New DNA Bank Promises To Improve Cattle Breeding

The sites along the DNA sequence that show variation among animals are called polymorphisms. This term is becoming widely used as genomic technologies begin to play an increasingly important role in animal breeding. Differences in even one nucleotide, or single nucleotide polymorphism (SNP – pronounced ‘snip’), can result in a change in expression level of the gene or a change in function of the gene product. Such changes can affect the performance of the animal.

The challenge and opportunity, is to identify the genetic basis or SNPs controlling economically important traits such as growth rate, feed efficiency, animal health, fertility and milk production, and to integrate the favourable allele into the commercial cattle population.

A DNA bank resource for Irish dairy and beef cattle is currently being established at Teagasc. To date, protocols for the extraction and storage of DNA from blood, semen and other tissues have been evaluated, optimised and standardised. DNA from more than 6,500 cattle has been extracted, including dairy and beef AI sires as well as the Teagasc dairy research herds. Currently, 4,500 dairy cows from several different breeds are represented in this DNA bank. Research will generally involve three steps: 1) identification of genetic differences among animals at the DNA level; 2) quantification of the association between the identified genetic variants and traits of importance in cattle, and validation of these results in independent populations; and, 3) exploitation of the results in a breeding programme.

For example, if a ‘beneficial’ genetic variant is identified, then animals possessing this variant can be included by breed organisations or breeders in subsequent breeding programmes. Appreciation of this fact has led to the development of the concept of ‘genomic selection’. Genomic selection involves simultaneous estimation of the associations between thousands of SNPs and economically important traits, and the selection of animals that have the best ‘DNA signature’ across the thousands of SNPs.

The research underpinning genomic selection for Irish dairy cattle is currently underway at Teagasc, Moorepark, in conjunction with the national dairy cattle breeding programme, and is being implemented this Spring. The Teagasc DNA bank is fundamental to the development of the genomic selection breeding programme for Ireland. To date, over 1,000 Holstein-Friesian dairy sires, whose DNA was extracted from semen, have been genotyped.

This population will act as the foundation population for estimating the SNP associations. Genomic selection is particularly useful for young animals and for traits that are associated with gender (e.g., milk yield can only be measured in females), traits that take a long time to measure (e.g., measures of daughter survival to fourth lactation are only available when a bull is at least seven years of age), traits where there are considerable management effects or errors in recording (e.g., fertility), and traits that are difficult to measure (e.g., feed efficiency).

Research from Ireland suggests that genomic selection will increase genetic gain by 50%, or in other words, an increase in annual rate of genetic gain in Economic Breeding Index (EBI) in dairy cows from €23/year to €35/year, which is worth €2.5m annually to the dairy industry and is cumulative and permanent.

This study was featured in 'TResearch', Volume 4, Number 1, Spring 2009.