYKISS).

Postoperative antinociception control in fish is currently suboptimal, as commonly used antiinflammatory drugs last for only a few hours at tested temperatures. Therefore, long-acting anti-inflammatory drugs, such as robenacoxib, could improve the welfare of fish. The pharmacokinetics, duration of antinociceptive action, and potential adverse effects of robenacoxib were evaluated through two prospective randomized blinded trials in rainbow trout (Oncorhynchus mykiss). Six healthy rainbow trout received a single IM administration of robenacoxib (2 mg/kg), and two control fish received the same volume of saline IM. Blood samples were collected at predetermined time points for 5 d. Plasma robenacoxib concentrations were measured using high-performance liquid chromatography-high-resolution hybrid orbitrap mass spectrometry and noncompartmental pharmacokinetic analysis. Ten additional rainbow trout received an intralabial injection of 0.05 ml of 2% acetic acid following a previously validated nociceptive model. The treated group (n = 6) received 2 mg/kg of robenacoxib IM and the control group (n = 4) received an equivalent volume of saline IM. The behavior, appetite, and opercular rate of the fish were evaluated every hour for 5 h, then once daily for 3 d. All 12 treated trout and 6 controls underwent histopathologic evaluation. Average maximum plasma concentration (Cmax) was 329.9 ± 137.3 ng/ml observed at 2.1 ± 0.7 h (Tmax) and terminal half-life was 12.6 ± 2.27 h. Plasma concentrations described as antinociceptive in domestic carnivores were measured for 3-4 d. This dose was associated with a significant decrease in rocking behavior (P = 0.017). No adverse effects were detected clinically nor on histopathology. Robenacoxib administered IM at 2 mg/kg appears to be safe and may provide an antinociceptive effect in rainbow trout. This study presents a new therapeutic option to provide long-lasting antinociception in rainbow trout.

A PRELIMINARY STUDY OF INTRINSIC AND EXTRINSIC FACTORS INFLUENCING INTRAOCULAR PRESSURE IN BROOK TROUT (SALVELINUS FONTINALIS).

Reference intervals of intraocular pressure (IOP) are poorly described in piscine species as the factors that may influence it. Rebound tonometry was used to measure IOP in 28 adult brook trout (Salvelinus fontinalis) anesthetized in a buffered solution of 60 mg/L tricaine methanesulfonate (n = 16) or restrained with electronarcosis (n = 12) at 16 mA. There was no significant effect of the eye side, sex, fish origin, and body weight, but IOP values were significantly higher with electronarcosis (mean ± SD: 16.4 ± 5.0 mm Hg) than with immersion anesthesia (10.8 ± 3.3 mm Hg; P = 0.0017). The same restraint method should be used for comparison with previously published IOP values or when evaluating individual variations over time.

Clinical Reptile Behavior.

Reptile behavior varies widely among the approximately 11,000 species of this class. The authors' objective is to allow practitioners to discriminate between normal and abnormal behaviors in reptiles. Some of the most common reasons for presentation of behavioral issues are discussed, including hyperactivity, self-mutilation, biting, repetitive behaviors, and postural abnormalities. Medical problems and suboptimal husbandry causing abnormal behaviors should be ruled out by attending veterinarians. Addressing behavior issues involves determining a differential diagnosis through a systematic approach, which then allows implementation of necessary environmental changes including enrichment, developing plans for behavior modification and biomedical training, and medication when appropriate.

Abnormal Repetitive Behaviors and Self-Mutilations in Small Mammals.

Self-mutilation and abnormal repetitive behaviors in small mammals are challenging conditions for veterinary practitioners. The etiology may be difficult to identify, and the treatment is often unrewarding unless the specific underlying cause can be found. Reinforcement of the abnormal behavior may also complicate the treatment. However, medical causes, including painful conditions, should be investigated thoroughly. Owing to the small blood volume of many small exotic mammals and the associated risk of hypovolemia in case of hemorrhage, an hospitalization with potent multimodal analgesia and physical barriers to prevent self-mutilation is often warranted. Psychogenic drugs may be useful in some cases.

Altered prolactin and androgen receptors expression in companion rat benign mammary tumours.

Benign mammary tumours are among the most common tumours of companion rats (Rattus norvegicus domestica), as well as a major animal welfare concern and euthanasia. The first objective of this study was to evaluate the expression of oestrogen, progesterone, androgen, and prolactin receptors in neoplastic and normal mammary gland tissues and compare the expression of these receptors between groups. The second objective was to determine if the expression of these receptors in neoplastic mammary gland tissue correlates with overall survival and occurrence of an additional mass after initial mammary mass excision. The third objective was to determine if the expression of oestrogen, progesterone, androgen and prolactin receptors was associated with mammary tumor clinical parameters or with the age of the animals. Thirty-two benign mammary tumours were collected from companion rats and submitted for immunohistochemistry staining of prolactin receptor, oestrogen receptor alpha (ERa), progesterone and androgen receptors (AR). Allred score were obtained for mammary tumours (n = 32) and surrounding normal mammary tissue (n = 20) when present. Prolactin receptor expression increased significantly with mammary gland tumorigenesis (P < .0001), while AR expression decreased with tumorigenesis (P < .0001). Lower expression of ERa in tumor stroma was associated with shorter survival (P = .02). Hormonal receptor expression was not significantly associated with age, mass diameter, location nor likelihood of additional mass development. Further studies should investigate the effects of prolactin antagonists in a prospective study involving companion rats with benign mammary tumours.