Meat is animal tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of animals, including chickens, sheep, goats, pigs, horses, and cattle, starting around 11,000 years ago. Since then, selective breeding has enabled farmers to produce meat with the qualities desired by producers and consumers.
Meat is mainly composed of water, protein, and fat. Its quality is affected by many factors, including the genetics and nutritional status of the animal involved. It is edible raw, but is normally eaten cooked, such as by stewing or roasting, or processed, such as by smoking or salting. Bacteria and fungi decompose and spoil unprocessed meat within hours or days.
Meat Png
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The consumption of meat, especially red and processed meat, causes health effects including increased risks of cancer, coronary heart disease, and diabetes. Meat production is a major contributor to environmental issues including global warming, pollution, and biodiversity loss, at every scale from local to global.
Meat is important to economies and cultures around the world. Some people choose not to eat meat (vegetarians) for reasons such as ethics, environmental effects, health concerns, or religious dietary rules.
The word meat comes from the Old English word mete, meaning food in general. In modern usage, meat primarily means skeletal muscle with its associated fat and connective tissue, but it can include offal, other edible organs such as liver and kidney.[1] The term is sometimes used in a more restrictive sense to mean the flesh of mammalian species (pigs, cattle, sheep, goats, etc.) raised and prepared for human consumption, to the exclusion of fish, other seafood, insects, poultry, or other animals.[2][3]
English has specialized terms for the meat of particular animals, deriving from the Norman conquest of England in 1066: while the animals retained their English names, their meat as brought to the tables of the invaders was named in Norman French. These names came to be used by the entire population.[4]
Paleontological evidence suggests that meat constituted a substantial proportion of the diet of the earliest humans. Early hunter-gatherers depended on the organized hunting of large animals such as bison and deer. Animals were domesticated in the Neolithic, enabling the systematic production of meat and the breeding of animals to improve meat production.[1]
In the postwar period, governments gave farmers guaranteed prices to increase animal production. The effect was to raise output at the cost of increased inputs such as of animal feed and veterinary medicines, as well as of animal disease and environmental pollution.[8] In 1966, the United States, the United Kingdom and other industrialized nations, began factory farming of beef and dairy cattle and domestic pigs.[9] Intensive animal farming became globalized in the later years of the 20th century, replacing traditional stock rearing in countries around the world.[9] In 1990 intensive animal farming accounted for 30% of world meat production and by 2005, this had risen to 40%.[9]
Meat production continues to be shaped by the demands of customers. The trend towards selling meat in pre-packaged cuts has increased the demand for larger breeds of cattle, better suited to producing such cuts.[10] Animals not previously exploited for their meat are now being farmed, including mammals such as antelope, zebra, water buffalo and camel,[10] as well as non-mammals, such as crocodile, emu and ostrich.[10] Organic farming supports an increasing demand for meat produced to that standard.[11]
Some economically important traits in meat animals are heritable to some degree, and can thus be selected for by animal breeding. In cattle, certain growth features are controlled by recessive genes which have not so far been controlled, complicating breeding.[12] One such trait is dwarfism; another is the doppelender or "double muscling" condition, which causes muscle hypertrophy and thereby increases the animal's commercial value.[12] Genetic analysis continues to reveal the genetic mechanisms that control numerous aspects of the endocrine system and, through it, meat growth and quality.[12]
Genetic engineering techniques can shorten breeding programs significantly because they allow for the identification and isolation of genes coding for desired traits, and for the reincorporation of these genes into the animal genome.[12] To enable such manipulation, the genomes of many animals are being mapped.[12] Some research has already seen commercial application. For instance, a recombinant bacterium has been developed which improves the digestion of grass in the rumen of cattle, and some specific features of muscle fibers have been genetically altered.[12] Experimental reproductive cloning of commercially important meat animals such as sheep, pig or cattle has been successful. Multiple asexual reproduction of animals bearing desirable traits is anticipated.[12]
Heat regulation in livestock is of economic significance, as mammals attempt to maintain a constant optimal body temperature. Low temperatures tend to prolong animal development and high temperatures tend to delay it. Depending on their size, body shape and insulation through tissue and fur, some animals have a relatively narrow zone of temperature tolerance and others (e.g. cattle) a broad one. Static magnetic fields, for reasons still unknown, retard animal development.[13]
The quality and quantity of usable meat depends on the animal's plane of nutrition, i.e., whether it is over- or underfed. Scientists disagree about how exactly the plane of nutrition influences carcase composition.[14]
The composition of the diet, especially the amount of protein provided, is an important factor regulating animal growth. Ruminants, which may digest cellulose, are better adapted to poor-quality diets, but their ruminal microorganisms degrade high-quality protein if supplied in excess. Because producing high-quality protein animal feed is expensive, several techniques are employed or experimented with to ensure maximum utilization of protein. These include the treatment of feed with formalin to protect amino acids during their passage through the rumen, the recycling of manure by feeding it back to cattle mixed with feed concentrates, or the conversion of petroleum hydrocarbons to protein through microbial action.[14]
In plant feed, environmental factors influence the availability of crucial nutrients or micronutrients, a lack or excess of which can cause a great many ailments. In Australia, where the soil contains limited phosphate, cattle are fed additional phosphate to increase the efficiency of beef production. Also in Australia, cattle and sheep in certain areas were often found losing their appetite and dying in the midst of rich pasture; this was found to be a result of cobalt deficiency in the soil. Plant toxins are a risk to grazing animals; for instance, sodium fluoroacetate, found in some African and Australian plants, kills by disrupting the cellular metabolism. Some man-made pollutants such as methylmercury and some pesticide residues present a particular hazard as they bioaccumulate in meat, potentially poisoning consumers.[14]
Practices such as confinement in factory farming have generated concerns for animal welfare. Animals have abnormal behaviors such as tail-biting, cannibalism, and feather pecking. Invasive procedures such as beak trimming, castration, and ear notching have similarly been questioned.[18] Breeding for high productivity may affect welfare, as when broiler chickens are bred to be very large and to grow rapidly. Broilers often have leg deformities and become lame, and many die from the stress of handling and transport.[19]
Growth hormones, particularly anabolic agents such as steroids, are used in some countries to accelerate muscle growth in animals.[20] This practice has given rise to the beef hormone controversy, an international trade dispute. It may decrease the tenderness of meat, although research on this is inconclusive, and have other effects on the composition of the muscle flesh.[21] Where castration is used to improve control over male animals, its side effects can be counteracted by the administration of hormones.[20] Myostatin has been used to produce muscle hypertrophy.[22]
Sedatives may be administered to animals to counteract stress factors and increase weight gain. The feeding of antibiotics to certain animals increases growth rates. This practice is particularly prevalent in the US, but has been banned in the EU, partly because it causes antimicrobial resistance in pathogenic microorganisms.[21]
The biochemical composition of meat varies in complex ways depending on the species, breed, sex, age, plane of nutrition, training and exercise of the animal, as well as on the anatomical location of the musculature involved.[23] Even between animals of the same litter and sex there are considerable differences in such parameters as the percentage of intramuscular fat.[24]
Meat can be broadly classified as "red" or "white" depending on the concentration of myoglobin in muscle fiber. When myoglobin is exposed to oxygen, reddish oxymyoglobin develops, making myoglobin-rich meat appear red. The redness of meat depends on species, animal age, and fiber type: Red meat contains more narrow muscle fibers that tend to operate over long periods without rest,[27] while white meat contains more broad fibers that tend to work in short fast bursts, such as the brief flight of the chicken.[27] The meat of adult mammals such as cows, sheep, and horses is considered red, while chicken and turkey breast meat is considered white.[28]
Muscle tissue is high in protein, containing all of the essential amino acids, and in most cases is a good source of zinc, vitamin B12, selenium, phosphorus, niacin, vitamin B6, choline, riboflavin and iron.[29] Several forms of meat are high in vitamin K.[30] Muscle tissue is very low in carbohydrates and does not contain dietary fiber.[31] 152ee80cbc