Methods of ranking animals for breeding purposes have changed as statistical and genetic knowledge has increased. Along with increases in breeding knowledge, advancements in computing have enabled breeders to quickly and easily process routine breeding evaluations, as well as to develop research needed to rank large populations of animals. Evaluating and ranking candidates for selection depends on equating their performance record to a statistical model. A performance record (y) can be expressed asy = g + e + ε,where g stands for genetic effects, e indicates known (categorized) environmental effects, and ε indicates random environmental effects.
The first task in estimating g is to statistically eliminate environmental effects, a process that involves setting up a system of equations to simultaneously solve for all of the genetic effects for the sires and cows. Information from relatives is included in g and increases the accuracy of evaluation of the candidates for selection. All relatives that are available can be incorporated in this type of evaluation. This model is called the animal model.
The animal model is used extensively in evaluating beef and dairy cattle, chickens, and pigs. To apply this model for evaluating large populations requires use of high-speed computers and extensive use of advanced mathematical techniques from numerical analysis. In evaluating the dairy cattle in the United States, a system of equations with more than 25 million variables is needed.
Red-Poll-cow-and-calfRed Poll cow and calf.[Credits : © J.C. Allen and Son]
Thoroughbred-stallion-with-dark-bay-coatThoroughbred stallion with dark bay coat.[Credits : © Scott Smudsky]
The-mouse-at-bottom-is-heterozygous-with-a-mutant-geneThe mouse at bottom is heterozygous with a mutant gene that gives it a spotted tail. The two mice …[Credits : Inserm U636]
Black-Angus-bullBlack Angus bull.[Credits : Henry Elder/Encyclopædia Britannica, Inc.]
Female-pigs-can-have-as-many-as-20-piglets-inFemale pigs can have as many as 20 piglets in a litter. China holds the record for having the …[Credits : © Corbis]
German-shepherdGerman shepherd (Alsatian).[Credits : © Sally Anne Thompson/Animal Photography]
Holstein-Friesian-cowHolstein-Friesian cow.[Credits : Henry Elder/Encyclopædia Britannica, Inc.]
Duroc-boarDuroc boar.[Credits : Grant Heilman Photography]
Link to this article and share the full text with the readers of your Web site or blog-post.
If you think a reference to this article on "animal breeding" will enhance your Web site,
blog-post, or any other web-content, then feel free to link to this article,
and your readers will gain full access to the full article, even if they do not subscribe to our service.
You may want to use the HTML code fragment provided below.
We welcome your comments. Any revisions or updates suggested for this article will be reviewed by our editorial staff. Contact us here.
Regular users of Britannica may notice that this comments feature is less robust than in the past. This is only temporary, while we make the transition to a dramatically new and richer site. The functionality of the system will be restored soon.