Genomic PTA's Are Coming In 2009
Dairy Pipeline: November 2008
Extension Dairy Scientist,
Genetics & Management
(540) 231-4762, firstname.lastname@example.org
I saw my first Genomic PTA’s today – October 15, 2008. A producer shared genomic proofs on a bull from a flush for an AI stud. Some genomic PTA’s are available to animal owners today, and will be released by USDA to the public for the first time in January 2009.
These genetic evaluations are predictions of genetic merit for different traits based on “dense SNP array” data from tissue samples on the animals being evaluated. A SNP or “single nucleotide polymorphism” is a change in a nucleotide—A:T or C:G—in DNA. Based on questions I have heard, there is a good deal of misunderstanding about genomic PTA’s.
Genomic data improves the accuracy of predictions of genetic merit over pedigree information alone, but the evaluations are still imperfect predictions. They are better than the pedigree data has been because they are based on the DNA animals actually inherit from parents. Parent average, which is the traditional pedigree estimate of genetic merit, predicts the expected average genetic merit of progeny of a sire - dam combination. But each individual offspring of such a mating gets a different gene sample from the average. For example, the evaluation that I saw today showed a Genomic PTA of 1.9 for daughter pregnancy rate on the bull calf, while his Parent Average was 1.3. This bull had inherited a slightly above average gene sample from his sire and dam, or maybe those PTA’s were lower than they should have been. The Reliability of the Genomic PTA for DPR was 55%, by no means a “highly reliable” proof, but certainly higher than the Reliability of 26% based on Parent Average.
I recently heard the first of what will certainly
be a number of new marketing ideas
using Genomic PTA’s. A “bundle” of semen
consisting of equal amounts (10 or more
units per bull) of sex sorted semen on three
bulls would be sold. The bulls would be three
year olds, still two years away from progeny
test results. As I understand the plan, the
average Genomic PTA of the three bulls will
be published, rather than proofs on individuals,
as the individual proofs are not of equal
accuracy to proven bulls. The idea is for producers
to be able to use sexed semen from
young bulls with better prospects for high genetic
merit than if the bundle had been selected
on parent average. I like this concept.
It would offer sexed semen on bulls that
should be of exceptional genetic merit. It also
spreads out the risk of change in proofs on
individual bulls where the Reliabilities don’t
justify heavy use of single individuals.
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