American bison Bison bison

American bison are a native North American wild bovid now farmed at modest scale: the 2022 US Census of Agriculture recorded 192,477 bison on 1,986 operations, averaging 137 head, and Alberta alone carries more than 440 producing farms. Two-thirds of US operations (67.9 percent) run cow-calf herds, 40.5 percent finish on grass and about a third keep bison as hobby animals or for conservation; 93.7 percent graze range or pasture. Bulls weigh 600 to 860 kg and cows 350 to 550 kg. Breeding is tightly seasonal: rut from June to October peaking in early August, calving April to June after a gestation of 262 to 300 days, first calving usually at three years, and most US operations first breeding heifers at 24 to 30 months. Bison live about 15 years in the wild and beyond 20 in captivity. The veterinary reality is that bison are handled rather than examined - only 69.3 percent of operations have restraint facilities at all - so herd-level medicine dominates. Internal parasites are the commonest reported problem, on 22.5 percent of operations, followed by weight loss and diarrhoea. Mycoplasma bovis behaves as a primary pathogen causing severe pneumonia, pleuritis and polyarthritis; sheep-associated malignant catarrhal fever is fatal in bison; and wild bison in the Greater Yellowstone Area remain the last US brucellosis reservoir.