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Journal of Wildlife Diseases, 47(3), 2011, pp. 685–689# Wildlife Disease Association 2011

Hematologic and Blood Chemistry Reference Values for Free-ranging

Muskrats (Ondatra zibethicus)

Adam A. Ahlers,1,2,4 Mark A. Mitchell,3 Robert L. Schooley,1 Edward J. Heske,2 and Jeffrey M.Levengood2,3 1Department of Natural Resources and Environmental Sciences, University of Illinois, 1102 S.Goodwin Avenue, Urbana, Illinois 61801, USA; 2Illinois Natural History Survey, University of Illinois, 1816 SouthOak Street, Champaign, Illinois 61820, USA; 3College of Veterinary Medicine, University of Illinois, 2001 SouthLincoln Avenue, Urbana, Illinois 61802, USA; 4Corresponding author (email: aahlers2@illinois.edu)

ABSTRACT: Baseline hematologic and serumchemistry values are used by veterinarians andwildlife biologists to identify abnormally high orlow levels of particular blood parameters in atarget species. This vital information can assistanimal care providers in making informeddecisions on the care of wildlife and help todetermine diagnoses for certain illnesses. Pub-lished blood parameter values are not availablefor wild-caught muskrats (Ondatra zibethicus).We measured 27 blood parameter values from29 free-ranging, riparian muskrats caught fromJune–November 2008 in east-central Illinois,USA, and compared mean values betweenadults and juveniles. Adult muskrats had higherlevels of globulins (F1,2756.394, P#0.018) andeosinophils (F1,2556.883, P#0.015) than didjuvenile muskrats, possibly because of in-creased exposure to parasites and allergensover time.

Key words: Blood chemistry, hematology,muskrat, Ondatra zibethicus, riparian.

Values for blood parameters in manyspecies of wildlife have been documentedto provide baseline measurements forveterinarians and biologists (e.g., Weberet al., 2002). However, data providingessential baseline hematologic and serumchemistry values for wild-caught muskrats(Ondatra zibethicus) are not available.Borucinska et al. (1997) reported changesin key blood parameter values and clini-copathologic features for laboratory-accli-mated muskrats experimentally infectedwith Capillaria hepatica eggs but did notprovide baseline values for either the testor control group. MacArthur (1983) andMacArthur et al. (2003) documenteddifferences in six baseline blood parame-ters (hematocrit, hemoglobin, mean cellvolume, mean cell hemoglobin, red blood

cell count, and mean cell hemoglobinconcentration) while comparing body ox-ygen stores between treatment groups oflaboratory-acclimated muskrats. Althoughbaseline measurements were reported forthese six blood parameters, other param-eters exist that can provide veterinariansand biologists with vital information re-quired to make informed decisions onhandling and care of this species. Weprovide reference values for 27 bloodparameters in 29 wild-caught riparianmuskrats in east-central Illinois, USA,and compare adult and juvenile muskratvalues in those key blood parameters.

This study was conducted in accordancewith the regulations specified by theUniversity of Illinois Animal Care andUse Committee (Protocol 07105). We live-trapped muskrats from June to November2008 in agricultural ditches and smallstreams in Champaign County, Illinois,USA (40u129N, 88u269W), as part of aconcurrent study of survival and move-ments. Immediately after capture, musk-rats were taken to a sterile surgicallaboratory at the Veterinary TeachingHospital at the University of IllinoisCollege of Veterinary Medicine (Urbana,Illinois, USA). Muskrats were examined inthe trap for changes in mentation, breath-ing pattern, and locomotion and trans-ferred to a handling bag to determineweight. Muskrat age was estimated byweight at capture, which is an effectivetechnique to determine muskrat ageduring the summer and fall trappingseason (Errington, 1939). Determining

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the sex of live juvenile muskrats is difficultand cannot be done with certainty for allindividuals (Dozier, 1942). Because of therisk of determining sex incorrectly, we didnot examine differences between thesexes. Muskrats were premedicated with0.2 mg/kg atropine sulfate (Vedco Inc., St.Joseph, Missouri, USA) and 0.05 mg/kgmedetomidine (DormitorH, Pfizer AnimalHealth, New York, New York, USA) byintramuscular injection. General anesthe-sia was induced once the animal’s rightingreflex had diminished using 5% isoflurane(Hospira Inc., Lake Forest, Illinois, USA)and oxygen (0.6 l/min) via facemask.Muskrats were maintained during thesurgical procedure with 1–2% isofluraneand oxygen (0.6 l/min). Once the animalswere anesthetized, they were given athorough physical examination, and theirbody condition assessed. Before surgery,we administered 1.0 mg/kg of meloxicam(Boehringer Ingelheim Vetmedia Inc., St.Joseph, Missouri, USA) subcutaneouslyand 0.1 ml of penicillin G benzathineand penicillin G procaine (Bimeda Inc.,Irwindale, California, USA) via intramus-cular injection for postoperative analgesiaand perioperative antibiotic prophylaxis,respectively. Each animal was asepticallyprepared for surgery and marked with a14-g radiotransmitter (Model M1215; Ad-vanced Telemetry Systems, Isanti, Minne-sota, USA) by surgical implantation intothe peritoneal cavity (MacArthur, 1980;Lacki et al., 1989).

Before recovery, blood samples (1.5 ml)were collected from the cranial vena cavaeusing a 25-gauge needle fastened to a 3-mlsyringe. Samples were separated andstored in ethylenediaminetetraacetic acid(EDTA) and lithium heparin microtainertubes (Becton Dickinson, Franklin Lakes,New Jersey, USA). Samples were pro-cessed immediately after collection. Sam-ples stored in lithium heparin werecentrifuged to separate plasma from thecells and processed for plasma chemistryanalysis (VetScan, Abaxis, Inc., UnionCity, California, USA). Samples stored in

EDTA tubes were processed for a com-plete blood count (Cell Dyn 3700, AbbottDiagnostics, Santa Clara, California, USA)and differential. Measured hematologicparameters included the following values:white blood cell (WBC) count, neutrophils(NEU), lymphocytes (LYM), monocytes(MONO), eosinophils (EOS), basophils(BASO), red blood cell (RBC) count,hemoglobin (HGB), hematocrit (HCT),mean corpuscular volume (MCV), meancorpuscular hemoglobin (MCH), meancorpuscular hemoglobin concentration(MCHC), and red cell distribution width(RDW). Measured blood plasma chemis-try parameters included albumin (ALB),alkaline phosphatase (ALP), alanine trans-aminase (ALT), amylase (AMY), totalbilirubin (TBIL), blood urea nitrogen(BUN), calcium (CA), phosphorus(PHOS), creatinine (CRE), glucose(GLU), sodium (NA), potassium (K), totalprotein (TP), and globulin (GLOB). Ati-pamezole (2.5 mg/kg; Antisedan, PfizerAnimal Health) was administered follow-ing blood collection to reverse the effectsof medetomidine, and isoflurane wasdiscontinued. Individuals were continuedon oxygen until they had a chewing reflexand were then returned to their traps andheld for $2 hr before being released attheir site of capture.

Kolmogorov-Smirnov tests were per-formed to determine whether data werenormally distributed. Nonnormal datawere log-transformed before analysis.For normally distributed data, we reportthe mean, SD, minimum, and maximum.For nonnormal data, we report themedian, minimum, and maximum. One-way analysis of variance was used to testthe null hypothesis of no significantdifferences between blood parametersbetween adult and juvenile muskrats. Dataanalysis was performed using the statisticalsoftware SPSS 16.0 (SPSS Inc., Chicago,Illinois, USA), and differences in blood-parameter values were considered signif-icant at P,0.05.

We collected sufficient blood to evalu-

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ate plasma chemistries for 29 muskrats (24juveniles [83%] and 5 adults [17%]) andhematologic parameters for 28 muskrats(22 juveniles [79%] and 6 adults [21%]).Although our sample sizes are small, theyshould be adequate for detecting moder-ate to large differences in blood-parame-ter values between age classes, and thatinformation may be important for gener-ating hypotheses for future studies (Bis-sonette, 1999). We omitted the AMY valuefor one juvenile muskrat (1,756.00 IU/l),which was .8 SD away from the mean(280.74, SD5171.84). The EOS and AMYvalues were log-transformed before anal-ysis. Adult muskrats had higher meanGLOB values (2.48 g/dl) than did juvenilemuskrats (1.89 g/dl; F1,2756.394, P#

0.018). Adults also had higher EOS values(median50.13%) than did juveniles (me-dian50.03%; F1,2556.883, P#0.015).There were no differences between adultand juvenile muskrats for the remainder ofthe examined parameters, so data werecombined (Tables 1 and 2).

Our results for HGB, HCT, RBC,MCV, and MCH values (Table 2) wereconsistent with those reported by Mac-

Arthur (1984) in laboratory-acclimatedmuskrats. However, the MCHC findingfor muskrats in our study (Table 2) wasmuch lower than those reported byMacArthur et al. (2003) for both surface-swimming and diving muskrats. As ameasure of the concentration of hemoglo-bin in a given volume of packed red bloodcells, MCHC increases with exercise insome species (Munoz et al., 2008). Ani-mals were tested by MacArthur et al.(2003) during diving and swimming exer-cises, which may have elevated theirMCHC. MacArthur (1984) also reportedseasonal differences in HCT, RBC, andMCHC values (significantly higher in thewinter). However, because of our smallsample size, we were unable to compareseasonal differences in blood parameters.

Although we did not measure parasiteburdens, differences between adult andjuvenile GLOB and EOS levels were likelyattributable to longer exposures to patho-gens by adults. Elevated levels of GLOBare expected in older animals becausetheir immune systems have been respond-ing to antigenic stimulation longer (Mitch-ell et al., 1999). Eosinophils are granulo-

TABLE 1. Plasma chemistry values obtained from 29 free-ranging muskrats (Ondatra zibethicus) in east-central Illinois, USA. Parameters did not differ between age classes except for globulin (GLOB).

Parametera Minimum Mean6SD Maximum

ALB (g/dl) 2.20 4.1360.56 5.00ALP (IU/l) 217.00 689.836315.58 1,389.00ALT (IU/l) 47.00 109.24657.47 345.00AMY (IU/l) 103.00 184.50b 799.00TBIL (mg/dl) 0.20 0.4860.14 0.70BUN (mg/dl) 3.00 16.9766.40 33.00CA (mg/dl) 8.30 9.2860.65 10.90PHOS (mg/dl) 7.10 10.6162.45 17.70CRE (mg/dl) 0.20 0.6260.19 1.20GLU (mg/dl) 29.00 240.79683.46 386.00NA (mEq/l) 136.00 149.7264.32 156.00K (mEq/l) 3.90 5.3060.97 8.00TP (g/dl) 4.80 6.1360.45 6.90GLOB (g/dl), adults 1.60 2.4860.63 3.20GLOB (g/dl), juveniles 1.10 1.8960.44 2.80

a ALB 5 albumin; ALP 5 alkaline phosphatase; ALT 5 alanine transaminase; AMY 5 amylase; TBIL 5 total bilirubin;BUN 5 blood urea nitrogen; CA 5 calcium; PHOS 5 phosphorus; CRE 5 creatinine; GLU 5 glucose; NA 5 sodium;K 5 potassium; TP 5 total protein; GLOB 5 globulin.

b For analysis of AMY values, n528; median value reported.

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cytes that are typically associated with thepresence of parasites (especially larvalmigrans), hypersensitivity, or allergenstimulation. Again, it is expected thatolder individuals would have an increasedlikelihood for exposure to parasites (e.g.,Toxoplasma gondii) or allergens (Little etal., 1998; Mitchell et al., 1999) and thusincreased EOS levels.

The mean WBC count in this muskratpopulation is similar to that reported forother rodents (Quesenberry et al., 2000).These muskrats were primarily neutro-philic, whereas other rodents are primarilylymphocytic (Quesenberry et al., 2000).This skewed NEU-LYM relationshipcould be associated with capture andhandling stress (Weber et al., 2002). Also,we observed an inverse mean CA (9.28 mg/dl) and PHOS (10.61 mg/dl) ratio (Ta-ble 1). Inverse CA:PHOS ratios can besuggestive of renal issues (e.g., Jara et al.,2002); however, we did not specificallyassess renal health in our muskrats.Inverse CA:PHOS ratios could be theresult of rhabdomyolysis associated withcapture and handling (Bartsch et al.,1977). However, further investigation is

necessary to determine whether such arelationship exists.

This research was funded by the USFish and Wildlife Service Federal Aid inWildlife Restoration Fund, Illinois De-partment of Transportation, and the Illi-nois Natural History Survey. The authorsthank M. Ulrich and J. Whittington fortheir technical assistance and Abaxis, Inc.,for supplying the rotors for analyzing thechemistries.

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TABLE 2. Hematologic values obtained from 28 free-ranging muskrats (Ondatra zibethicus) in east-centralIllinois, USA. Parameters did not differ between age classes, except for eosinophils (EOS).

Parametera Minimum Mean6SD Maximum

WBC (K/ml) 3.85 10.7865.02 25.20NEU (%) 2.64 8.8664.76 23.20LYM (%) 0.39 1.4960.79 3.78MONO (%) 0.10 0.3560.19 0.69BASO (%) 0.00 0.0260.02 0.05RBC (M/ml) 5.06 5.9560.54 6.98HGB (g/dl) 12.30 16.0661.47 19.50HCT (%) 36.60 46.6064.26 54.30MCV (fL) 72.30 78.3463.12 85.70MCH (pg) 24.30 26.9961.09 28.80MCHC (g/dl) 32.80 34.4760.75 35.90RDW (%) 12.30 14.0961.02 16.00EOS (%), adults 0.03 0.13b 0.24EOS (%), juveniles 0.00 0.03b 0.25

a WBC 5 white blood cell count; NEU 5 neutrophils; LYM 5 lymphocytes; MONO 5 monocytes; BASO 5 basophils;RBC 5 red blood cell count; HGB 5 hemoglobin; HCT 5 hematocrit; MCV 5 mean corpuscular volume; MCH 5

mean corpuscular hemoglobin; MCHC 5 mean corpuscular hemoglobin; RDW 5 red cell distribution width; EOS 5

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Submitted for publication 10 May 2010.Accepted 11 January 2011.

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