|Gengler, Nicolas - GEMBLOUX AGRIC UNIV|
Submitted to: Encyclopedia of Dairy Science
Publication Type: Book / Chapter
Publication Acceptance Date: January 22, 2009
Publication Date: April 29, 2011
Citation: Wiggans, G.R., Gengler, N. 2011. Selection: Evaluation and methods. In: Fuquay, J.W, Fox, P.F., and McSweeney, P.L.H., editors. Encyclopedia of Dairy Sciences. 2nd edition. San Diego, CA: Academic Press. p. 649-655. Technical Abstract: Procedures to collect and to analyze data for genetic improvement of dairy cattle are described. Methods of identification and milk recording are presented. Selection traits include production (milk, fat, and protein yields and component percentages), conformation (final score and linear type traits), fitness (mastitis, longevity, and fertility), and calving (dystocia and stillbirth). The genetic evaluation system has evolved from comparing cows with dams to comparing them with contemporaries to the current animal model where contributions of all relatives are considered. Evaluations are expressed relative to a genetic base, which sets the mean and in some cases the standard deviation of evaluations for animals in a base group (for example, animals born in a particular year). Genetic bases usually are adjusted over time to reflect genetic improvement. The Interbull Centre in Sweden combines national evaluations from over 20 countries to provide an international ranking of all bulls on the scale of each participating country. Recent research has focused on using DNA information (single-nucleotide polymorphisms) to estimate genetic merit early in an animal’s life before phenotypic records are available. That technology may substantially enhance the rate of genetic improvement by increasing selection intensity and reducing generation interval with only a small loss in accuracy.