Congestive cardiomyopathy in the woodchuck, Marmota monax

Congestive cardiomyopathy was diagnosed during post mortem examination in eight of 149 adult woodchucks from New York. The eight woodchucks, four males and four females, died spontaneously without clinical signs of heart failure having been detected. The primary lesion was a grossly enlarged and dilated heart. Histologic lesions consisted of multifocal myocardial degeneration and necrosis. Secondary lesions of congestive heart failure were observed.     

Lymphosarcoma in the laboratory woodchuck (Marmota monax)

From 1979 to 1999,28 cases of lymphosarcoma were identified in the Cornell University woodchuck colony (prevalence rate: 152/100,000/yr). The prevalence of lymphosarcoma was similar in woodchucks not infected with the woodchuck hepatitis virus (WHV) and in chronic carriers of WHV. Males (13) and females (15) alike were affected (mean +/- SD age 4.7 +/- 2.92 years; range, 0.5 to 9 years). On the basis of the major organ system involved, woodchuck lymphosarcoma was classified as multicentric (12 cases, 43%), alimentary (5 cases, 18%), cranial mediastinal (5 cases, 18%), and miscellaneous (6 cases, 21%). A cutaneous form was not observed. Morphologic criteria similar to those of the Kiel classification were used for light microscopic classification. All Kiel categories-except the immunoblastic form-were found: 17 cases (61%) were centroblastic, and 6 were lymphocytic (21%). Other categories (centrocytic and plasmacytoid) were recognized less frequently. Immunophenotyping of 27 cases revealed 15 (56%) B cell (CD3-/CD79a+ or CD3-/BLA.36+), 7 (26%) T cell (CD3+/CD79a-/BLA.36-), and 5 (18%) non-T non-B cell (CD3-CD79a-/BLA.36-) lymphosarcomas. Lymphosarcoma in woodchucks develops at a higher rate than that observed in humans or companion animals, and WHV infection has no effect on prevalence. The anatomic and Kiel classification used in domestic species also can be used in woodchucks. Commercially available alpha-CD3, alpha-CD79a, and alpha-BLA.36 antibodies were useful for immunophenotyping woodchuck lymphosarcomas.     

Parasites of the laboratory woodchuck (Marmota monax)

The parasite burden of captive and colony-born woodchucks maintained in laboratory animal facilities was determined and compared to woodchucks recently trapped. Microfilariae of Ackertia marmotae in blood or dermis were most commonly observed in trapped woodchucks. There was a linear decrease in woodchucks positive for microfilariae after introduction in the laboratory colony, but even after 39 months, 53% were positive. Microfilaremia or microfilariderma were never observed in colony born woodchucks. Eggs or oocysts of Obeliscoides cuniculi, Citellina triradiata and Eimeria sp. were found by fecal flotation. The O. cuniculi population declined exponentially in captive woodchucks following colony entry, and this nematode was never found in colony-born woodchucks. However, low rates of infection with Citellina and Eimeria sp. were found in the colony-born group. Ixodes cookei, Oropsylla sp., and Androlaelaps sp. ectoparasites were observed commonly in recently trapped woodchucks, but were not present in any woodchucks maintained in the colony. Clinical disease associated with parasitic infection was not observed.     

The woodchuck, Marmota monax, as a laboratory animal

The woodchuck or groundhog (Marmota monax) has been used as a biomedical model for studies of obesity and energy balance, endocrine and metabolic function, central nervous system control mechanisms and cardiovascular, cerebrovascular and neoplastic disease. Methods of care of a woodchuck colony, techniques for handling, restraint, anesthesia, blood sampling and breeding were developed.     

Cerebral cysticercosis in a woodchuck (Marmota monax)

A juvenile woodchuck (Marmota monax) with vestibular signs was found in Woodbridge, Ontario (Canada) and later euthanized. At necropsy there was marked distortion of the right side of the skull, where a large, fluctuant, subcutaneous mass extended under the zygomatic arch and caudally from the right eye towards the right ear. The mass was multiloculated and contained a large number of tapeworm cysticerci, each about 1 to 2 mm in diameter. The third and lateral ventricles of the brain were dilated and contained large numbers of similar cysticerci. Based on the exogenous budding of cysts and the morphology of the scolex in each cyst, they were identified as cysticerci of Taenia crassiceps. This is the first report of cerebral cysticercosis in a woodchuck.     

Erthyrocyte changes in the hibernating woodchuck (Marmota monax)

Active woodchucks were maintained at 23 °C with a photoperiod of LD 12:12. Hibernating woodchucks were kept at 10 °C with a photoperiod of LD 8:16. Blood was collected and the erythrocytes were counted and measured.The data showed an increase in red blood cell count, a decrease in erythrocyte diameter and a decrease in mean corpuscular diameter during hibernation. The hematocrit was the same in both the hibernating and active woodchucks. It would appear that there are a greater number of smaller cells present in the circulation of the hibernating woodchuck as compared to that of the active woodchuck. This may result from the combined effects of increased life span, decreased destruction and continued, but slowed, production of red blood cells.     

Laboratory assessment of hepatic injury in the woodchuck (Marmota monax)

Normal reference values for total serum protein, albumin, cholesterol, alanine aminotransferase (ALT), aspartate aminotransferase (AST), sorbitol dehydrogenase (SDH), gamma glutamyl transferase (GGT), alkaline phosphatase (AP), and total bilirubin were established in 48 clinically healthy woodchucks. To validate the use of these biochemical tests in the woodchuck for assessment of liver injury, carbon tetrachloride was administered to produce hepatocellular necrosis and the common bile duct was surgically occluded to produce cholestasis. Biochemical tests were performed prior to experimental treatment and thereafter in surviving woodchucks for a period of 6 weeks. There were marked increases in the serum activities of AST, ALT, and SDH following carbon tetrachloride administration and all 3 enzymes appeared to be useful markers of acute hepatocellular injury. The predominate biochemical abnormalities in woodchucks with bile duct obstruction were hyperbilirubinemia, hypercholesterolemia and increased serum AP and GGT activities. The increase of GGT occurred earlier following bile duct obstruction and the magnitude of increase was greater than that of AP, suggesting that GGT would be the preferred serum enzyme test in the woodchuck for assessment of cholestatic liver injury.     

The influence of distance to burrow on flight initiation distance in the woodchuck, Marmota monax

We used woodchucks (Marmota monax) to test predictions of acost-benefit model of antipredator behavior that flight initiationdistance would increase with distance to refuge and with predatorapproach velocity. We also examined the effects of distanceto refuge and predator approach velocity on escape velocityand on both temporal and spatial margin of safety (expectedtime and distance between predator and burrow at the time ofthe woodchuck's arrival). The observer, assumed to be perceivedas a potential predator, approached juvenile woodchucks fromthe direction opposite to the burrow at a slow (1.24 m/s) orfast (1.79 m/s) walking pace. When the woodchuck started toflee, the observer recorded the woodchuck's distance from theobserver and from its burrow, the time spent running, and whetherthe woodchuck stopped before reaching its burrow. Flight initiationdistance increased consistendy with distance to the burrow overthe entire observed range (0–25 m) but was not significantlyaffected by observer approach velocity. Escape velocity wasnot significantly influenced by the observer approach velocityand was approximately constant over the range of 2–25m, but was slower for woodchucks less than 2 m from their burrows.Both temporal and spatial margins of safety increased with distancefrom the burrow. The temporal margin of safety increased withdistance from the burrow more rapidly for slow than for fastobserver approach velocity. Woodchucks fleeing from greaterthan 2 m usually stopped near the burrow before entering, butthose from closer distances usually entered directly. Theseresults support the assumption that antipredator behavior issensitive to the costs and benefits of alternative escape decisions.     

The parathyroid gland of the woodchuck (Marmota monax): a study of seasonal variations in the chief cells

The ultrastructure of the parathyroid chief cell in the woodchuck, Marmota monax, was studied during the four seasons of the year. Spring chief cells have stacks of granular endoplasmic reticulum, prominent multiple Golgi zones and many clumped mitochondria. Summer cells resemble those seen in the spring but the mitochondria are associated with stacks of granular endoplasmic reticulum. Multiple areas of stacked granular endoplasmic reticulum characterize the fall chief cells. Their Golgi zones are large and are associated with many dense core secretory granules. Lipoid vacuoles are frequently noted. Winter chief cells have secretory granules and phagolysosomes (dense bodies). Some of these cells contain stacked arrays of granular endoplasmic reticulum associated with mitochondria, others have only short segments. The above morphological findings are discussed in relation to those in other hibernators, the parafollicular (C) cell, and to the cyclic seasonal activities of the woodchuck.     

Stimulation of testicular function during the nonbreeding season in the woodchuck (Marmota monax)

Treatment of male woodchucks with a series of s.c. injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) induced testicular growth, sperm production and marked increase in serum testosterone levels in the fall, approximately 4 mo before the expected spontaneous onset of testicular activity. These results suggest that it may be possible to induce and/or maintain reproductive competence in this species outside of its normally brief breeding season.     

Hepatic lesions in woodchucks (Marmota monax) seronegative for woodchuck hepatitis virus

Livers from 128 captive woodchucks (Marmota monax) that were negative for serological markers of woodchuck hepatitis virus (WHV) were examined grossly and histologically. Livers from 19 additional seronegative woodchucks were examined only grossly. The most common finding (61% of histological specimens) was mononuclear cells in portal areas. Moderate to severe portal infiltrates in association with similar scattered mononuclear cell aggregates and extramedullary hematopoiesis, were present in woodchucks that had extrahepatic inflammatory lesions. We concluded that these changes represent a response to a variety of chronic infections and are not specific for WHV infection. Other findings included parasitic granulomas, focal and diffuse lipidosis, bile duct proliferation, lesions secondary to cardiovascular compromise, and vasculitis. Two woodchucks had neoplastic lesions.     

An infrared thermographic study of surface temperature in the euthermic woodchuck (Marmota monax).

Surface temperatures were measured in euthermic woodchucks (Marmota monax) using infrared thermography across a range of ambient temperatures from -10 degrees C to 32 degrees C. The woodchuck keeps surface temperature of the peripalpebral region uniformly high, while head and body surfaces change proportionally with ambient temperature. When ambient temperature was below 0 degrees C, all surface temperatures increased which prevents freezing. At no point did the animals appear to be unable to regulate heat exchange. This species appears to be especially well adapted to the higher temperatures it encounters in its range. Vasomotion in the feet and to a lesser extent in the pinnae was used to regulate heat loss. At ambient temperature of 32 degrees C, mean temperatures of nose surfaces were 0.2 degrees C and 0.3 degrees C less than ambient temperature suggesting a type of counter current cooling mechanism may be present.