Major changes in genetic evaluations of dairy cows don’t come along every day. Producers notice the genetic base changes every five years. “We have recently added traits to the indexes like Net Merit (NM$) because it made sense to do so,” explains Bennet Cassell, Virginia Tech extension dairy genetics and management specialist.
These changes use systems that have been in place for some time. Over the past year, however, a fundamental change has been under way. A new kind of information about genetic merit of dairy cows has become available and is being integrated into genetic evaluations.
The information comes from a technology called “dense SNP arrays.” The device that measures all these SNPs is called the Illuminia Bovine SNP50 beadchip. What this technology does is reveal the genetic makeup of individual animals at about 50,000 locations in their DNA.
“Many important phenotypes, or characteristics we directly observe such as milk records on daughters of a bull, are only available when the animal is older,” says Cassell. Phenotypic information becomes more useful in predicting genetic merit of an animal over time since more records accumulate either on the maturing animal or on its progeny.
Dense SNP array technology uses blood, tissue, hair, or semen samples. Only a single sample is needed in the life of an animal, but the test costs about $250 per animal. This isn’t a test that most dairy farmers would be willing to use on a whole herd, at least at this stage, Cassell notes. It has been used on AI bulls of historic importance as well as currently active AI sires and young bulls in AI sampling programs.
Dairy males can only be genotyped if sponsored or nominated by a major AI organization because of proprietary control of the technology. This exclusivity for bulls will be in effect until 2013.
However, dairy females may be genotyped by individual owners. The tests have been performed on a growing number of potentially elite females in the Holstein, Jersey and Brown Swiss breeds. Some high-end purebred sales have begun to feature genomic-tested females, and sales prices are beginning to reflect the results of those tests, says Cassell.
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