Ruminant

From Wikipedia, the free encyclopedia

Stylised illustration of a ruminant digestive system

 

Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again". 

 

The roughly 200 species of living ruminants include both domestic and wild species. Ruminating mammals include cattle, all domesticated and wild bovines, goats, sheep, giraffes, deer, gazelles, and antelopes. It has also been suggested that notoungulates also relied on rumination, as opposed to other atlantogenates that rely on the more typical hindgut fermentation, though this is not entirely certain.

Taxonomically, the suborder Ruminantia (also known as ruminants) is a lineage of herbivorous artiodactyls that includes the most advanced and widespread of the world's ungulates. The term 'ruminant' is not synonymous with Ruminantia. The suborder Ruminantia includes many ruminant species, but does not include tylopods and marsupials. The suborder Ruminantia includes six different families: Tragulidae, Giraffidae, Antilocapridae, Moschidae, Cervidae, and Bovidae.

Description

Different forms of the stomach in mammals. A, dog; B, Mus decumanus; C, Mus musculus; D, weasel; E, scheme of the ruminant stomach, the arrow with the dotted line showing the course taken by the food; F, human stomach. a, minor curvature; b, major curvature; c, cardiac end G, camel; H, Echidna aculeata. Cma, major curvature; Cmi, minor curvature. I, Bradypus tridactylus Du, duodenum; MB, coecal diverticulum; **, outgrowths of duodenum; †, reticulum; ††, rumen. A (in E and G), abomasum; Ca, cardiac division; O, psalterium; Oe, oesophagus; P, pylorus; R (to the right in E and to the left in G), rumen; R (to the left in E and to the right in G), reticulum; Sc, cardiac division; Sp, pyloric division; WZ, water-cells. (from Wiedersheim's Comparative Anatomy)

 

Food digestion in the simple stomach of nonruminant animals versus ruminants

 

The primary difference between ruminants and nonruminants is that ruminants' stomachs have four compartments:

1. rumen—primary site of microbial fermentation
2. reticulum
3. omasum—receives chewed cud, and absorbs volatile fatty acids
4. abomasum—true stomach

The first two chambers are the rumen and the reticulum. These two compartments make up the fermentation vat, they are the major site of microbial activity. Fermentation is crucial to digestion because it breaks down complex carbohydrates, such as cellulose, and enables the animal to utilize them. Microbes function best in a warm, moist, anaerobic environment with a temperature range of 37.7 to 42.2 °C (100 to 108 °F) and a pH between 6.0 and 6.4. Without the help of microbes, ruminants would not be able to utilize nutrients from forages. The food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud or bolus.

The cud is then regurgitated and chewed to completely mix it with saliva and to break down the particle size. Smaller particle size allows for increased nutrient absorption. Fiber, especially cellulose and hemicellulose, is primarily broken down in these chambers by microbes (mostly bacteria, as well as some protozoa, fungi, and yeast) into the three volatile fatty acids (VFAs): acetic acid, propionic acid, and butyric acid. Protein and nonstructural carbohydrate (pectin, sugars, and starches) are also fermented. Saliva is very important because it provides liquid for the microbial population, recirculates nitrogen and minerals, and acts as a buffer for the rumen pH. The type of feed the animal consumes affects the amount of saliva that is produced. 

Though the rumen and reticulum have different names, they have very similar tissue layers and textures, making it difficult to visually separate them. They also perform similar tasks. Together, these chambers are called the reticulorumen. The degraded digesta, which is now in the lower liquid part of the reticulorumen, then passes into the next chamber, the omasum. This chamber controls what is able to pass into the abomasum. It keeps the particle size as small as possible in order to pass into the abomasum. The omasum also absorbs volatile fatty acids and ammonia.

After this, the digesta is moved to the true stomach, the abomasum. This is the gastric compartment of the ruminant stomach. The abomasum is the direct equivalent of the monogastric stomach, and digesta is digested here in much the same way. This compartment releases acids and enzymes that further digest the material passing through. This is also where the ruminant digests the microbes produced in the rumen. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. The small intestine is the main site of nutrient absorption. The surface area of the digesta is greatly increased here because of the villi that are in the small intestine. This increased surface area allows for greater nutrient absorption. Microbes produced in the reticulorumen are also digested in the small intestine. After the small intestine is the large intestine. The major roles here are breaking down mainly fiber by fermentation with microbes, absorption of water (ions and minerals) and other fermented products, and also expelling waste. Fermentation continues in the large intestine in the same way as in the reticulorumen. 

Only small amounts of glucose are absorbed from dietary carbohydrates. Most dietary carbohydrates are fermented into VFAs in the rumen. The glucose needed as energy for the brain and for lactose and milk fat in milk production, as well as other uses, comes from nonsugar sources, such as the VFA propionate, glycerol, lactate, and protein. The VFA propionate is used for around 70% of the glucose and glycogen produced and protein for another 20% (50% under starvation conditions).

Classification and taxonomy

Hofmann and Stewart divided ruminants into three major categories based on their feed type and feeding habits: concentrate selectors, intermediate types, and grass/roughage eaters, with the assumption that feeding habits in ruminants cause morphological differences in their digestive systems, including salivary glands, rumen size, and rumen papillae. However, Woodall found that there is little correlation between the fiber content of a ruminant's diet and morphological characteristics, meaning that the categorical divisions of ruminants by Hofmann and Stewart warrant further research.

Also, some mammals are pseudoruminants, which have a three-compartment stomach instead of four like ruminants. The Hippopotamidae (comprising hippopotami) are well-known examples. Pseudoruminants, like traditional ruminants, are foregut fermentors and most ruminate or chew cud. However, their anatomy and method of digestion differs significantly from that of a four-chambered ruminant.

Monogastric herbivores, such as rhinoceroses, horses, and rabbits, are not ruminants, as they have a simple single-chambered stomach. These hindgut fermenters digest cellulose in an enlarged cecum through the reingestion of the cecotrope.

Abundance, distribution, and domestication

Wild ruminants number at least 75 million and are native to all continents except Antarctica. Nearly 90% of all species are found in Eurasia and Africa. Species inhabit a wide range of climates (from tropic to arctic) and habitats (from open plains to forests).

The population of domestic ruminants is greater than 3.5 billion, with cattle, sheep, and goats accounting for about 95% of the total population. Goats were domesticated in the Near East circa 8000 BC. Most other species were domesticated by 2500 BC., either in the Near East or southern Asia.

Ruminant physiology

Ruminating animals have various physiological features that enable them to survive in nature. One feature of ruminants is their continuously growing teeth. During grazing, the silica content in forage causes abrasion of the teeth. This abrasion is compensated for by continuous tooth growth throughout the ruminant's life, as opposed to humans or other nonruminants, whose teeth stop growing after a particular age. Most ruminants do not have upper incisors; instead, they have a thick dental pad to thoroughly chew plant-based food. Another feature of ruminants is the large ruminal storage capacity that gives them the ability to consume feed rapidly and complete the chewing process later. This is known as rumination, which consists of the regurgitation of feed, rechewing, resalivation, and reswallowing. Rumination reduces particle size, which enhances microbial function and allows the digesta to pass more easily through the digestive tract.

Rumen microbiology

Vertebrates lack the ability to hydrolyse the beta [1–4] glycosidic bond of plant cellulose due to the lack of the enzyme cellulase. Thus, ruminants must completely depend on the microbial flora, present in the rumen or hindgut, to digest cellulose. Digestion of food in the rumen is primarily carried out by the rumen microflora, which contains dense populations of several species of bacteria, protozoa, sometimes yeasts and other fungi – 1 ml of rumen is estimated to contain 10–50 billion bacteria and 1 million protozoa, as well as several yeasts and fungi.

Since the environment inside a rumen is anaerobic, most of these microbial species are obligate or facultative anaerobes that can decompose complex plant material, such as cellulose, hemicellulose, starch, and proteins. The hydrolysis of cellulose results in sugars, which are further fermented to acetate, lactate, propionate, butyrate, carbon dioxide, and methane.

As bacteria conduct fermentation in the rumen, they consume about 10% of the carbon, 60% of the phosphorus, and 80% of the nitrogen that the ruminant ingests. To reclaim these nutrients, the ruminant then digests the bacteria in the abomasum. The enzyme lysozyme has adapted to facilitate digestion of bacteria in the ruminant abomasum. Pancreatic ribonuclease also degrades bacterial RNA in the ruminant small intestine as a source of nitrogen.

During grazing, ruminants produce large amounts of saliva – estimates range from 100 to 150 litres of saliva per day for a cow. The role of saliva is to provide ample fluid for rumen fermentation and to act as a buffering agent. Rumen fermentation produces large amounts of organic acids, thus maintaining the appropriate pH of rumen fluids is a critical factor in rumen fermentation. After digesta pass through the rumen, the omasum absorbs excess fluid so that digestive enzymes and acid in the abomasum are not diluted.

Tannin toxicity in ruminant animals

Tannins are phenolic compounds that are commonly found in plants. Found in the leaf, bud, seed, root, and stem tissues, tannins are widely distributed in many different species of plants. Tannins are separated into two classes: hydrolysable tannins and condensed tannins. Depending on their concentration and nature, either class can have adverse or beneficial effects. Tannins can be beneficial, having been shown to increase milk production, wool growth, ovulation rate, and lambing percentage, as well as reducing bloat risk and reducing internal parasite burdens.

Tannins can be toxic to ruminants, in that they precipitate proteins, making them unavailable for digestion, and they inhibit the absorption of nutrients by reducing the populations of proteolytic rumen bacteria. Very high levels of tannin intake can produce toxicity that can even cause death. Animals that normally consume tannin-rich plants can develop defensive mechanisms against tannins, such as the strategic deployment of lipids and extracellular polysaccharides that have a high affinity to binding to tannins. Some ruminants (goats, deer, elk, moose) are able to consume feed high in tannins (leaves, twigs, bark) due to the presence in their saliva of tannin-binding proteins.

Religious importance

The Law of Moses in the Bible only allowed the eating of mammals that had cloven hooves (i.e. members of the order Artiodactyla) and "that chew the cud", a stipulation preserved to this day in Jewish dietary laws.

Other uses

The verb 'to ruminate' has been extended metaphorically to mean to ponder thoughtfully or to meditate on some topic. Similarly, ideas may be 'chewed on' or 'digested'. 'Chew the (one's) cud' is to reflect or meditate. In psychology, "rumination" refers to a pattern of thinking, and is unrelated to digestive physiology.

Ruminants and climate change

Methane is produced by a type of archaea, called methanogens, as described above within the rumen, and this methane is released to the atmosphere. The rumen is the major site of methane production in ruminants. Methane is a strong greenhouse gas with a global warming potential of 86 compared to CO₂ over a 20-year period.

In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world, 26% of the total greenhouse gas emissions from agricultural activity in the U.S., and 22% of the total U.S. methane emissions. The meat from domestically-raised ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies. Methane production by meat animals, principally ruminants, is estimated 15–20% global production of methane, unless the animals were hunted in the wild. However, the current U.S. domestic beef and dairy cattle population is around 90 million head, which is not much different from the peak wild population of American Bison that primarily roamed the part of North America that now makes up the U.S. This is estimated to have been over 60 million head in the 1700s and prior. In addition, EPA estimates suggest bison produce more methane per head than cattle, with modern feedlot beef cattle producing perhaps as low as half the methane of bison per head. Therefore, it is likely that the pre-industrialized North American wild bison herd released more total methane into the atmosphere than the current total domesticated herd of beef and dairy cattle.

Bison

From Wikipedia, the free encyclopedia

Bison Temporal range: 2–0 Ma PreЄ Є O S D C P T J K Pg N ↓ Early Pleistocene – Recent
American bison (Bison bison)
European bison (Bison bonasus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	Bovidae
Subfamily:	Bovinae
Subtribe:	Bovina
Genus:	Bison Hamilton Smith, 1827
Species
B. bison B. bonasus †B. antiquus †B. georgicus †B. hanaizumiensis †B. latifrons †B. menneri †B. occidentalis †B. palaeosinensis †B. priscus †B. schoetensacki

Bison are large, even-toed ungulates in the genus Bison within the subfamily Bovinae.

Two extant and six extinct species are recognised. Of the six extinct species, five became extinct in the Quaternary extinction event. Bison palaeosinensis evolved in the Early Pleistocene in South Asia, and was the evolutionary ancestor of B. priscus (steppe bison), which was the ancestor of all other Bison species. From 2 MYA to 6,000 BC, steppe bison ranged across the mammoth steppe, inhabiting Europe and northern Asia with B. schoetensacki (woodland bison), and North America with B. antiquus, B. latifrons, and B. occidentalis. The last species to go extinct, B. occidentalis, was succeeded at 3,000 BC by B. bison.

Of the two surviving species, the American bison, B. bison, found only in North America, is the more numerous. Although commonly known as a buffalo in the United States and Canada, it is only distantly related to the true buffalo. The North American species is composed of two subspecies, the Plains bison, B. b. bison, and the Wood bison, B. b. athabascae, which is the namesake of Wood Buffalo National Park in Canada. A third subspecies, the Eastern Bison (B. b. pennsylvanicus) is no longer considered a valid taxon, being a junior synonym of B. b. bison. References to "Woods Bison" or "Wood Bison" from the eastern United States confusingly refer to this subspecies, not B. b. athabascae, which was not found in the region. The European bison, B. bonasus, or wisent, is found in Europe and the Caucasus, reintroduced after being extinct in the wild.

While all bison species are classified in their own genus, they are sometimes bred with domestic cattle (genus Bos) and produce fertile offspring called beefalo or zubron.

Description

Magdalenian bison on plaque, 17,000–9,000 BC, Bédeilhac grottoe, Ariège

 

The American bison and the European bison (wisent) are the largest surviving terrestrial animals in North America and Europe. They are typical artiodactyl (cloven hooved) ungulates, and are similar in appearance to other bovines such as cattle and true buffalo. They are broad and muscular with shaggy coats of long hair. Adults grow up to 1.8 metres (5 ft 11 in) in length for American Bison and up to 2.8 metres (9 ft 2 in) in length for European bison. American bison can weigh from approximately 400 kilograms (880 lb) to 900 kg (2,000 lb) and European bison can weight from 800 kilograms (1,800 lb) to 1,000 kilograms (2,200 lb). European bison tend to be taller and heavier than American bison. 

Bison are nomadic grazers and travel in herds. The bulls leave the herds of females at two or three years of age, and join a male herd, which are generally smaller than female herds. Mature bulls rarely travel alone. Towards the end of the summer, for the reproductive season, the sexes necessarily commingle.

American bison are known for living in the Great Plains, but formerly had a much larger range including much of the eastern United States and parts of Mexico. Both species were hunted close to extinction during the 19th and 20th centuries, but have since rebounded; the wisent owing its survival, in part, to the Chernobyl Disaster, ironically, as the Chernobyl Exclusion Zone has become a kind of wildlife preserve for wisent and other rare megafauna such as the Przewalski's Horse, though poaching has become a threat in recent years. The American Plains bison is no longer listed as endangered, but this does not mean the species is secure. Genetically pure B. b. bison currently number only ~20,000, separated into fragmented herds—all of which require active conservation measures. The Wood bison is on the endangered species list in Canada and is listed as threatened in the United States, though there have been numerous attempts by beefalo ranchers to have it entirely removed from the Endangered Species List.

A museum display shows the full skeleton of an adult male American Bison

 

Although superficially similar, physical and behavioural differences exist between the American and European bison. The American species has 15 ribs, while the European bison has 14. The American bison has four lumbar vertebrae, while the European has five. (The difference in this case is that what would be the first lumbar vertebra has ribs attached to it in American bison and is thus counted as the 15th thoracic vertebra, compared to 14 thoracic vertebrae in wisent.) Adult American bison are less slim in build and have shorter legs. American bison tend to graze more, and browse less than their European relatives. Their anatomies reflect this behavioural difference; the American bison's head hangs lower than the European's. The body of the American bison is typically hairier, though its tail has less hair than that of the European bison. The horns of the European bison point through the plane of their faces, making them more adept at fighting through the interlocking of horns in the same manner as domestic cattle, unlike the American bison, which favours butting. American bison are more easily tamed than their European cousins, and breed with domestic cattle more readily.

Evolution and genetic history

The bovine tribe (Bovini) split about 5 to 10 million years ago into the buffalos (Bubalus and Syncerus) and a group leading to bison and taurine cattle. Thereafter, the family lineage of bison and taurine cattle does not appear to be a straightforward "tree" structure as is often depicted in much evolution, because evidence of interbreeding and crossbreeding is seen between different species and members within this family, even many millions of years after their ancestors separated into different species. This crossbreeding was not sufficient to conflate the different species back together, but it has resulted in unexpected relationships between many members of this group, such as yak being related to American bison, when such relationships would otherwise not be apparent. 

A 2003 study of mitochondrial DNA indicated four distinct maternal lineages in tribe Bovini:

1. Taurine cattle and zebu
2. Wisent
3. American bison and yak and
4. Banteng, gaur, and gayal

However, Y chromosome analysis associated wisent and American bison. An earlier study using amplified fragment length polymorphism fingerprinting showed a close association of wisent with American bison, and probably with the yak, but noted that the interbreeding of Bovini species made determining relationships problematic.

The genus Bison diverged from the lineage that led to cattle (Bos primigenius) at the Plio-Pleistocene boundary in South Asia. Two extant and six extinct species are recognised. Of the six extinct species, five went extinct in the Quaternary extinction event. Three were North American endemics: Bison antiquus, B. latifrons, and B. occidentalis. The fourth, B. priscus (steppe bison), ranged across steppe environments from Western Europe, through Central Asia, East Asia including Japan, and onto North America. The fifth, B. schoetensacki (woodland bison), inhabited Eurasian forests, extending from western Europe to the south of Siberia.

Bisons depicted at Cave of Altamira

 

The sixth, B. palaeosinensis, evolving in the Early Pleistocene in South Asia, is presumed to have been the evolutionary ancestor of B. priscus and all successive Bison lineages. The steppe bison (B. priscus) evolved from Bison palaeosinensis in the Early Pleistocene. B. priscus is seen clearly in the fossil record around 2 million years ago. The steppe bison spread across Eurasia, and all proceeding contemporary and successive species are believed to have derived from the steppe bison. Going extinct in 6,000 BCE, outlasted only by B. occidentalis, B. bonasus and B. bison, the steppe bison was the predominant bison pictured in the ancient cave paintings of Spain and Southern France.

The modern European bison is likely to have arisen from the steppe bison. There is no direct fossil evidence of successive species between the steppe bison and the European bison, though there are three possible lines of ancestry pertaining to the European wisent. Past research has suggested that the European bison is descended from bison that had migrated from Asia to North America, and then back to Europe, where they crossbred with existing steppe bison. However, more recent phylogenetic research points to an origin either from the phenotypically and genetically similar Pleistocene woodland bison (B. schoetensacki) or as the result of an interbreeding event between the steppe bison and the aurochs (Bos primigenius), the ancestor of domesticated cattle, around 120,000 years ago. The possible hybrid is referred to in vernacular as the 'Higgs bison' as a hat-tip to the discovery process of the Higgs boson.

At one point, some steppe bison crossbred with the ancestors of the modern yak. After that crossbreeding, a population of steppe bison crossed the Bering Land Bridge to North America. The steppe bison spread through the northern parts of North America and lived in Eurasia until around 11,000 years ago and North America until 4,000 to 8,000 years ago.

The Pleistocene woodland bison (B.schoetensacki) evolved in the Middle Pleistocene from B. priscus, and tended to inhabit the dry conifer forests and woodland which lined the mammoth steppe, occupying a range from western Europe to the south of Siberia. Although their fossil records are far rarer than their antecedent, they are thought to have existed until at least 36,000 BCE.

Bison latifrons (the "giant" or "longhorn" bison) is thought to have evolved in midcontinent North America from B. priscus, after the steppe bison crossed into North America. Giant bison (B. latifrons) appeared in the fossil record about 120,000 years ago. B. latifrons was one of many species of North American megafauna that became extinct during the transition from the Pleistocene to the Holocene epoch (an event referred to as the Quaternary extinction event). It is thought to have disappeared some 21,000–30,000 years ago, during the late Wisconsin glaciation.

B. latifrons co-existed with the slightly smaller B. antiquus for over 100,000 years. Their predecessor, the steppe bison appeared in the North American fossil record around 190,000 years ago. B. latifrons is believed to have been a more woodland-dwelling, non-herding species, while B. antiquus was a herding grassland-dweller, very much like its descendant B. bison. B. antiquus gave rise to both B. occidentalis, and later B. bison, the modern American bison, some 5,000 to 10,000 years ago. B. antiquus was the most common megafaunal species on the North American continent during much of the Late Pleistocene and is the most commonly found large animal found at the La Brea Tar Pits.

In 2016, DNA extracted from Bison priscus fossil remains beneath a 130,000-year-old volcanic ashfall in the Yukon suggested recent arrival of the species. That genetic material indicated that all American bison had a common ancestor 135,000 to 195,000 years ago, during which period the Bering Land Bridge was exposed; this hypothesis precludes an earlier arrival. The researchers sequenced mitochondrial genomes from both that specimen and from the remains of a recently discovered, estimated 120,000-year-old giant, long-horned, B. latifrons from Snowmass, Colorado. The genetic information also indicated that a second, Pleistocene migration of bison over the land bridge occurred 21,000 to 45,000 years ago.

Skulls of European bison (left) and American bison (right)

 

During the population bottleneck, after the great slaughter of American bison during the 19th century, the number of bison remaining alive in North America declined to as low as 541. During that period, a handful of ranchers gathered remnants of the existing herds to save the species from extinction. These ranchers bred some of the bison with cattle in an effort to produce "cattleo" (today called "beefalo") Accidental crossings were also known to occur. Generally, male domestic bulls were crossed with buffalo cows, producing offspring of which only the females were fertile. The crossbred animals did not demonstrate any form of hybrid vigor, so the practice was abandoned. Wisent-American bison hybrids were briefly experimented with in Germany (and found to be fully fertile) and a herd of such animals is maintained in Russia. A herd of cattle-wisent crossbreeds (zubron) is maintained in Poland. First-generation crosses do not occur naturally, requiring caesarean delivery. First-generation males are infertile. The U.S. National Bison Association has adopted a code of ethics that prohibits its members from deliberately crossbreeding bison with any other species. In the United States, many ranchers are now using DNA testing to cull the residual cattle genetics from their bison herds. The proportion of cattle DNA that has been measured in introgressed individuals and bison herds today is typically quite low, ranging from 0.56 to 1.8%.

There are also remnant purebred American bison herds on public lands in North America. Herds of importance are found in Yellowstone National Park, Wind Cave National Park in South Dakota, Blue Mounds State Park in Minnesota, Elk Island National Park in Alberta, and Grasslands National Park in Saskatchewan. In 2015 a purebred herd of 350 individuals was identified on public lands in the Henry Mountains of southern Utah via genetic testing of mitochondrial and nuclear DNA. This study, published in 2015, also showed the Henry Mountains bison herd to be free of brucellosis, a bacterial disease that was imported with non-native domestic cattle to North America.

Behavior

A group of images by Eadweard Muybridge, set to motion to illustrate the movement of the bison

 

A bison charges an elk in Yellowstone National Park.

 

Wallowing is a common behavior of bison. A bison wallow is a shallow depression in the soil, either wet or dry. Bison roll in these depressions, covering themselves with mud or dust. Possible explanations suggested for wallowing behavior include grooming behavior associated with moulting, male-male interaction (typically rutting behavior), social behavior for group cohesion, play behavior, relief from skin irritation due to biting insects, reduction of ectoparasite load (ticks and lice), and thermoregulation. In the process of wallowing, bison may become infected by the fatal disease anthrax, which may occur naturally in the soil.

Bison temperament is often unpredictable. They usually appear peaceful, unconcerned, even lazy, yet they may attack anything, often without warning or apparent reason. They can move at speeds up to 35 mph (56 km/h) and cover long distances at a lumbering gallop.

Their most obvious weapons are the horns borne by both males and females, but their massive heads can be used as battering rams, effectively using the momentum produced by what is a typical weight of 2,000 pounds (900 kg) (can be up to 2700 lbs) moving at 30 mph (50 km/h). The hind legs can also be used to kill or maim with devastating effect. In the words of early naturalists, they were dangerous, savage animals that feared no other animal and in prime condition could best any foe (except for wolves and brown bears).

The rutting, or mating, season lasts from June through September, with peak activity in July and August. At this time, the older bulls rejoin the herd, and fights often take place between bulls. The herd exhibits much restlessness during breeding season. The animals are belligerent, unpredictable, and most dangerous.

Habitat

"Last of the Canadian Buffaloes", 1902, photograph: Steele and Company

 

American bison live in river valleys, and on prairies and plains. Typical habitat is open or semiopen grasslands, as well as sagebrush, semiarid lands, and scrublands. Some lightly wooded areas are also known historically to have supported bison. They also graze in hilly or mountainous areas where the slopes are not steep. Though not particularly known as high-altitude animals, bison in the Yellowstone Park bison herd are frequently found at elevations above 8,000 feet and the Henry Mountains bison herd is found on the plains around the Henry Mountains, Utah, as well as in mountain valleys of the Henry Mountains to an altitude of 10,000 feet. 

European bison tend to live in lightly wooded to fully wooded areas and areas with increased shrubs and bushes, though they can also live on grasslands and plains.

Restrictions

Throughout most of their historical range, landowners have sought restrictions on free-ranging bison. Herds on private land are required to be fenced in. In the state of Montana, free-ranging bison on public lands may be shot, due to concerns about transmission of disease to cattle and damage to public property. In 2013, Montana legislative measures concerning the bison were proposed and passed the legislature, but opposed by Native American tribes as they impinged on sovereign tribal rights. Three such bills were vetoed by Steve Bullock, the governor of Montana. The bison's circumstances remain an issue of contention between Native American tribes and private landowners.

Diet

A bison and an elk grazing together in the Yellowstone National Park.

 

Bison are ruminants, which allows them to derive their energy from cell walls. Bison were once thought to almost exclusively consume grasses and sedges, but are now known to consume a wide-variety of plants including woody plants and herbaceous eudicots. Over the course of the year, bison shift which plants they select in their diet based on which plants have the highest protein or energy concentrations at a given time and will reliably consume the same species of plants across years. Protein concentrations of the plants they eat tend to be highest in the spring and decline thereafter, reaching their lowest in the winter. In Yellowstone National Park, bison browsed willows and cottonwoods, not only in the winter when few other plants are available, but also in the summer. Bison are thought to migrate to optimize their diet, and will concentrate their feeding on recently burned areas due to the higher quality forage the regrows after the burn. Wisent tend to browse on shrubs and low-hanging trees more often than do the American bison, which prefer grass to shrubbery and trees.

Reproduction

Female bison typically do not reproduce until three years of age and can reproduce to at least 19 years of age. Female bison can produce calves annually as long as their nutrition is sufficient, but will not give birth to a calf after years where weight gain was too low. A mother's probability of reproduction the following year is strongly dependent on the mother's mass and age. Heavier female bison produce heavier calves (weighed in the fall at weaning) than light mothers, while the weight of calves is lower for older mothers (after age 8).

Predators

Wolves hunting bison

Due to their size, bison have few predators. Five notable exceptions are humans, the wolf, mountain lion, brown bear, and coyote. The grey wolf generally takes down a bison while in a pack, but cases of a single wolf killing bison have been reported. Brown bear also consume bison, often by driving off the pack and consuming the wolves' kill. Brown bear and coyotes also prey on bison calves. Historically and prehistorically, lions, tigers, Smilodon, Homotherium, cave hyenas and Homo sp. had posed threats to bison.

Infections and illness

For the American bison, the main cause of illness is malignant catarrhal fever, though brucellosis is a serious concern in the Yellowstone Park bison herd. Bison in the Antelope Island bison herd are regularly inoculated against brucellosis, parasites, Clostridium infection, infectious bovine rhinotracheitis, and bovine vibriosis.

The major concerns for illness in European bison are foot-and-mouth disease and balanoposthitis, which affects the male sex organs; a number of parasitic diseases have also been cited as threats. The inbreeding of the species caused by the small population plays a role in a number of genetic defects and immunity to diseases, which in turn poses greater risks to the population.

Name

The term "buffalo" is sometimes considered to be a misnomer for this animal, as it is only distantly related to either of the two "true buffalo", the Asian water buffalo and the African buffalo. Samuel de Champlain applied the term buffalo (buffles in French) to the bison in 1616 (published 1619), after seeing skins and a drawing shown to him by members of the Nipissing First Nation, who said they travelled forty days (from east of Lake Huron) to trade with another nation who hunted the animals. Though "bison" might be considered more scientifically correct, as a result of standard usage, "buffalo" is also considered correct and is listed in many dictionaries as an acceptable name for American buffalo or bison. Buffalo has a much longer history than bison, which was first recorded in 1774.

Human impact

Photo from the 1870s of a pile of American bison skulls waiting to be ground for fertilizer.

 

Humans were almost exclusively accountable for the near-extinction of the American bison in the 1800s. At the beginning of the century, tens of millions of bison roamed North America. American settlers slaughtered an estimated 50 million bison during the 19th century. Railroads were advertising "hunting by rail", where trains encountered large herds alongside or crossing the tracks. Men aboard fired from the trains roof or windows, leaving countless animals to rot where they died. The overhunting of the bison reduced their population to hundreds. Attempts to revive the American bison have been highly successful; farming has increased their population to nearly 150,000. The American bison is, therefore, no longer considered an endangered species.

As of July 2015, an estimated 4,900 bison lived in Yellowstone National Park, the largest U.S. bison population on public land. During 1983–1985 visitors experienced 33 bison-related injuries (range = 10–13/year), so the park implemented education campaigns. After years of success, five injuries associated with bison encounters occurred in 2015, because visitors did not maintain the required distance of 75 ft (23 m) from bison while hiking or taking pictures.

Nutrition

Bison is an excellent source of complete protein and a rich source (20% or more of the Daily Value, DV) of multiple vitamins including Riboflavin, Niacin, Vitamin B6, and Vitamin B12 and is also a rich source of minerals including iron, phosphorus, and zinc. Additionally, bison is a good source (10% or more of the Daily Value) of thiamine.

Bison, ground, grass-fed, cooked

Nutritional value per 100 g (3.5 oz)
Energy	179 kcal (750 kJ)
Carbohydrates	0.00 g
Sugars	0 g
Dietary fiber	0 g
Fat	8.62 g
Saturated	3.489 g
Monounsaturated	3.293g
Polyunsaturated	0.402 g
Protein	25.45 g
Vitamins	Quantity %DV†
Thiamine (B1)	12% 0.139 mg
Riboflavin (B2)	22% 0.264 mg
Niacin (B3)	40% 5.966 mg
Vitamin B6	31% 0.401 mg
Folate (B9)	4% 16 μg
Vitamin B12	102% 2.44 μg
Vitamin D	0% 0 IU
Vitamin E	1% 0.20 mg
Vitamin K	1% 1.3 μg
Minerals	Quantity %DV†
Calcium	1% 14 mg
Iron	25% 3.19 mg
Magnesium	6% 23 mg
Phosphorus	30% 213 mg
Potassium	8% 353 mg
Sodium	5% 76 mg
Zinc	56% 5.34 mg
link to USDA Database entry
Units μg = micrograms • mg = milligrams IU = International units
†Percentages are roughly approximated using US recommendations for adults. Source: USDA Nutrient Database

Livestock

Early instances of pre-Columbian domestication of bison include reports by an early Spanish source of domestication by Amerindians (including the "milking" of bison), and Montezuma's zoo at Tenochtitlan, the Aztec capital, which included bison, which the Spaniards called "the Mexican bull."Bison are increasingly raised for meat, hide, wool, and dairy products. The majority of bison in the world are raised for human consumption or fur clothing. Bison meat is generally considered to taste very similar to beef, but is lower in fat and cholesterol, yet higher in protein than beef, which has led to the development of beefalo, a fertile hybrid of bison and domestic cattle. A market even exists for kosher bison meat; these bison are slaughtered at one of the few kosher mammal slaughterhouses in the U.S. and Canada, and the meat is then distributed worldwide.

In America, the commercial industry for bison has been slow to develop despite individuals, such as Ted Turner, who have long marketed bison meat. In the 1990s, Turner found limited success with restaurants for high-quality cuts of meat, which include bison steaks and tenderloin. Lower-quality cuts suitable for hamburger and hot dogs have been described as "almost nonexistent". This created a marketing problem for commercial farming because the majority of usable meat, about 400 pounds for each bison, is suitable for these products. In 2003, the United States Department of Agriculture purchased $10 million worth of frozen overstock to save the industry, which would later recover through better use of consumer marketing. Restaurants have played a role in popularizing bison meat, like Ted's Montana Grill, which added bison to their menus. Ruby Tuesday first offered bison on their menus in 2005.

In Canada, commercial bison farming began in the mid 1980s, concerning an unknown number of animals then. The first census of the bison occurred in 1996, which recorded 45,235 bison on 745 farms, and grew to 195,728 bison on 1,898 farms for the 2006 census.

Several pet food companies use bison as a red meat alternative in dog foods. The companies producing these formulas include Natural Balance Pet Foods, Freshpet, The Blue Buffalo Company, Solid Gold, Canidae, and Taste of the Wild.