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Breeding and Genetics

Trends in Dairy Cattle Breeding and Genetics By Dennis Johnson

The number of tools to develop a productive and profitable dairy herd that is genetically superior continues to grow. All of the old methods, such as crossbreeding or selection, are still available and new information is coming from biotechnology. The latest aid comes from the new science of genomics. Genomics is the mapping and sequencing of genetic material in the DNA of a particular organism. As genomics becomes more sophisticated, it may actually identify genes and their role. But even now, it may be utilized to increase the effectiveness of sire evaluation. DNA provides the set of instructions (genes) that a cow needs in order to grow, produce milk, breed back, etc. Some parts of the DNA dictate the structure of proteins. Other sections of DNA tell genes

when to turn on or turn off and are the media for transmitting genetic information from one generation to the next. Some sections of DNA appear to have little or no useful function. Genomic selection is the new tool. Over the past several years,

Over time, selection of bulls on Lifetime Net Merit should lead to cattle that continue to improve in production but are also healthier over a lifetime. DNA has been saved from about 15,000 bulls used in AI. The DNA has been analyzed to identify the 50,000+ sites of single nucleotide polymorphism (SNP - say “snip�) markers located on the 30 chromosomes of the bovine genome. Each

marker site may have two of four base variants. There are about 3 billion SNPs in the genome of the cow, but the current technology identifies enough sites to give an animal a unique pattern of SNPs. Furthermore, the pattern of base pairs can be compared with the pattern of outstanding ancestors to predict the breeding merit of the animal. Up until now, the breeding merit of young bulls has been estimated from the average genetic merit of its parents derived by using DHIA records in progeny testing. But now the accuracy of breeding merit can be improved by incorporating information from the SNP scan with the accumulated transmitting ability of parents to create a genomic index. Thus, a young bull with a genomic index, but no tested * Continued on page 18

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December 2017

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American Dairymen - December 2017  
American Dairymen - December 2017