Comparative Blood Characteristics of Ranched and Free-Ranging American Bison (Bison bison)

James G. Sikarskie, DVM, MB,. Tjaart W. Schillhorn van Veen, DVM, PhD,. Gijsbertus van Selm, MB,. Michael D. Koch, B Vet Med, MPVM


Blood samples were obtained from 20 bison (Bison bison) from a ranch in northern lower Michigan, as well as from 20 free-ranging bison of the same sex and similar age from the Badlands National Park in South Dakota. Hematologic and serum biochemical values were determined. The values were comparable in both groups, except for those for BUN, aspartate transaminase, and phosphorus, which were significantly (P < 0.001) higher in the ranched bison than in the free-ranging bison. These differences were attributed to nutritional effects. Impact of age on blood characteristics was assessed in the ranched bison only by comparing values from calves weighing less than 185 kg with those from bison weighing more than 185 kg. Calves had significantly (P < 0.001) higher values for phosphorus and RBC counts and lower total protein values than adults. Adult bison had higher eosinophil and neutrophil counts with lower numbers of lymphocytes, suggestive of a stress leukogram, whereas calves had the typical bovine neutrophil:lymphocyte ratio.

American bison (Bison bison) or buffalo are gaining popularity as a food animal, largely as a result of owners' claims that bison meat has less fat and cholesterol and is higher in protein and thiamine than beef. The increased demand by health-conscious Americans for this meat has resulted in rapidly increasing prices over the past 3 years at many of the buffalo sales in the United States and sparked a revival of interest in raising this once nearly extinct species.

The increased popularity of bison has challenged many veterinarians, not only with respect to handling and restraint of these animals, but also regarding clinical diagnosis and interpretation of clinicopathologic values. Bison can be handled like range cattle, but require stouter equipment and may be stressed more by restraint. Inadequate facilities make routine collection of blood difficult and potentially dangerous to the handler and to the animal. Bison are difficult to anesthetize, especially when they are excited and may require 5 to 10 times the dose of xylazine used on domestic cattle of similar weight.

In addition to the risks to the animal, it is well known that handling and use of anesthetic agents can effect the hematologic and biochemical values of blood obtained from the animals. Quality and quantity of forage also can effect these values, which have been used by wildlife managers to assess the quality of the habitat in which animals live.

Normal hematologic and serum biochemical values for wild bison on the range under experimental conditions and in zoos have been reported. The purpose of the study reported here was to determine blood values of apparently healthy ranched bison from samples collected while the bison were physically restrained and compare these values with those samples collected from similarly handled wild bison on the range in the western United States. Impact of age on blood values was evaluated for the ranched bison by comparing samples taken from bison weighing less than 185 kg with those from animals weighing more than 185 kg.

Materials and Methods

Ranched bison - Blood samples were obtained from the jugular vein of each of 20 (10 calves and 10 adults) bison selected from a herd of 150 bison on a ranch in northern lower Michigan. All bison were born and raised on the ranch. The bison were rounded up the evening prior to sample collection using grain as bait. Facilities for handling were a corral and a restraint chute, similar to those used for beef cattle. Blood was collected in sterile tubes with and without EDTA. The EDTA tubes were cooled to approximately 4 C, using icepacks. Thin blood smears were made, using standard technique. The tubes without anticoagulant were left at 20-23 C for 4 to 6 hours, at which time serum was removed and refrigerated. Serum was analyzed within 24 hours and unused portions were stored at -20 C for later use.

Free-ranging bison - Blood smears and serum were obtained from 20 bison that were rounded up from the Badlands National Park in South Dakota. These bison had not been nutritionally supplemented and foraged on historic bison habitat. Those chosen for study were paired by gender and, as closely as possible, by age with the ranched bison. They were handled in a similar fashion and at the same time of year (late summer) as the ranched bison. After blood was obtained, prepared blood smears were fixed in alcohol and serum was frozen.

Because serum from the free-ranging bison had been frozen prior to analysis, a subgroup of serum samples from the ranched bison was thawed and reanalyzed after the same duration of time in the freezer as the samples from the free-ranging bison to account for any changes related to handling or age of the samples.

Laboratory analysis - Analyses were performed by the same laboratory to help minimize errors relating to handling and technique. Hematologic values for RBC, WBC, and hemoglobin (Hb), were determined by use of an automatic cell counter; however, PCV values were determined via centrifugation. These values were not obtained for the free-ranging bison because only slides and serum were available. Fixed blood smears were stained with Wright-Giemsa stain on an automatic slide stainer; WBC differential counts were determined from these slides and used to determine absolute values for cell types. Serum was analyzed to determine concentrations of calcium, phosphorus, magnesium, aspartate transaminase (AST), sorbitol dehydrogenase (SDH), BUN, glucose, albumen, and total protein (TP) with a serum chemistry analyzer, using reagents and techniques described by the manufacturer. An electrolyte analyzer with ion-specific electrodes was used to determine values for sodium, potassium, and chloride. The impact of age was assessed by allotting the ranched bison to 2 groups; values from calves weighing less than 185 kg were compared with values from bison weighing more than 185 kg. Data were analyzed using a data management program and a statistical program.

Significance was determined, using the Student t test with P < 0.001 for all analyses.


Values obtained from frozen serum from the ranched bison were within the confidence limits for quality control standards for laboratory equipment and technician's error when compared with values obtained from the same samples prior to freezing. The activity for SDH was not obtained for the frozen samples, because assays for SDH, are meaningless unless fresh samples are used.

Values obtained from serum analysis of ranched and free-ranging bison are listed in Table 1 and hematologic values are listed in Table 2. Serum biochemical data (Table 3) and hematologic data (Table 4) are compared for calves and adults, but only for ranched bison where accurate weights and ages were available.


Analysis of blood characteristics of ranched bison, kept under conditions comparable with those used for beef cattle, revealed most serum biochemical and hematologic values to be similar to values from bison on the western range. Values for BUN, phosphorus, and AST were higher in the ranched bison. Phosphorus and BUN values in cattle and bison are related to the amount of crude protein in the diet. Ranched bison in this study were grazing on a higher protein-mixed grass/legume pasture, whereas free-ranging bison were on late summer prairie grasses. The AST activities are a measure of cell damage and necrosis in liver and muscle and usually are higher in wild animals than in similarly restrained domestic animals. As the handling of all animals in this study was comparable, differences in AST activity were attributed to nutrition of the animals. Myopathies associated with selenium deficiency have been determined to increase AST values. Mean serum selenium values were 0.026 ug/ml in the ranched animals, compared with 0.099 ug/ml in the free-ranging bison and findings of selenium deficiency observed in the ranched herd are published elsewhere. One animal in this study had clinical signs of capture myopathy after handling. The tissue damage attributable to these, myopathies could explain the higher AST values in ranched bison than in the free-ranging bison.

Table 1 – Serum biochemical data for ranched bison in Michigan and free-ranging bison in South Dakota


Ranched bison 

Free-ranging bison 

Total protein (g/dl)

7.14 ± 0.90

7.46 ± 0.81

Albumin (g/dl)

4.10 ± 0.33

4.20 ± 0.30

Globulin (g/dl)

2.95 ± 0.80

3.25 ± 0.83

BUN (mg/dl)

21.60 ± 3.64

17.15 ± 3.37*

Sorbital dehydrogenase (IU/L)

28.71 ± 8.10


Aspartate transaminase (IU/L)

109.95 ± 35.75

80.40 ± 16.12*

Glucose (mg/dl)

153.80 ± 49.12

134.50 ± 48.50

Calcium (mg/dl)

9.68 ± 0.76

9.69 ± 0.47

Magnesium (mg/dl)

2.67 ± 0.34

2.79 ± 0.45

Phosphorus (mg/dl)

6.50 ± 1.62

4.37 ± 1.54*

Potassium (mEq/L)

4.95 ± 0.80

5.57 ± 0.71

Sodium (mEq/L)

145.00 ± 2.14

146.30 ± 4.45

Chloride (mEq/L)

105.90 ± 1.97

107.10 ± 3.43

*Significantly (P < 0.001) different from ranched bison.
ND = not determined. Data are expressed as mean = SEN.


Table 2 Hematologic data for ranched bison in Michigan and free-ranging bison in South Dakota

Value Ranched bison (n=20) Free-ranging bison
PCV (%)

44.65 ± 3.93


Hemoglobin (g/dl)

17.04 ± 1.62


RBC (x 106/ μl)

10.19 ± 1.87


WBC (x 103/ μl)

10.56 ± 3.62


Lymphocytes (x 103/ μl)



Neutrophils (x 103/ μl)



Eosinophils (x 103/ μl)



Monocytes (x 103/ μl)



Lymphocytes (%)

44.00 ± 16.38

50.80 ± 11.66

Neutrophils (%)

43.80 ± 15.46

41.75 ± 11.47


6.60 ± 5.31

4.10 ± 2.67

Monocytes (%)

0.65 ± 0.75

3.25 ± 3.91

Date are expressed as mean ± SEM
ND = not determined


Table 3 – Serum biochemical data for young and adult ranched bison

Value Calves < 185 kg 
(n = 10)
Adults > 185 kg
(n = 10)
Total protein (g/dl) 6.54 ± 0.72 7.72 ± 0.76*
Albumin (g/dl) 4.01 ± 0.37 4.20 ± 0.24
BUN (mg/dl) 20.40 ± 2.57 22.80 ± 4.12
Sorbital dehydrogenase (IU/L) 29.40 ± 8.06 27.90 ± 8.14
Aspartate transaminase (mg/dl) 102.90 ± 37.20 117.00 ± 36.70
Glucose (mg/dl) 158.90 ± 59.80 147.40 ± 37.00
Calcium (mg/dl) 10.09 ± 0.94 9.36 ± 0.45
Magnesium (mg/dl) 2.72 ± 0.33 2.60 ± 0.42
Phosphorus (mg/dl) 7.83 ± 1.01 5.54 ± 1.24*
Potassium (mEq/L) 5.19 ± 0.84 4.72 ± 0.67
Sodium (mEq/L) 145.20 ± 2.56 144.80 ± 1.60
Chloride (mEq/L) 104.80 ± 1.40 107.00 ±1.84

Significantly (P < 0.001) different from calves. Data are expressed as mean ± SEM.


Table 4 – Hematologic data for young and adult ranched bison

Value Calves < 185 kg 
(n = 10)
Adults > 185 kg 
(n = 10)
PCV (%)

46.30 ± 3.69

43.00 ± 3.20

Hemoglobin (g/dl)

17.59 ± 1.58

16.49 ± 1.36

RBC (x 106/ μl)

11.67 ± 1.24

8.72 ± 0.84*

WBC (x 103/ μl)

9.64 ± 2.99

11.48 ± 8.78

Lymphocytes (x 103/ μl)



Neutrophils (x 103/ μl)



Eosinophils (x 103/ μl)



Monocytes (x 103/ μl)



Lymphocytes (%)



Neutrophils (%)






Monocytes (%)



*Significantly (P < 0.001) different from calves.
Data are expressed as mean ± SEM.

The ranched bison weighing less than 185 kg had higher phosphorus and lower total protein values, compared with those of the heavier and presumed older bison. These findings were typical of differences for young, actively growing animals. Calves also had significantly (P < 0.001) higher RBC counts than adults, which is a common finding in cattle.13 Calves had the typical cattle leukogram with lymphocytes outnumbering neutrophils, whereas adults had higher numbers of neutrophils and eosinophils. These findings could be explained by the effects of stress, because there was no apparent disease in the adults, and calves had not been handled prior to blood collection, plus they were calmed by the presence of their mothers. The effects of stress appear to be similar when evaluating the differentials from wild bison, although WBC counts and absolute values are not available for a precise comparison. It is important to consider the effects of stress on values from samples collected from any excited, non-domestic species.


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