Seroprevalence of OHV-2, BVDV, BHV-1, and BRSV in ranch-raised bison (Bison bison).

Serum samples were collected at slaughter from 226 24-30-month-old American bison (Bison bison) bulls from Kansas, Minnesota, North Dakota, and Manitoba and assayed for antibodies to ovine herpesvirus type-2 (OHV-2), bovine viral diarrhea virus (BVDV), bovine herpesvirus type-1 (BHV-1), and bovine respiratory syncytial virus (BRSV). Antibodies were detected by serum neutralization for BVDV, BHV-1, and BRSV, while antibodies to OHV-2 were detected by competitive inhibition-ELISA (CI-ELISA). Detectable antibodies were found against all viruses: 10 of 226 (4.40%) against OHV-2, 125 of 226 (55.3%) against BVDV, 99 of 226 (43.8%) against BHV-1, and 208 of 226 (92.0%) against BRSV. Titers from 93.6% of the BVDV-positive animals, 79.8% of the BHV-1-positive animals, and 98.1% of the BRSV-positive animals were > or = 1.25. These data indicate that a low percentage of clinically normal bison are seropositive for OHV-2 while a high percentage of bison sampled are seropositive for BVDV, BHV-1, and BRSV.     

Epizootic malignant catarrhal fever in three bison herds: differences from cattle and association with ovine herpesvirus-2.

Three bison herds in Colorado experienced high mortality from malignant catarrhal fever (MCF). In comparison with cattle, the bison had a more rapidly progressive disease, fewer clinical signs, and milder inflammatory histologic lesions. There was consistent association with ovine herpesvirus-2 (OHV-2). Contact with sheep was not consistent. Of 17 animals in herd A, 15 died of acute MCF; 1 was slaughtered while healthy; and 1 developed clinical signs of MCF, was treated with corticosteroids and antibiotics, and died of fungal abomasitis and rhinitis after 5 months. In herds B and C, approximately 300 of 900 and 18 of 20 died of MCF following brief clinical disease. The nearest sheep were 1 mile away from herd A, but direct contact with sheep could be documented in herds B and C. Complete gross and histologic examinations were conducted on 34 animals, including all animals in herd A, and MCF was diagnosed in 31. In addition, field necropsies were performed on all dead animals in herd B and most in herd C and MCF was diagnosed on the basis of the gross lesions in most animals. Clinical signs of each animal in herd A were recorded. Illness was brief, usually 8-48 hours. Clinical signs were subtle; separation from the herd was often observed. In all 3 herds, hemorrhagic cystitis and multifocal ulceration of the alimentary tract were consistently found at necropsy. Mild lymphocytic vasculitis was present in multiple organs. Ovine herpesvirus-2 was found by polymerase chain reaction (PCR) in 71 of 105 formalin-fixed tissue specimens from 29 of 31 animals with MCF. In herd A, blood samples from 13 animals were collected at 5 time points and tested by PCR for the presence of OHV-2 viral sequences in peripheral blood leukocytes. Nine bison with a positive PCR test and 4 with negative results prior to clinical illness died of MCF.     

Pasteurellaceae isolated from tonsillar samples of commercially-reared American bison (Bison bison).

As commercial producers of American bison (Bison bison) become more numerous, concerns relative to bison health management increase. Since loss due to respiratory disease associated with Pasteurella and related Pasteurellaceae is a major concern for cattle producers, a study was conducted to determine what types of Pasteurellaceae are carried by bison to evaluate the potential of pneumonic pasteurellosis in bison herds where management practices are comparable to those used for cattle. Tonsillar biopsies, collected in May (n = 29) and August (n = 25) 1997 from 24- to 30-month-old bison bulls, at the time of slaughter were cultured for Pasteurellaceae. Pasteurella spp. were isolated from all the samples collected in May. These included isolates identified as P. haemolytica, trehalosi, testudinis, and multocida subsp. multocida a and multocida b. Actinobacillus spp. and Haemophilus somnus were also isolated from some samples. Pasteurella spp., haemolytica, trehalosi, and multocida subsp. multocida a, multocida b and septica, plus 2 nonspeciated indole-positive biotypes, U2 and U16, were isolated from the second group of tonsil samples. Most of these organisms, including P. haemolytica, P. multocida subsp., and H. somnus are associated with disease in domestic livestock and should be regarded as potential pathogens for bison, particularly in animals which become stressed by management practices commonly used with cattle such as herding, crowding, and shipping.     

Anaplasma marginale infections in American bison: experimental infection and serologic study

Anaplasma marginale was experimentally transmitted from cattle to bison and back to cattle. Of the 2 splenectomized and 1 intact American bison calves (Bison bison) inoculated with a North Texas A marginale stabilate, 1 splenectomized and 1 intact bison exhibited clinical signs of anaplasmosis. Active parasitemias in these bison were observed along with positive reactions in the rapid card agglutination and complement fixation tests. Blood from the infected bison produced disease in splenectomized bovine calves. Screening tests for anti-Anaplasma antibodies in 178 blood samples collected from adult bison from the National Bison Range, Montana, revealed 1 rapid card agglutination test-positive sample, and 110 negative, 40 suspect, and 28 positive (15.7%) complement fixation test samples.     

Malignant catarrhal fever in a bison (Bison bison) feedlot, 1993-2000.

A fatal enteric syndrome was identified in American bison (Bison bison) at a large feedlot in the American Midwest in early 1998. An estimated 150 bison died of the syndrome between January 1998 and December 1999. The syndrome was identified as malignant catarrhal fever (MCF), primarily the alimentary form. Clinical onset was acute, and most affected bison died within 1-3 days; none recovered. Consistent lesions were hemorrhagic cystitis, ulcerative enterotyphlocolitis, and arteritis-phlebitis. Vasculitis was milder and more localized than that in cattle with MCF, and in contrast to the situation in cattle, lymphadenomegaly was minimal. Virtually all affected bison examined were positive for ovine herpesvirus 2 (OvHV-2) by polymerase chain reaction (PCR) assay. A retrospective study of archived tissues established that MCF occurred in the yard as early as 1993. A prospective study was undertaken to establish the importance of MCF relative to other fatal diseases at the feedlot. The fate of a group of 300 healthy male bison in a consignment of 1,101 animals was followed for up to 7 months to slaughter. At entry, 23% (71/300) of bison were seropositive for MCF viruses, and 11% (8/71) of these seropositive bison were PCR positive for OvHV-2. Forty seronegative bison were selected at random from the group, and all were PCR negative for OvHV-2. There was no change in seroprevalence in the group during the investigation. The minimum infection rate for MCF virus was 36.3% (93/256). Twenty-two (7.3%) of the 300 bison in the feedlot died. Of these, 15 had MCF, 4 had acute or chronic pneumonia, and 3 were unexamined. Losses in the entire consignment were higher (98/1,101; 8.8% death loss); 76% of deaths were attributable to MCF. The study failed to reveal a relationship between subclinical infection and development of clinical disease.     

Intra-nasal inoculation of American bison (Bison bison) with ovine herpesvirus-2 (OvHV-2) reliably reproduces malignant catarrhal fever

Sheep-associated malignant catarrhal fever (MCF) due to infection with ovine herpesvirus 2 (OvHV-2) is common in commercial herds of American bison ( Bison bison). Inability to propagate OvHV-2 in vitro has been a constraint on experimental studies of the disease. We sought to establish whether nasal secretions from sheep that shed OvHV-2 might induce the disease in bison and to define a minimum challenge dose. Fourteen bison were nebulized with sheep nasal sections containing 10(3)-10(7) OvHV-2 deoxyribonucleic acid (DNA) copies. Most challenged bison (11/14, 78.6%) developed clinical signs at 29-52 days postnebulization (DPN). The mean incubation time was 42.18 (+/-7.33 SD) DPN. Using real-time polymerase chain reaction, we detected OvHV-2 DNA in peripheral blood leukocytes at 21-31 DPN. All bison that developed MCF had antibodies against the MCF group viruses. Gross and histologic lesions were typical of the acute disease. There was no morphologic evidence of a dose-related difference in the severity or distribution of lesions. This is the first successful reproduction of MCF in bison using a nasal route of exposure. Experimentally challenged bison are more susceptible to MCF, compared with experimentally challenged domestic cattle in a previous experiment. Bison are a pertinent ruminant species in which the pathogenesis of the disease can be investigated.     

Comparative blood characteristics of ranched and free-ranging American bison (Bison bison)

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 less than 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 less than 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.     

Recovery and Cryopreservation of Epididymal Sperm of Plains Bison (Bison bison bison) as a Model for Salvaging the Genetics of Wood Bison (Bison bison athabascae)

The objective of this study was to optimize recovery and cryopreservation of epididymal sperm from plains bison, as a model for wood bison. In Phase 1, cauda epididymides were recovered from bison (n = 14) immediately after slaughter, minced and incubated in Sp-TALPH buffer for 3 h at 36°C. The resulting sperm suspensions were cryopreserved in Triladyl^®, using a protocol for bovine semen. In Phase 2, epididymal sperm were cryopreserved in either Triladyl^® or Andromed^®. The mean (±SD) estimated number of sperm recovered was 468 ± 207 × 10⁶. There was an increase (p < 0.05) in the proportion of sperm with normal morphology between initial recovery and after extension (52.4 ± 4.6 vs 69.7 ± 2.4%), with a concurrent decrease (p < 0.05) in the proportion of sperm with distal droplets. Median values for progressively motile sperm in post-thaw samples (60%) were lower (p < 0.05) than that after extension or after chilling (70% for both). The mean percentages of viable sperm and of sperm with an intact acrosome were lower (p < 0.05) for frozen-thawed samples (38.7 ± 2.8 and 85.2 ± 1.1) compared with extended (66.2 ± 2.2 and 92.4 ± 0.9) or chilled (63.7 ± 2.5 and 90.0 ± 1.0) samples. Rates of cleavage, morulae and blastocyst production were not significantly different for chilled (70.9, 38.7 and 8.0%) vs post-thaw sperm (73.0, 46.0 and 6.3%). There was no significant difference between extenders for most sperm characteristics. In conclusion, we developed a functional protocol for the recovery and cryopreservation of epididymal sperm from plains bison, which may have implications for the genetic preservation of wood bison.     

A survey to detect Toxocara vitulorum and other gastrointestinal parasites in bison (Bison bison) herds from Manitoba and Saskatchewan

An egg count survey using environmental fecal samples obtained in spring or early summer was conducted to estimate the apparent prevalence of Toxocara vitulorum in unweaned bison calves and of other intestinal parasites in adult bison on 98 farms in Manitoba and Saskatchewan. Calf samples were pooled (maximum 5 samples per pool) by farm and positive pools were examined to determine individual T. vitulorum counts. Toxocara vitulorum eggs were found on 4 farms in Manitoba and none in Saskatchewan. Apparent herd-level prevalence estimates were 12% [95% confidence interval (95% CI): 3.4% to 28.2%] and 0% (95% CI: 0% to 5.7%) respectively. Samples from adult bison contained eggs/oocysts from trichostrongyle species, Eimeria sp., Monieza sp., Capillaria sp., Nematodirus sp. and Trichuris sp. in 100%, 95%, 72%, 13%, 13%, and 5% of herds, respectively. Strongyloides sp. were not found in any herd. Further studies are needed to assess parasite distribution patterns in bison and to evaluate the risk that T. vitulorum may pose to bison, cattle, and wildlife.     

The pathology of spontaneous paratuberculosis in the North American bison (Bison bison)

Gross and histopathologic examinations were performed on 70 North American bison (Bison bison) from a Mycobacterium avium paratuberculosis culture-positive herd. The bison examined were part of a breeding herd totaling 2,800 animals. Eight of 70 (11%) animals had gross findings of intestinal mucosal thickening, and 16 of 70 (23%) of the animals had enlarged mesenteric lymph nodes. Histologic lesions compatible with Johne's disease were diagnosed in 30 of 70 (43%) bison on the basis of the demonstration of noncaseating granulomatous inflammatory infiltrates and of one or more acid-fast bacilli characteristic of Mycobacterium avium paratuberculosis. A suspicious diagnosis of Johne's disease was obtained in 11 of 70 (16%) bison on the basis of the observation of noncaseating granulomatous inflammatory infiltrates without demonstrable acid-fast bacteria. Twenty-nine of 70 (41%) animals were assessed as histologically paratuberculosis free. Histologic results were compared to Johne's disease tests such as culture, serology, and polymerase chain reaction, which were performed on some of the cohort animals.     

Seasonal incidence and antibiotic susceptibility patterns of Pasteurellaceae isolated from American bison (Bison bison).

Ninety pharyngeal tonsils were collected from 2-year-old American bison (Bison bison) bulls and sampled for members of the Pasteurellaceae family. Particular attention was paid to seasonal incidence and antimicrobial resistance in serotypes and biovariants. Multiple strains of Pasteurella haemolytica (39%), P. trehalosi (68%), P. multocida (34%) and Haemophilus somnus (13%) were cultured from 86 out of the 90 (96%) tonsil samples. Pasteurella trehalosi was the most common and evenly distributed of the organisms recovered. Pasteurella haemolytica was found in fewer numbers than P. trehalosi, but showed an increase in number of isolates recovered with each sampling period. Pasteurella multocida, both A and D capsular types, was recovered from all sampling periods. No serotype pattern was observed in any of the animal groups sampled. One hundred twenty-seven of 147 (86%) of the isolates were resistant to at least 1 antibiotic, 95/147 (65%) to at least 2 different antibiotics, and 16/147 (11%) to at least 3 antibiotics. The most common resistance pattern observed was to neomycin and spectinomycin (73/147) (49%).     

Pathogenesis of Mycobacterium bovis infection in American bison

Eighteen 12-month-old bison were randomly placed in each of 3 groups (6 animals/group): group-1 bison were exposed to live Mycobacterium bovis, group-2 bison were inoculated with killed M bovis in oil, and group-3 bison were noninfected controls. Six, 6-month-old, tuberculin test-negative calves were placed (pen contact) with group-1 bison 30 days after exposure to M bovis. Tuberculin skin test responses (caudal fold and/or comparative cervical) were detected in all bison in groups 1 and 2 at 2, 4, 6, 10, and 12 months. Tuberculin skin test responses were observed in 2 of 6 calves at 9 and 11 months after pen contact with M bovis-exposed bison (group 1). Statistically significant lymphocyte blastogenic responses to M bovis purified protein derivative were detected in group-1 bison exposed to live M bovis at 2 months after exposure (P less than 0.025). Significant ELISA reactions were detected in sera of bison at 2 months after exposure to killed M bovis in oil (P less than 0.005) and in bison 2 months after exposure to live M bovis (P less than 0.01). Significant tuberculin skin responses, ELISA reactions, or lymphocyte blastogenic responses to M bovis purified protein derivative were not observed in the 6 control bison. Grossly visible tuberculous lesions were observed in lymph nodes and/or lung collected at necropsy in 4 of 6 bison at 12 months after exposure to live M bovis. Microscopic granulomas compatible with tuberculosis were detected in 5 of 6 bison; M bovis was isolated from tissues of each of the 6 bison.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical Parelaphostrongylus tenuis infection in two captive American bison (Bison bison)

CASE DESCRIPTION: 2 juvenile (17 and 19 months of age) male American bison (Bison bison) were examined because of acute bilateral hind limb weakness and ataxia; 1 animal also had urinary incontinence. TREATMENT AND OUTCOME: Given the clinical signs and rapid deterioration in the condition of these 2 animals, obtaining a definitive diagnosis was considered essential to minimizing the risk of disease in the remaining bison herd and among other animals at the facility. Therefore, both affected animals were euthanized. At necropsy, no gross abnormalities were seen. Histologic examination of sections of the brains from both animals revealed mild to moderate multifocal aggregates of eosinophils and mononuclear cells in perivascular regions of the meninges and gray matter of the cerebrum, cerebellum, and brainstem. Systematic examination of multiple sections of brain and spinal cord revealed evidence of nematode sections and aberrant parasite migration. CLINICAL RELEVANCE: Findings suggested that CNS migration of Parelaphostrongylus tenuis in American bison may cause clinical signs. These findings have implications for the management of captive bison and free-ranging bison sharing ranges with white-tailed deer (Odocoileus virginianus), the definitive host, and elk (Cervus elaphus canadensis).     

Haemophilus somnus bronchopneumonia in American bison (Bison bison).

Immunoperoxidase assays were performed on 21 archived formalin-fixed, paraffin-embedded tissues from from American bison (Bison bison) with bronchopneumonia. Seven of the 21 bison had positive staining for Haemophilus somnus in alveolar exudate, visceral pleura, lung parenchyma, and chronic necrotic lesions, and H. somnus was isolated from tissues from 1 of these 7 animals. Results suggest that H. somnus is a respiratory pathogen in bison.     

Characterization of putative Haemophilus somnus isolates from tonsils of American bison (Bison bison).

Three Haemophilus somnus isolates (2a, 3a, and 27b) and one H. somnus-like (13b) isolate from tonsils of commercially reared American bison were compared with 2 known H. somnus isolates from cattle, namely, 2336, shown to cause respiratory disease, and 129Pt, from the prepuce of an asymptomatic bull. All H. somnus isolates, but not the H. somnus-like isolate, required CO2 for growth. Biochemical utilization profiles were identical for bison and bovine H. somnus isolates with the exception of alpha-fucosidase production by isolate 3a. Isolate 27a varied from 2a, 2336 and 129Pt by hemolysis of bovine erythrocytes. Isolate 13b hemolyzed sheep but not bovine or bison erythrocytes and varied from other isolates in biochemical utilization tests. Outer membrane protein profiles of 2a, 3a and 27a were almost identical with those of bovine isolate 2336 and similar to that of 129Pt, but quite different from that of 13b. Western blots of bison isolates were similar to that of the virulent bovine 2336 isolate, including detection of high molecular mass antigens above 100 kDa and the 76 kDa antigens associated with bovine IgG2 Fc binding characteristic of virulent strains, as well as antigens of approximately 78, 60 and 40 kDa. Producers and veterinarians should be aware that H. somnus may be carried by bison and may have potential for causing diseases in bison similar to those described in cattle and sheep.     

Mycotic rumenitis in American bison (Bison bison).

Necropsies were performed on 2 American bison (Bison bison) cows, I of which died acutely and the other that died after a week of illness. Gross and microscopic lesions were consistent with severe mycotic infection of the forestomachs. Both animals had been abruptly placed on a breeder ration 1 month after calving, and had developed acidosis and subsequent fungal invasion of tissues. History and lesions in this case indicate that bison are susceptible to rumen acidosis and its sequelae.     

Efficacy of calfhood vaccination with Brucella abortus strain RB51 in protecting bison against brucellosis

In the studies reported here, protection induced by calfhood vaccination of bison with 1.2-6.1 x 10(10)CFU of Brucella abortus strain RB51 (SRB51) against a virulent strain of B. abortus was evaluated. Non-vaccinated and SRB51-vaccinated bison were intraconjunctivally challenged during midgestation with 3 x 10(7)CFU of virulent B. abortus strain 2308 (S2308). Maternal and fetal tissues were obtained within 24hour after abortion or parturition. Incidence of abortion was greater (P<0.05) in non-vaccinated as compared to SRB51-vaccinated bison (62% and 15%, respectively), with abortions occurring between 5 and 8 weeks after experimental challenge. Calves from bison vaccinated with SRB51 had a reduced (P<0.05) prevalence of fetal infection with S2308 as compared to calves from non-vaccinated bison (19% and 62%, respectively). Although the ability to recover the 2308 challenge strain from maternal tissues did not differ (P>0.05) between nonvaccinates and vaccinates (100% and 78%, respectively), calfhood vaccination with SRB51 reduced (P<0.05) recovery of S2308 from uterine or mammary gland tissues. In bison which did not abort, S2308 was routinely recovered in low numbers from maternal lymphatic tissues; particularly the parotid, bronchial, supramammary, and mandibular lymph nodes. The RB51 vaccine strain was not recovered at any time from maternal or fetal samples obtained at necropsy. Histological lesions associated with Brucella-induced abortions were suppurative placentitis, fetal broncho-interstitial pneumonia, and fetal histiocytic splenitis. The results of our studies suggest that calfhood vaccination of bison with SRB51 is efficacious in protecting against intramammary, intrauterine, and fetal infection following exposure to a virulent strain of B. abortus during pregnancy. As brucellosis is transmitted horizontally through fluids associated with the birth or abortion of an infected fetus, or vertically to the calf through the ingestion of milk containing B. abortus, our data suggest that calfhood vaccination with SRB51 will be beneficial in preventing transmission of brucellosis in bison.     

Effect of Chilling Duration on Post‐Thaw Characteristics of Sperm from the North American bison (Bison bison)

The objective of this study was to determine the duration for which sperm from the North American bison (Bison bison) could be chilled prior to being cryopreserved, without compromising post‐ thaw sperm quality. This would permit transport of samples collected remotely, to the laboratory (at 4°C) for cryopreservation. Epididymal sperm from plains bison (n = 11) and ejaculated sperm from wood bison (n = 3) were collected, extended and held at 4°C for extended periods of time. At intervals, an aliquot was cryopreserved. Post‐thaw sperm motion characteristics were evaluated by computer assisted sperm analysis. Representative plains bison sperm samples (n = 3) were evaluated for their in vitro fertilizing ability in a heterologous system using bovine oocytes. There was no statistical difference in total and progressive motility of plains bison epididymal sperm when cryopreserved after chilling for 24, 48 or 72 h. For wood bison ejaculated sperm, there was no difference in total and progressive motility for sperm cryopreserved following 24 or 48 h of chilling. However, one of the three bulls showed significantly poorer fertilization (based on cleavage rate) with sperm chilled for 72 compared to 24 and 48 h prior to freezing. In conclusion, plains bison epididymal sperm can be chilled for 72 h and wood bison ejaculated sperm can be chilled for at least 48 h prior to cryopreservation without compromising post‐thaw sperm motility, while heterologous in vitro fertilization (IVF) assay indicated a between‐bull variation in the in vitro fertilizing ability of sperm chilled for an extended duration before cryopreservation.     

Breeding soundness examination of North American bison bulls

OBJECTIVE: To evaluate the breeding soundness examination procedure in plains bison bulls. DESIGN: Multiyear (1993 through 1997) cross-sectional clinical procedure evaluation. ANIMALS: Two hundred thirty-four 28- to 30-month-old bison bulls at Custer State Park. PROCEDURE: Breeding soundness examinations were performed on all bison bulls using 1992 Society for Theriogenology guidelines for beef cattle semen evaluation and reproductive tract examination. Linear and logistic regression analyses were used to detect correlations and associations among breeding soundness examination variables. RESULTS: Scrotal circumference (SC) was significantly correlated with body weight, percentage of normal spermatozoa, percentage of primary spermatozoal defects, and percentage of motile spermatozoa. Scrotal circumference was positively associated with increased odds of semen collection, satisfactory motility (> or = 30% motility), satisfactory morphology (> or = 70% normal spermatozoa), and simultaneous satisfactory motility and morphology. Receiver-operator characteristic curve analysis selected 29 cm as the optimal SC cutoff most predictive of simultaneous satisfactory spermatozoal motility and morphology. Only 36.2% (83/229) of the bison bulls had a SC of 29 cm or greater and satisfactory spermatozoal motility and morphology. CLINICAL IMPLICATIONS: SC is a good indicator of adequate spermatozoal motility and structure in bison. We recommend use of 30% spermatozoal motility, 70% normal spermatozoal morphology, and 29-cm SC as minimal satisfactory measurements for breeding soundness examinations of 28- to 30-month-old bison bulls that have been raised on forage-based nutrition.     

Effect of Reproductive Seasonality on Gamete Quality in the North American Bison (Bison bison bison)

The objective was to investigate the effects of reproductive seasonality on gamete quality in plains bison (Bison bison bison). Epididymal sperm (n = 61 per season), collected during the breeding season (July–September), had significantly higher post‐thaw total motility (36.76 ± 14.18 vs 31.24 ± 12.74%), and lower linearity (0.36 ± 0.06 vs 0.39 ± 0.04) and wobbliness (0.49 ± 0.04 vs 0.51 ± 0.03; mean ± SD) compared to non‐breeding season (January–March) samples. Representative samples (n = 4) from each season were used in heterologous IVF trials using cattle oocytes. Cleavage, morulae and blastocyst percentage were higher for breeding vs non‐breeding season sperm samples (81.88 ± 6.8 vs 49.94 ± 6.77; 41.89 ± 13.40 vs 27.08 ± 23.21; and 30.49 ± 17.87 vs 13.72 ± 18.98%, respectively). Plains bison ovaries collected during the breeding (n = 97 pairs) and non‐breeding (n = 100 pairs) seasons were classified as luteal or follicular. Oocytes recovered from these ovaries were classified into five grades based on morphology. There was no significant difference in the number of luteal ovaries or grades of oocytes recovered. Oocytes were matured, fertilized (with frozen sperm from three bison bulls) and cultured in vitro. Cleavage percentage was higher for oocytes collected during breeding vs non‐breeding season (83.72 ± 6.42 vs 73.98 ± 6.43), with no significant difference in subsequent development to blastocysts. In summary, epididymal sperm from non‐breeding season had decreased total motility and resulted in reduced embryo production in vitro. Oocytes collected during non‐breeding season had reduced ability to be matured, fertilized and/or undergo cleavage in vitro. Data suggested that season influenced gamete quality in plains bison.