Internal Parasites of Sympatric Bison, Bison bison, and Cattle, Bos taurus

Dirk Van Vureni1 and Cheryl A. Scott2

IDepartment of Wildlife, Fish, and Conservation Biology, University of California. Davis, California 95616

2School of Veterinary Medicine. University of California, Davis, California 95616

Van Vuren, Dirk and Cheryl A. Scott, 1995. Internal parasites of sympatric Bison, Bison bison, and Cattle, Bos taurus.

Reprinted from The Canadian Field-Naturalist, 1995;109(4):467-469.


Bison (Bison bison) and Cattle (Bos taurus), though closely related are ecologically different so we hypothesized that they would differ in prevalence of disease-causing organisms. We compared internal parasites of sympatric Bison and Cattle in the Henry Mountains, Utah by screening feces for parasites. We identified five taxa of parasites (Eimeria bovis, E.zuernii, Fasciola hepatica, order Strongylida. Trichuris; spp.). Prevalences differed between Bison and Cattle, especially those parasites associated with water. Likely causes are differences in host suitability and ecological differences between Bison and Cattle that affected the probability of transmission.

Key Words: Bison, Bison bison, Cattle, Bos taurus, parasites, disease, Utah.

Internal Parasites of Sympatric Bison, Bison bison, and Cattle, Bos Taurus

Bison (Bison bison) once numbered in the tens of millions and roamed throughout much of North America (Roe 1970). Indiscriminate slaughter during the 1800's resulted in near-extinction: by 1900 only a few hundred Bison remained. Intensive efforts narrowly averted extinction and numbers recovered to about 100 000 (Dary 1989). Most Bison today, however, are confined by fences on wildlife refuges or are intensively managed on private lands for commercial purposes: only a handful of herds are free-ranging.

Bison carry diseases that also may occur in domestic Cattle (Tessaro 1989), and controversies have arisen about the possibility of disease transmission between free-ranging Bison and neighboring cattle in several localities, including Utah (Popov and Low 1950; Nelson 1965). Yellowstone and Grand Teton National Parks (Thorne et al. 1991 ), and Wood Buffalo National Park (McCormack 1992). Although Bison and Cattle are similar in many respects, information on diseases of Cattle cannot necessarily be extrapolated to Bison (Tessaro 1989: indeed, the host-disease relationship in Bison differs markedly from that of Cattle (Meagher and Meyer 1994: Meyer and Meagher 1995). Further, ecological and behavioral differences between Bison and Cattle may affect disease transmission (Meagher and Meyer 1994). For example, when Bison and Cattle occur in the same area they may forage in different localities because of differing responses to forage availability, slope, and distance to water (Van Vuren 1982).

Bison harbor a variety of disease-causing parasites that also occur in Cattle (Tessaro 1989). Our objective was to compare prevalences of internal parasites in sympatric free-ranging Bison and Cattle in the Henry Mountains, Utah. Bison and Cattle differed in local distribution: in particular, Cattle were more closely associated with water (Van Vuren 1982). We hypothesized that prevalence of internal parasites would differ between Bison and Cattle, especially parasites associated with water.


The Henry Mountains (38°5'N. I 10°50'W), Garfield County, rise above the deserts of the surrounding Colorado Plateau to a maximum elevation If 3540 m. The lower slopes are about 1800-2400 m elevation and support extensive Pinyon Pine (Pinus dulis) and juniper (Juniperus spp.) woodlands. Large areas of these woodlands have been mechanically cleared and seeded to exotic forage species, chiefly Crested Wheatgrass (Agropyron desertorum) and Alfalfa (Medicago sativa). The climate is arid; annual precipitation in pinyon-juniper woodlands averages only about 25-40 cm. Surface water is scarce and is available only at a few widely scattered springs and small streams (Nelson 1965). Our study was conducted in the upper drainages of Sweetwater and Bullfrog creeks, on the western slope of the Henry Mountains.

The Henry Mountains have been used as summer rage by Cattle since the late 1800s. In recent years most Cattle grazing has occurred in and near areas that have been cleared and seeded. Bison were introduced in the 1940s, and the herd currently numbers several hundred. Although the Bison range widely, they frequently graze in areas that are also grazed by Cattle, especially cleared and seeded areas on the western slopes of the mountains (Van Vuren and Bray 1986); the two species sometimes feed within 2O m (Van Vuren 1982). Bison are migratory and spend winters primarily in the deserts to the west and southwest (Van Vuren and Bray 1986). Our study area was located at intermediate elevations that are used by Bison year-round. Cattle graze from June to October, then are moved to lower elevations where Bison usually do not occur. The Cattle from which fecal samples were obtained that had not been treated for parasites for two years prior to this study. The Bison had never been treated for parasites, and a screening of feces from eight Bison in 1962 revealed no parasites (Nelson 1965).

During 8-12 September 1993 we collected one fresh fecal sample from each of 51 Bison and 44 Cattle, We usually did not have sufficient time to determine age class or sex because most Cattle and all Bison were wary and stampeded when approached. About 20 g of fecal material were collected from the center of each fecal deposit and preserved by mixing with 60 ml of 10% formalin (Foreyt 1986). Samples were stored 150-200 days before analysis.

Fecal samples were screened for the presence of parasites using floatation. Sedimentation, and trichrome stain procedures (Brown and Neva 1983; Georgi and Georgi 1990). Parasites were floated using saturated zinc sulfate, then detected by light microscopy at 45x.. For sedimentation, 10% formalin was added to the fecal sample, then parasites were detected by light microscopy at 45x. Material from each of the sedimentation samples was smeared on two coverslips using polyvinyl alcohol, then stained using trichrome stain; each coverslip was scanned for 5 minutes under a light microscope at lOOx. Ova, oocysts, and trophozoites were identified with the aid of Georgi and Georgi (1990). A three-way contingency table (Sokal and Rohlf 1981) was used to determine if parasite prevalence differed between Bison and Cattle.


Five parasite taxa were identified. Eimeria bovis. E.zuernii, Fasciola hepatica. order Strongylida. and Trichuris spp. (Table I ); all five can cause diseases in Cattle (Georgi and Georgi 1990). Two of the parasites identified (E. bovis and E.zuermii) were found only in Cattle feces, one (Trichuris spp.) was found only in Bison feces, and two (Strongylida and Fasciola hepatica) were found in feces of both Bison and Cattle (Table I). Prevalences were low except for Strongylida, which occurred in 5I % of Bison feces (Table I ).

Parasite prevalence differed between Bison and Cattle; we rejected the null hypothesis that for a given parasite taxa, host species and prevalence were independent (G=26.8.df = 5. P<0.001 ). Twenty-three percent of Cattle feces contained Eimeria bovis. E. zuernii, or F. hepatica, compared with only 4% of Bison feces (G-test of independence,G=8.I,dj= 1, P<0.005).

TABLE I. Prevalence (0/c) of parasites in fecal samples from free-ranging Bison (n = 51) and Cattle (n = 44) in the Henry Mountains, Utah.

Bison Cattle Protozoa
Eimeria bovis O 5 E. :uernii 0 7 Trematoda
Fasciola hepulica 4 14 Nematoda
Strongylida 51 16 Trichuri.\. spp. 4 0


The high prevalence in Bison feces of Strongylida is consistent with results from Yellowstone National Park, where 80% of Bison examined carried Strongylus spp. (Zaugg et al. 1993). The low prevalence of Fasciola hepatica and Trichuris spp. in Bison also is consistent with other studies (Locker 1953; Zaugg et al. 1993). No protozoans were found in Bison feces, an unexpected result because both Eimeria bovis and E. zuernii were common among Bison in Montana (Penzhom et al. 1994).

As predicted, parasite prevalence differed between Bison and Cattle. One cause may be differing host-parasite relationships. Bison and Cattle, although closely related (Wall et al. 1992), differ substantially in genetics (Cronin and Crockett 1993), metabolism (Christopherson et al. 1978), digestive physiology (Schaefer et al. 1978), and rumen microbial populations (Towne et al. 1988); perhaps they also differ in suitability as hosts for parasites.

We suggest that ecological and behavioral differences also are important. Bison and Cattle mostly use different winter ranges, and they may have acquired different parasites accordingly. Morever, although they occur in the same general area during summer. Bison and Cattle in the Henry Mountains exhibit pronounced differences in local distribution (Van Vuren 1982). Cattle are relatively sedentary and graze primarily on gentle slopes near water. Bison, in contrast, roam widely and often graze localities that are on steep slopes, far from water or both (Van Vuren 1982). Because internal parasites often are transmitted on ingested food differences in foraging ecology between Bison and Cattle may affect transmission. Further. Cattle are more closely associated with water than are Bison (Van Vuren 1982). Life cycles of three of the parasite taxa identified require relatively mesic or even aquatic environments; transmission of Eimeria bovis and E. zuernii is promoted by high levels of moisture in the environment (Kheysin 1972), and the intermediate host of F. hepatica is an aquatic snail (Georgi and Georgi 1990). Prevalence of these parasites was significantly higher in Cattle than in Bison.

Disease transmission between Bison and Cattle has been demonstrated in closely-confined situations (Davis et al. 1990). But, because some ecological differences cannot be expressed in confinement, such evidence has uncertain relevance to free-ranging animals. Bison and Cattle are different species and their internal parasites differ accordingly. Perhaps ecological differences can be exploited to reduce disease transmission between Bison and Cattle.

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