ancestor is the now extinct auroch; sheep derived from the Asiatic mouflon species; goats, which are descended from the benzoar goat of West Asia; pigs derived from captured wild boars; and horses, which originated from now extinct wild horses that roamed the steppes of Southern Russia) are found worldwide (Diamond, 1999; Box 1.2). As pointed out by Hale (1969) and Diamond (1999), the animals that have been successfully domesticated and farmed share and exhibit a unique combination of characteristics. They are relatively docile, are flexible in their dietary habits, and can grow and reach maturity quickly on a herbivorous diet, and breed readily in captivity. They also have hierarchical social structures that permit humans to establish dominance over them, and are adapted to living in large groups. They do not include species that generally have a tendency to be fearful of humans or disturbed by sudden changes in the environment. Our ancestors no doubt based their selection methods for improving their herds and flocks on how easy the animals were to farm, as well as on potential agricultural value. In turn, the animals are adapted to thrive in a domesticated environment.

BOX 1.2 Progression of Technologies Incorporated into Modern Animal Agriculture1

Vaccinations and other health technologies2

Artificial insemination3

Freezing of semen4

Sire testing and selection5

Use of antibiotics in feed to increase gain6

Embryo transfer7

Embryo splitting and cloning from blastomeres8

In vitro maturation/in vitro fertilization of oocytes and in vitro culture of resulting embryos

Use of hormones to control ovulation in farm animals and to induce spawning in fish zygotes9

Hormonal sex reversal and production of monosex fish stocks

Chromosome set manipulation10

Steroid administration to improve weight gain

Bovine somatotropin (BST) to increase milk production in dairy cows

Marker-assisted selection

1  

Technologies are presented in approximate sequential order of adoption; several technologies (such as artificial insemination, which was first described in 1910 but not widely adopted until the 1950s) were developed years or decades before they were commonly used.

2  

Vaccination is used widely in the livestock and poultry industries as a protection against viral and bacterial pathogens.

3  

Artificial insemination (AI)—in conjunction with the use of frozen semen from select bulls— is common in the dairy industry but relatively rare in the U.S. beef industry. The use of fresh semen for AI is becoming increasingly important in the swine and poultry industries.

4  

Bovine semen can be successfully frozen to yield high-quality, motile sperm upon thawing. The freezing of semen is problematic for swine and other livestock.



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