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Ruminants (
suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: life, domain (biology), do ...
Ruminantia) are large hoofed herbivorous grazing or browsing
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s that are able to acquire nutrients from plant-based food by
fermenting Fermentation is a metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signalin ...
it in a specialized
stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated structure and functions as a vital organ. In the digestive system the stomach is involved in the second phase of digestion, ...

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 fermentationForegut fermentation is a form of digestion that occurs in the foregut The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the ...
, typically requires the fermented ingesta (known as
cud Cud is a portion of food that returns from a ruminant Ruminants are herbivorous mammals of the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to ...
) 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 ruminants include both domestic and wild species. Ruminating mammals include
cattle Cattle, taurine cattle, Eurasian cattle, or European cattle (''Bos taurus'' or ''Bos primigenius taurus'') are large domestication, domesticated Cloven hoof, cloven-hooved herbivores. They are a prominent modern member of the subfamily Bovinae ...

cattle
, all domesticated and wild
bovine The biological subfamily In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characte ...

bovine
s,
goat The domestic goat or simply goat (''Capra hircus'') is a domesticated species of typically kept as . It was from the (''C. aegagrus'') of and . The goat is a member of the animal family and the subfamily , meaning it is closely related ...

goat
s,
sheep Sheep (''Ovis aries'') are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order (biology), order Artiodactyla, the even-toed ungulates. Although the name ''sheep'' applies to many species ...

sheep
,
giraffe The giraffe is a tall African mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Fe ...

giraffe
s,
deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , and the ; and the , including the (caribou), , the , and the . Male deer of all species (except the Chinese ) as we ...

deer
,
gazelle A gazelle is any of many antelope species in the genus ''Gazella''. This article also deals with the seven species included in two further genera, ''Eudorcas'' and ''Nanger'', which were formerly considered subgenera of ''Gazella''. A third for ...

gazelle
s, and
antelope The term antelope is used to refer to many species of even-toed ruminant Ruminants (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by ...

antelope
s.Fowler, M.E. (2010).
Medicine and Surgery of Camelids
, Ames, Iowa: Wiley-Blackwell. Chapter 1 General Biology and Evolution addresses the fact that camelids (including camels and llamas) are not ruminants, pseudo-ruminants, or modified ruminants.
It has also been suggested that notoungulates also relied on rumination, as opposed to other atlantogenates that rely on the more typical
hindgut fermentationHindgut fermentation is a digestive process seen in monogastric herbivore 250px, Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse">alga.html" ;"title="radulas, scraping green alg ...
, though this is not entirely certain. Taxonomically, the suborder
Ruminantia Ruminantia is a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ...

Ruminantia
is a lineage of herbivorous
artiodactyls
artiodactyls
that includes the most advanced and widespread of the world's
ungulate Ungulates ( ) are members of the diverse clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evoluti ...
s. The suborder Ruminantia includes six different families: Tragulidae,
Giraffidae The Giraffidae are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of societ ...
,
Antilocapridae The Antilocapridae are a family of artiodactyls endemic to North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subco ...
,
Moschidae Moschidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well ...
,
Cervidae Deer or true deer are hoof A hoof ( or ), plural hooves ( or ) or hoofs , is the tip of a toe Toes are the digits (fingers) of the foot of a tetrapod. Animal Animals (also called Metazoa) are multicellular eukaryotic organis ...

Cervidae
, and
Bovidae The Bovidae comprise the biological family Family ( la, familia, plural ') is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy; it is classified between order (biology), order and genus. A family may be divided into su ...
.


Taxonomy and evolution

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
pseudoruminantPseudoruminant is a classification of animals based on their digestive tract differing from the ruminant Ruminants are herbivorous mammals of the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, ...
s, which have a three-compartment stomach instead of four like ruminants. The
Hippopotamidae :''This is the article on the family Hippopotamidae; for the main article on hippos, see Hippopotamus The hippopotamus ( ; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus or river hippopotamus, is a large, mostly herbi ...

Hippopotamidae
(comprising
hippopotami The hippopotamus ( ; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus or river hippopotamus, is a large, mostly herbivore, herbivorous, List of semiaquatic tetrapods, semiaquatic mammal and ungulate native to sub-Saharan ...

hippopotami
) are well-known examples. Pseudoruminants, like traditional ruminants, are foregut fermentors and most ruminate or chew
cud Cud is a portion of food that returns from a ruminant Ruminants are herbivorous mammals of the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to ...
. However, their anatomy and method of digestion differs significantly from that of a four-chambered ruminant. Monogastric
herbivore A herbivore is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of ...
s, such as
rhinoceros A rhinoceros (, , ), commonly abbreviated to rhino, is a member of any of the five extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. T ...

rhinoceros
es,
horse The horse (''Equus ferus caballus'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to ...

horse
s, and
rabbits Rabbits are small mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammali ...

rabbits
, are not ruminants, as they have a simple single-chambered stomach. These hindgut fermenters digest cellulose in an enlarged
cecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (o ...

cecum
. In smaller hindgut fermenters of the
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
Lagomorpha The lagomorphs are the members of the taxonomic order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from g ...

Lagomorpha
(rabbits, hares, and
pika A pika ( ; archaically spelled pica) is a small, mountain-dwelling mammal found in Asia and North America. With short limbs, very round body, an even coat of fur, and no external tail, they resemble their close relative, the rabbit, but with sho ...

pika
s), cecotropes formed in the cecum are passed through the large intestine and subsequently reingested to allow another opportunity to absorb nutrients.


Phylogeny

Ruminantia is a
crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
of ruminants within the
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
Artiodactyla The even-toed ungulates (Artiodactyla , ) are ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , ...

Artiodactyla
,
cladistically Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistically
defined by Spaulding et al. as "the least inclusive clade that includes ''
Bos taurus Cattle, taurine cattle, Eurasian cattle, or European cattle (''Bos taurus'' or ''Bos primigenius taurus'') are large domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a signific ...
'' (cow) and ''
Tragulus napu The greater mouse-deer, greater Malay chevrotain, or napu (''Tragulus napu'') is a species of even-toed ungulate in the family Tragulidae found in Sumatra, Borneo, and smaller Malaysian and Indonesian islands, and in southern Myanmar, southern Th ...

Tragulus napu
'' (mouse deer)". Ruminantiamorpha is a higher-level
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
of artiodactyls,
cladistically Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistically
defined by Spaulding et al. as "Ruminantia plus all extinct taxa more closely related to extant members of Ruminantia than to any other living species." This is a stem-based definition for Ruminantiamorpha, and is more inclusive than the
crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
Ruminantia. As a crown group, Ruminantia only includes the
last common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
of all
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
(living) ruminants and their descendants (living or
extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
), whereas Ruminantiamorpha, as a stem group, also includes more
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
extinct ruminant ancestors that are more closely related to living ruminants than to other members of Artiodactyla. When considering only living taxons (
neontology Neontology is a part of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ph ...
), this makes Ruminantiamorpha and Ruminantia
synonymous A synonym is a word, morpheme A morpheme is the smallest meaningful lexical item in a language. A morpheme is not a word. The difference between a morpheme and a word is that a morpheme bound and free morphemes, sometimes does not stand alone, ...
, and only Ruminantia is used. Thus, Ruminantiamorpha is only used in the context of
paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes th ...
. Accordingly, Spaulding grouped some genera of the
extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
family
Anthracotheriidae Anthracotheriidae is a paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroup ...
within Ruminantiamorpha (but not in Ruminantia), but placed others within Ruminantiamorpha's sister clade,
Cetancodontamorpha Cetancodontamorpha is a total clade of artiodactyls defined, according to Spaulding ''et al''., as Whippomorpha "plus all extinct taxa more closely related to extant members of Whippomorpha than to any other living species". Attempts have been ma ...
. Ruminantia's placement within
Artiodactyla The even-toed ungulates (Artiodactyla , ) are ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , ...

Artiodactyla
can be represented in the following
cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

cladogram
:(see e.g. Fig S10) Within Ruminantia, the Tragulidae (mouse deer) are considered the most
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
family, with the remaining ruminants classified as belonging to the
infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, ...
Pecora Pecora is an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...

Pecora
. Until the beginning of the 21st century it was understood that the family
Moschidae Moschidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well ...
(musk deer) was
sister A sister is a woman A woman is an adult female Female (symbol: ♀) is the sex of an organism, or a part of an organism, that produces non-mobile ovum, ova (egg cells). Barring rare medical conditions, most female mammals, including fema ...
to
Cervidae Deer or true deer are hoofed ruminant mammals forming the family (biology), family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, includ ...

Cervidae
. However, a 2003
phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

phylogenetic
study by Alexandre Hassanin (of
National Museum of Natural History, France The French National Museum of Natural History, known in French as the (MNHN; ), is the natural history museum Skeletons of '' Finnish_Museum_of_Natural_History_in_Helsinki.html" ;"title="Giganotosaurus">Shunosaurus'' (left) and ''Giganotosaur ...
) and colleagues, based on
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
l and nuclear analyses, revealed that
Moschidae Moschidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well ...
and
Bovidae The Bovidae comprise the biological family Family ( la, familia, plural ') is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy; it is classified between order (biology), order and genus. A family may be divided into su ...
form a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
sister to
Cervidae Deer or true deer are hoofed ruminant mammals forming the family (biology), family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, includ ...

Cervidae
. According to the study, Cervidae diverged from the Bovidae-Moschidae clade 27 to 28 million years ago. The following
cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

cladogram
is based on the 2003 study.


Classification

* ORDER
ARTIODACTYLA The even-toed ungulates (Artiodactyla , ) are ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , ...

ARTIODACTYLA
** Suborder
Tylopoda Tylopoda (meaning "calloused foot") is a suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks ...
:
camel A camel is an even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, ...

camel
s and
llama The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a List of meat animals, meat and pack animal by Inca empire, Andean cultures since the Pre-Columbian era. Llamas are social animals and live with othe ...

llama
s, 7 living species in 3 genera ** Suborder
Suina Suina (also known as Suiformes) is a suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in d ...
:
pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and ani ...

pig
s and
peccaries A peccary (also javelina or skunk pig) is a medium-sized pig-like Ungulate, hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central America, Central and South America, Trinidad in the Caribbean, and in the sout ...
** Suborder
Cetruminantia The Cetruminantia are a clade made up of the Cetancodontamorpha (or Whippomorpha) and their closest living relatives, the Ruminantia. Cetruminantia's placement within Artiodactyla can be represented in the following cladogram:(see e.g. Fig S10) ...
: ruminants,
whale Whales are a widely distributed and diverse group of fully aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is ...

whale
s and
hippo The hippopotamus ( ; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus or river hippopotamus, is a large, mostly herbivorous File:Land_Snail_radula_tracks.jpg#, 250px, Tracks made by terrestrial gastropods with their ...

hippo
s *** unranked Ruminantia **** Infraorder
Tragulina Tragulina is an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
(paraphyletic) ***** Family † Prodremotheriidae ***** Family †
Hypertragulidae Hypertragulidae is an extinct family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to m ...
***** Family † Praetragulidae ***** Family † Protoceratidae ***** Family Tragulidae:
chevrotain Chevrotains, or mouse-deer, are small even-toed ungulates that make up the family (biology), family Tragulidae, the only extant members of the infraorder Tragulina. The 10 Extant taxon, extant species are placed in three genera, but several ...
s, 6 living species in 4 genera ***** Family † Archaeomerycidae ***** Family † Lophiomerycidae **** Infraorder
Pecora Pecora is an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...

Pecora
***** Family
Cervidae Deer or true deer are hoofed ruminant mammals forming the family (biology), family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, includ ...

Cervidae
:
deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , and the ; and the , including the (caribou), , the , and the . Male deer of all species (except the Chinese ) as we ...

deer
and
moose The moose (in North America) or elk (in Eurasia) (''Alces alces'') is a member of the New World deer subfamily and is the largest and heaviest extant Extant is the opposite of the word extinct Extinction is the termination of a kind of ...

moose
, 49 living species in 16 genera ***** Family †
Gelocidae The Gelocidae are an extinct group of hornless ruminantia Ruminantia is a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proce ...
***** Family †
Palaeomerycidae The Palaeomerycidae are an extinct family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is ...
***** Family † Hoplitomerycidae ***** Family †
Climacoceratidae Climacoceratidae is a family of superficially deer-like artiodactyl ungulates which lived in the Miocene epoch in Africa. They are close to the ancestry of Giraffidae, giraffes, with some genera, such as ''Prolibytherium'', originally classified a ...
***** Family
Giraffidae The Giraffidae are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of societ ...
:
giraffe The giraffe is a tall African mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Fe ...

giraffe
and
okapi The okapi (; ''Okapia johnstoni''), also known as the forest giraffe, Congolese giraffe, or zebra giraffe, is an artiodactyl mammal that is endemic to the northeast Democratic Republic of the Congo in central Africa. Although the okapi has st ...

okapi
, 2 living species in 2 genera ***** Family
Antilocapridae The Antilocapridae are a family of artiodactyls endemic to North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subco ...
:
pronghorn The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulate Ungulates ( ) are members of the diverse clade A clade (; from grc, , ''klados'', "branch"), also known ...

pronghorn
, one living species in one genus ***** Family † Leptomerycidae ***** Family
Moschidae Moschidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well ...
:
musk deer Musk deer can refer to any one, or all seven, of the species that make up ''Moschus'', the only extant genus of the family (biology), family Moschidae. Despite being commonly called deer, they are not true deer belonging to the family Cervidae bu ...
, 4 living species in one genus ***** Family
Bovidae The Bovidae comprise the biological family Family ( la, familia, plural ') is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy; it is classified between order (biology), order and genus. A family may be divided into su ...
:
cattle Cattle, taurine cattle, Eurasian cattle, or European cattle (''Bos taurus'' or ''Bos primigenius taurus'') are large domestication, domesticated Cloven hoof, cloven-hooved herbivores. They are a prominent modern member of the subfamily Bovinae ...

cattle
,
goat The domestic goat or simply goat (''Capra hircus'') is a domesticated species of typically kept as . It was from the (''C. aegagrus'') of and . The goat is a member of the animal family and the subfamily , meaning it is closely related ...
s,
sheep Sheep (''Ovis aries'') are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order (biology), order Artiodactyla, the even-toed ungulates. Although the name ''sheep'' applies to many species ...

sheep
, and
antelope The term antelope is used to refer to many species of even-toed ruminant Ruminants (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by ...

antelope
, 143 living species in 53 genera


Digestive system of ruminants

The primary difference between ruminants and nonruminants is that ruminants' stomachs have four compartments: #
rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allows ...
—primary site of microbial fermentation #
reticulum Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net (device), net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions. The constellation is be ...
#
omasum The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated st ...
—receives chewed cud, and absorbs volatile fatty acids #
abomasum The ruminant digestive system The abomasum, also known as the maw,
—true stomach The first two chambers are the rumen and the reticulum. These two compartments make up the fermentation vat and 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 Saliva (commonly referred to as spit) is an extracellular fluid In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including t ...
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 Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
and
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...

hemicellulose
, is primarily broken down in these chambers by microbes (mostly
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
, as well as some
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of single-celled eukaryote Eukaryotes () are organism In biology, an organism () is any organic, life, living system that ...

protozoa
,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
, and
yeast Yeasts are eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

yeast
) into the three
volatile fatty acids Short-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestine, intestinal microbe, microbial fermentation of indigestible foods, SCFAs are the main energy source of Gastrointestinal_tract#Mucosa, colonocyte ...
(VFAs):
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
,
propionic acid Propionic acid (, from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population ...

propionic acid
, and
butyric acid Butyric acid (from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study o ...

butyric acid
. Protein and nonstructural carbohydrate (
pectin Pectin (from grc, πηκτικός ', "congealed, curdled") is a structural acidic heteropolysaccharide contained in the primary and middle lamella The middle lamella is a layer that cements together the primary cell wall A cell wall is a ...

pectin
,
sugars Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides o ...
, 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
monogastricA monogastric organism has a simple single-chambered stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and func ...
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 The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

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 The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human dig ...

large intestine
in the same way as in the reticulorumen. Only small amounts of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

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 Lactose, a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose ...

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 Glycogen is a multibranched polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () usi ...

glycogen
produced and protein for another 20% (50% under starvation conditions).


Abundance, distribution, and domestication

Wild ruminants number at least 75 millionHackmann. T. J., and Spain, J. N. 201
"Ruminant ecology and evolution: Perspectives useful to livestock research and production"
''Journal of Dairy Science'', 93:1320–1334
and are native to all continents except Antarctica and Australia. 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 Forage is a plant material (mainly plant leaves and stems) eaten by grazing In agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentism, se ...

forage
causes abrasion of the teeth. This 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

Vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s lack the ability to hydrolyse the beta –4glycosidic bond of plant cellulose due to the lack of the enzyme
cellulase Cellulase is any of several enzymes Enzymes () are protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of ...
. Thus, ruminants 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 Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
,
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of single-celled eukaryote Eukaryotes () are organism In biology, an organism () is any organic, life, living system that ...

protozoa
, sometimes
yeasts Yeasts are eukaryotic Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It ...
and other
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

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 Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...
, most of these microbial species are
obligate{{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe 300px, Aerobic and anaerobic bacteria can be identified by growing them in test tub ...
or
facultative {{wiktionary, facultative Facultative means "optional" or "discretionary" (antonym '' obligate''), used mainly in biology in phrases such as: * Facultative (FAC), facultative wetland (FACW), or facultative upland (FACU): wetland indicator statuses ...
anaerobes that can decompose complex plant material, such as
cellulose Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
,
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...

hemicellulose
,
starch Starch or amylum is a polymeric A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance ...
, and
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...
s. The hydrolysis of cellulose results in sugars, which are further fermented to acetate, lactate, propionate, butyrate, carbon dioxide, and
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
. 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 ruminant digestive system The abomasum, also known as the maw,
. The enzyme
lysozyme Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, is an antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an ...

lysozyme
has adapted to facilitate digestion of bacteria in the ruminant abomasum.
Pancreatic ribonuclease Pancreatic ribonucleases (, ''RNase'', ''RNase I'', ''RNase A'', ''pancreatic RNase'', ''ribonuclease I'', ''endoribonuclease I'', ''ribonucleic phosphatase'', ''alkaline ribonuclease'', ''ribonuclease'', ''gene S glycoproteins'', ''Ceratitis capi ...
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 passes 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

Tannin Tannins (or tannoids) are a class of astringent 200px, A crystal of the astringent alum An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissue In biology Biology is the natural scie ...
s are
phenolic compounds In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen O ...

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 tannin Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are biopolymer, polymers formed by the Condensation reaction, condensation of flavans. They do n ...
s. 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.B.R Min, et al (2003
The effect of condensed tannins on the nutrition and health of ruminants fed fresh temperate forages: a review
Animal Feed Science and Technology 106(1):3–19
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 Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect on ...

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
lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
s and
extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chem ...
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallograp ...
s that have a high affinity to binding to tannins. Some ruminants (goats, deer, elk, moose) are able to consume food high in tannins (leaves, twigs, bark) due to the presence in their saliva of tannin-binding proteins.


Religious importance

The
Law of Moses The Law of Moses ( he, תֹּורַת מֹשֶׁה ), also called the Mosaic Law, primarily refers to the Torah The Torah (; he, תּוֹרָה, "Instruction", "Teaching" or "Law") includes the first five books of the Hebrew Bible ...
in the
Bible The Bible (from Koine Greek Koine Greek (, , Greek approximately ;. , , , lit. "Common Greek"), also known as Alexandrian dialect, common Attic, Hellenistic or Biblical Greek, was the koiné language, common supra-regional form of Gree ...

Bible
allowed the eating of some mammals that had cloven hoof, cloven hooves (i.e. members of the order
Artiodactyla The even-toed ungulates (Artiodactyla , ) are ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , ...

Artiodactyla
) and "that chew the cud", a stipulation preserved to this day in Jewish kashrut, dietary laws.


Other uses

The verb 'to ruminate' has been extended metaphorically to mean to ponder thoughtfully or to meditation, 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 (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 archea, 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.Intergovernmental Panel on Climate Change, IPCC Fifth Assessment Report
Table 8.7, Chap. 8, pp. 8–58
(PDF)
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.Yavitt, J. B. 1992. Methane, biogeochemical cycle. pp. 197–207 in Encyclopedia of Earth System Science, Vol. 3. Acad.Press, London. The current U.S. domestic beef and dairy cattle population is around 90 million head, approximately 50% higher than the peak wild population of American Bison of 60 million head in the 1700s, which primarily roamed the part of North America that now makes up the United States.


See also

* Monogastric * Pseudoruminant


References


External links


Digestive Physiology of Herbivores
– Colorado State University (Last updated on 13 July 2006) *Britannica, The Editors of Encyclopaedia. "Ruminant". Encyclopedia Britannica, Invalid Date, https://www.britannica.com/animal/ruminant. Accessed 22 February 2021. * {{Authority control Herbivorous mammals Even-toed ungulates Extant Ypresian first appearances