Bos taurus, cattle, cow

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Taxonomy

Cattle belong to an ancient and diverse group of mammals, Cetartiodactyla (even-toed ungulates, includes whales, hippos, ruminants, pigs, camels etc.) that first appeared around 60 million years ago. The two principal taxonomic groups of domestic cattle, Bos taurus (taurine cattle) and Bos indicus (zebu cattle) diverged from a common ancestor 250,000 years ago, and have had been associated with human civilization since Neolithic times 8,000–10,000 years ago. All modern cattle breeds originate from large populations of the ancestral aurochs (Bos taurus primigenius).

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Burt DW. The cattle genome reveals its secrets. J Biol. 2009; 8(4): 36. (BioMed Central Open Access license)

Bovinae have diverged into (a) cattle (b) antelope and (c) buffalo over a relatively short time period. (a) shows a domesticated cow (Bos taurus) (photograph by Daniel Schwen, Wikipedia), (b) is the Common Eland (Taurotragus oryx) (Ablestock) and (c) is a Cape Buffalo (Syncerus caffer) (Ablestock).

A phylogeny using unambiguous sites in the Bovinae results in three main groups: cattle, bison (a) and sister group, yak (b) and banteng (c). (a) shows North American Bison (Bison bison), (b) Yak (Bos grunniens) and (c) Banteng (Bos javanicus). All photographs are from Ablestock.

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Taxonomic lineage of Bos taurus

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Sarcopterygii - Tetrapoda - Amniota - Mammalia - Theria - Eutheria - Laurasiatheria - Cetartiodactyla - Ruminantia - Pecora - Bovidae - Bovinae - Bos - Bos taurus

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General description

• Domestic cows are common throughout the world. They are grown and bred for food - meat and milk production, as well as for working - plowing and moving heavy loads.
• Domestic cows are social animals and live in herds which are structured according to a dominance hierarchy.
• Cows feed on grasses and other herbaceous plants. An average cow can consume about 70 kg of grass in an 8 hour day. Cows are ruminants. They have a four chambered stomach.

Cow's milk allergy vs. cow's milk intolerance

• Cow's milk allergy and cow's milk intolerance are two different concepts that are used interchangeably. The former is an immunologically mediated reaction to the milk's contents, not unlike to any other allergic reactions, for example, to eggs, corn, nuts, etc. The latter is non-immunologic reaction to the cow's milk, the most common cause of which is deficiency of lactase - the enzyme that breaks down one of the main nutrients of the milk - lactose.

Importance of bovine genome

• The bovine genome serves as a reference non-primate, non-rodent, eutherian genome.
• During its domestication, the cow has undergone intense selection for three major phenotypes that are relevant to various aspects of human health research: production of meat, production of milk, and physical strength.
• Contribution of bovine research to the basic understanding of human endocrinology and physiology is dificult to overestimate: bovine insulin as a treatment of human diabetes; discovery of parathyroid hormone; studies of growth promoting effects of growth hormone and luteotrophic effect of luteinizing hormone, etc.
• The bovine model provided the fundamental research platform for developing human reproductive techniques and for studying reproductive diseases. Current reproductive techniques used in humans such as superovulation, oocyte culturing, in-vitro fertilization, and embryo maturation, transfer, and freezing, are based upon many years of research with bovine embryos.
• Research comparing different cattle breeds has identified genetic differences in fat disposition of different organs. Such information provides an experimental model for understanding obesity and nutrition.

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Developmental stages (life cycle)

Life Cycle Stages

• prenatal
  • oocyte MeSH
  • embryo average gestation time in cattle is about 285 days; there are, however, documented breed differences; inter-calving periods are a little more than one year MeSH
    • early gestation embryo
      • pre-implantation embryo
        • zygote MeSH fertilized egg,
          1-cell embryo,
          0 days post-conception (d.p.c.)
        • cleavage MeSH dividing egg, 2-16 cell embryo;
          2-5 days p.c.
          • 2-cell embryo 1 d.p.c.
          • 4-cell embryo 2 d.p.c.
          • 8-cell embryo 3 d.p.c.
          • 16-cell embryo 4 d.p.c.
        • morula MeSH 32-64 cell embryo; 4-5 d.p.c.
        • blastocyst MeSH also blastula; 6-9 d.p.c.
          • early blastocyst 6 d.p.c., ~128 cells
          • blastocyst 6-7 d.p.c.; ~250 cells
          • expanded blastocyst 6.5-7.5 d.p.c.
          • hatched blastocyst 7-8 d.p.c.
          • expanding
            hatched blastocyst 8-9 d.p.c.
        • gastrula MeSH cattle embryos implant after
          gastrulation (unlike rodent
          embryos)
          • spherical embryo up to ~14 d.p.c.
          • ovoid embryo 14-16 d.p.c.
          • elongated embryo 16-18 d.p.c.
      • peri-implantation
        embryo implantation begins in ~22
        days p.c. and completes
        in ~40 d.p.c.
    • post implantation embryo
      • mid-gestation embryo 40-180 days p.c.
      • late gestation embryo
        • fetus MeSH
• post natal
  • neonate 0-3 days of age; newborn is able to stand and walk soon after birth; at birth, the abomasum is the dominant structure (accounts for about 70% of the volume of the entire stomach) while the rumen is basically non functional and the calf is non-ruminant
  • calf juvenile; until age of reproductive maturity
    • pre-ruminant calf calf with under-developed rumen (until 2-3 weeks of age); during the first two weeks of life, the calf relies almost entirely on mother's milk and consumes negligible amounts of dry matter
    • transitional calf the calf starts to consume some starter dry feed; this period lasts until the calf is weaned; during this time, the initial fermentation of dry food begins in reticulorumen that leads to production of first batches of volatile fatty acids (VFA); it leads to rapid expansion of volume and differentiation of the rumen epithelium so that VFA can be absorbed and used
    • ruminant calf abomasum accounts for less than 25% of the total volume; calfs are usually moved from transitional pens at approximately 10 to 14 weeks of age; ruminant phase lasts the rest of animal's life; the ruminant depends on fermentation of dietary carbohydrates for most of its energy in the form of VFA
  • adult abomasum accounts for less than 10% of the total volume; sexual maturity is attained at about 1-1.5 years of age and 250-300 kg body weight; standing to be mounted is the useful sign used by dairy herdsmen for determining the female cow receptivity (estrus); copious quantities of clear elastic mucus flow from the vulva that becomes swollen and reddened at estrus; first calving occurs at about 2 years of age; the young cows having calved for the first time are called heifers; maximum lifespan in domestic cows may exceed 20 years

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Digestive system

• stomach MeSH
  • rumen MeSH the first division of the stomach, in which most food collects immediately after being swallowed; it contains microorganisms for cellulose digestion and fermentation; after being pre-processed in the rumen, food returns to the mouth as cud for further chewing
  • reticulum MeSH the second compartment of the stomach, lined with a membrane having honeycombed ridges; cellulose digestion, fermentation and absorption continues here
  • omasum MeSH also called manyplies; it is the third division of the stomach, located between the abomasum and the reticulum; it is filled with numerous leaf-like fronds, which increase the surface area for fluid absorption
  • abomasum MeSH the fourth division of the stomach is the true stomach, containing glands for protein digestion

Some cattle species

• Banteng, also Bali cattle, (Bos javanicus) inhabits various areas in Southeast Asia. They are wild as well as domesticated. Several subspecies exist.
• The gaur (Bos gaurus) is distributed in South Asia and Southeast Asia.
• The yak, also gayal or mithan, (Bos grunniens) has a dark black-brown coat, dense, wooly, and extremely shaggy. Wild and domesticated animals exist. The distribution is believed to be limited to the Tibetan Plateau, but might extend to other regions with same climate.
• The zebu (Bos indicus) is known as 'humped cattle' or 'indicus' cattle. They are a type of cattle better-adapted to tropical environments.
• The wisent, also, zubr, (Bison bonasus) a species of Eurasian bison. It is the heaviest surviving land animal in Europe

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Cattle domestication

• Archaeological and DNA studies have demonstrated that zebu and cow were domesticated separately but occurrences of interbreeding are speculated as possible. Please note that cattle domestication is one of the hottest and most debated topics between geneticists, archeologists, and zoologists.
• Widely accepted theory is that common ancestor of zebu, as well as taurine cattle, was legendary auroch, or urus. It is also mentioned that divergence between zebu and cow occured not long (a few thousand years) ago before the domestication event.
• Initially, origin of European cattle was traced to a single domestication event that occured in Near East in so called Fertile Crescent region. However, some researchers and philosophers tried to put this theory to a test. Consider this quote attributed to Julius Caesar about aurochs: "They are a little below the elephant in size, and of the appearance, color, and shape of a bull. Their strength and speed are extraordinary; they spare neither man nor wild beast which they have espied." Fundamentally, this and many other accounts, imply that wild cattle were powerful independent animals that unlike pigs, cats or dogs, did not seek human company. It is doubtful that they were domesticated spontaneously as a by-product of agricultural achievements of our ancestors. They had to be overpowered purposefully and systematically. One of the interesting theories considers religious reason of the cattle domestication: capture and sacrificial rituals, symbolic castration (ox), etc. Some captured wild animals may had been kept in enclosures for a long time, which allowed for survival (i.e. selection) of more docile and smaller animals that gradually started to be utilized in agriculture.

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Photo gallery

Resting cows

Brahman

Juvenile bison

Mother and child (1-2 day old calf)

Zebu, Mbane, Senegal Photo credit: Huyse T et al. PLoS Pathog. 2009 Sep;5(9):e1000571. Epub 2009 Sep 4. (PMID: 19730700)

Why cows are sacred in Hinduism? Cow and Proud Owner in Dacca, Bangladesh Photo credit: Dobson A et al. PLoS Med. 2006 Jun;3(6):e231.(PMID: 16729846) We do not know exactly why cows are sacred in parts of India. They have been considered sacred since the Aryans invasion in the 2nd century, B.C. However, many taboos reflect cultural selection for activities that reduce disease risk. A variety of historical papers have suggested that sleeping in close proximity to livestock may decrease the rate at which mosquitoes bite humans, and thus reduce the likelihood of infection with malaria and other vector-borne pathogens (the phenomenon was termed zooprophylaxis). Active zooprophylaxis was undertaken when cattle were deliberately used as a barrier between mosquito breeding sites and human settlement; it was probably most widely used in Soviet collective agriculture and is being used in Tanzania today.

References

PubMed articles

• Bahna SL. Cow's milk allergy versus cow milk intolerance. Ann Allergy Asthma Immunol. 2002 Dec PMID: 12487206
• Drackley JK. Calf nutrition from birth to breeding. Vet Clin North Am Food Anim Pract. 2008 Mar PMID: 18299032
• Hiendleder S, Lewalski H, Janke A. Complete mitochondrial genomes of Bos taurus and Bos indicus provide new insights into intra-species variation, taxonomy and domestication. Cytogenet Genome Res. 2008 PMID: 18467841
• Dobson H, Kamonpatana M. A review of female cattle reproduction with special reference to a comparison between buffaloes, cows and zebu. J Reprod Fertil. 1986 May;77(1):1-36. PMID: 3522889
• Beja-Pereira A. et al. The origin of European cattle: evidence from modern and ancient DNA. Proc Natl Acad Sci U S A. 2006 May 23 PMID: 16690747
• Isaac E. On the Domestication of Cattle: Zoology and cultural history both illuminate the view that the original motive was religious, not economic. Science. 1962 Jul 20;137(3525):195-204. PMID: 17801107
• Buntjer JB et al. Phylogeny of bovine species based on AFLP fingerprinting. Heredity. 2002 Jan;88(1):46-51. PMID: 11813106
• Edwards CJ et al. Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs. Proc Biol Sci. 2007 Jun 7;274(1616):1377-85. PMID: 17412685
• Edwards CJ et al. Taurine and zebu admixture in Near Eastern cattle: a comparison of mitochondrial, autosomal and Y-chromosomal data. Anim Genet. 2007 Oct;38(5):520-4. PMID: 17725685
• Loftus RT et al. Evidence for two independent domestications of cattle. Proc Natl Acad Sci U S A. 1994 Mar 29;91(7):2757-61. PMID: 8146187
• Ritz LR et al. Phylogenetic analysis of the tribe Bovini using microsatellites. Anim Genet. 2000 Jun;31(3):178-85. PMID: 10895308
• Dobson A et al. Sacred cows and sympathetic squirrels: the importance of biological diversity to human health. PLoS Med. 2006 Jun;3(6):e231. PMID: 16729846

Websites

• T. van Vuure. HISTORY, MORPHOLOGY AND ECOLOGY OF THE AUROCHS (BOS PRIMIGENIUS).
• Free full text articles in PubMed: major topic "Cattle"
• Animal Diversity Web: Bos taurus
• Costello R. Bloat in young calves and other pre-ruminant livestock.
• Digestive physiology of herbivores.
• Mammary Gland Development Involution
• Cattle Embryo Growth, Development and Viability

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