Bovine sequencing brings out the best

RED DEER – It made sense to follow up the human genome study with a bovine project because of the close genetic connection between humans and cattle, says Holstein Canada’s breed improvement manager.

“The human and bovine go back to a common ancestor so the (genetic) architecture has been conserved,” Jay Shannon told the Western Dairy Seminar in Red Deer March 12.

The technology to sequence genomes is constantly evolving. The human genome project took 13 years and cost $3 billion.

The bovine genome took place over six years involving 25 countries and cost $53 million.

The first bovine under the scanner was an inbred eight-year-old Hereford cow named L1 Dominette 01449. Other breeds were compared so that scientists could trace the evolution of cattle and the points where changes occurred.

Researchers found that fewer than 100 animals contribute unique genes in the Holstein breed worldwide. They also found 40 percent more variation in Angus and Holstein breeds than what exists in the human population.

However, Shannon said the subunits of DNA, the nucleotides, are diverse enough in the Holstein breed to make further genetic improvement possible.

DNA is composed of three billion nucleotides arranged over the chromosome pairs contributed equally by the parents. The DNA provides all the instructions needed for cell functions.

The building blocks of DNA have the chemical basis of adenine, thymine, guanine and cystosine, known as A,T, G and C on the code. Probably 99.9 percent of the code is the same for any two individuals.

The differences appear in a single nucleotide polymorphism known as a SNP, pronounced snips. These markers indicate a nucleotide location where variation exists in the population.

As more bulls are tested and larger SNPs become available, the accuracy of genetic predictions will improve because these are like road maps to specific traits, Shannon said.

Scientists have identified 2.44 million SNPs on the bovine genome out of a total five million. Humans may have about 10 million.

He said a tool like this works well for the dairy industry because every trait has already been measured.

Most recently, the University of Alberta sequenced an Angus bull and a Holstein bull. The study took seven months and cost $65,000. Part of the study found more than 4.6 million genetic mutations; most were previously unknown.

Running genomic sequences on Holstein bulls makes sire selection easier.

Seven artificial insemination companies in North America, including Alta Genetics and Semex, are working with the U.S. Department of Agriculture to test Holstein bulls.

About 1,000 Canadian bulls have been evaluated, looking at their ability to pass on good body conformation, proper mammary system, daughter fertility and high milk production.

The more bulls that are tested, the more reliable the data will become. As well, the price of the tests is coming down so more herds will be able to use this technology. 

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