Genetic Visions Inc.®
www.geneticvisions.net | 608-662-9170 | info@geneticvisions.com
DNA Tools Coming Of Age
By Dr. C. Michael Cowan Vice-President Research Accelerated Genetics and General
Manager Genetic Visions Inc.
The popular Crime Scene Investigation "CSI" TV series dazzles viewers
by solving the seemingly unsolvable, uncovering the smallest piece of evidence which
leads to the culprit and brings the crime to resolution; often by the unique characteristics
of DNA. While not as dramatic as these popular shows, the tools used to detect and
define the characteristics of DNA play an ever growing role in the AI industry.
Modifications in the basic building blocks of DNA are used as selection tools, in
animal identity and traceability, in detection of undesirable genes, accessing the
caliber of young sire progeny test herds, as an added quality control in semen processing
and provides the foundation for research projects that will expand our understanding
genetic and environmental factors.
Many dairy and beef producer are aware of DNA tests that focus on a single gene.
Black/Red coat color, BLAD, CVM, and DUMPs are examples. Blood, hair or semen provide
a DNA source which quickly answers if an individual carries a copy of the red coat
color allele or whether an animal has a known lethal recessive gene. Lets explore
some other applications of DNA tools in our industry.
Accelerated Genetics invests significant time and funds testing each young sire.
When a young bulls arrives to enter isolation is it the one we selected from the
farm? Sometimes not, mistakes happen. A sample of the first semen collected is genotyped
again and the results compared with those obtained on the farm. The results should
match, confirming it is the same animal tested previously.
When semen is released for young sire progeny testing, the sire misidentification
rate in test herds can greatly influence the outcome. Daughters of the most promising
young sires in herds with high sire misidentification rates are more likely to be
labeled as offspring of a different sire and vice versa. This tends to make all
animals appear more alike than they really are. Resulting in genetic evaluations
of bulls with truly high genetic merit being under estimated while low genetic merit
bulls tending to be over estimated. Ideally, eliminating all the sire identification
errors will result in the most accurate evaluation. Attempting to remove all the
sire identification error for all young sires tested is not practical nor economical.
However, when herd heritability is negatively impacted the herd is a candidate for
a review as a test herd. Accelerated Genetics has used DNA to spot check progeny
test herds for many years. New DNA techniques now afford a means to rapidly screen
a large number of animals.
Quality control. While there are many checks and cross checks in the semen processing
procedures, occasionally questions arise regarding the semen contents of a straw.
If so, DNA from a straw can be compared with DNA from the animal’s blood or other
semen from the same bull. Apart from identical twins each bull has his own unique
DNA marker pattern. By running a series of DNA markers, cells in the semen straw
should match the DNA patterns of a know source, if correct.Bulls that are twins
are in AI programs. Roughly 90% of cattle twins are chimeras, contain a mixture
of blood stem cells from its’ fraternal twin. When determining parentage or conducting
some other type of DNA tests on fraternal twins, it is important to use a DNA source
other than blood to get a true genotype. DNA techniques have the power to detect
very small amounts of added DNA. For example, when heifer blood is tested for the
Freemartin condition, blood samples containing 1% or less male DNA readily produce
a positive result. An AI organization’s future depends on its young sire program,
find the most promising young bulls, then confirm their genetic potential by accurate
progeny evaluations. Pedigree selection has been the primary tool. Accelerated Genetics and Genetic Visions have shown that a single DNA marker linked to traits such as
milk or component yield can improve the chances of finding superior young sires
beyond pedigree selection alone. Moreover, DNA marker selection is the only way
to distinguish between full siblings. However, most of our current knowledge and
experience focuses on associations largely within individual sire families. Larger
genome-wide studies are needed to broaden marker-assisted selection in cattle. The
bovine genome is the most complete and accurate genome sequenced to date. This data
has been used to find ten of thousand of single nucleotide polymorphisms, SNPs.
Researchers at the USDA Functional Genomics Lab and a company that develops kits
for genetic research have teamed to produce a device that can genotype samples with
up to 60,000 SNPs. Currently, bovine genome-wide screens of several thousand bulls
used in AI are underway. The goal is create a SNP map for each chromosome and to
develop new methodologies for genetic evaluations; which incorporates marker data
for those SNPs linked to economic traits. Eventually formulating a "DNA marker
adjusted pedigree estimate" for individual animals. Armed with this new information
it may be possible to double our accuracy of predicting the true level of genetic
value of an animal before progeny test or performance testing. As such, the greatest
value of DNA techniques may lie with estimating the contribution from the female’s
genome.DNA technologies are not just a good story line for TV. As our knowledge
and availability of new tools increases, DNA technologies will become increasingly
common place in the dairy and beef industry.