Here's the bitter pill. Every living thing – including you – carries a large number of broken genes. In humans, on average, we carry one broken, lethal copy and one normal copy of about 20 genes. In other words, if we had inherited two copies of the broken gene, we wouldn't have survived past birth.
We have about another 80 genes for which one copy is broken, but it’s not lethal. These 80 cause some sort of abnormality or defect if we were to inherit two copies, but do not result in death. The same situation is true for our cattle.
Dorian Garrick, Lush Chair of Animal Breeding & Genetics at Iowa State University, gave a great presentation on this topic at the Beef Improvement Federation meeting in June. Find a summary, proceeding paper, slides, and audio here. Garrick argued that knowing our animal is a carrier is a good thing, because now we are dealing with a known rather than an unknown. He said a new perspective about genetic defects was needed.
Garrick also pointed out that all animals are carriers of something. For example, I recently saw cattle advertised as "100% genetic defect free." The breeder did not realize this, but this statement is patently untrue, and is actually false advertising. The breeder could have stated that the animals are 100% free of known genetic defects, but all animals carry genetic defects.
These scientific facts force us to change the way we view and approach genetic abnormalities and defects. Cattle producers and breed associations cannot rapidly eliminate genetic defects. If they do so, valuable animals with superior genetic merit for production traits will be discarded. Actually, if they eliminated all carriers, there would be no cattle left of the breed!
Rather, genetic defects need to be managed and gradually selected out of the population. By knowing the carrier status of at-risk animals, we can make certain that we never mate two carriers. By doing so, we will increase pregnancy rates and ensure animal welfare.
Certain breed associations allow their membership to manage genetic defects. These associations allow producers to register, sell, and transfer carrier animals and their progeny. Other breed associations will need to permanently alter their policies to deal with our increased awareness of genetic defects. However, we need to discard the stigma attached to the words “genetic” and “defect.” Hopefully these more favorable policies toward defects will increase the rates of reporting abnormal calves.
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Do not dismay, there is a silver lining to all of this. Due to improvements in DNA genotyping and drastic reductions in the cost of DNA sequencing, researchers can now rapidly identify the DNA variant responsible for a genetic abnormality.
In fact, Dave Patterson and Jerry Taylor at the University of Missouri are leading an effort to sequence approximately 150 popular sires from nine beef breeds. This research will identify numerous broken genes. This research will allow us to select against genetic abnormalities long before we observe affected calves.
Knowing that all animals carry genetic abnormalities, there is no reason to throw the baby out with the bath water. We need to accept the fact that all cattle carry genetic abnormalities and adjust our breeding practices. We’ll now have the tools to manage genetic defects while continuing to use animals of superior genetic merit.
Editor’s note: For more information about genetic testing and genomic technologies in livestock production, visit Decker’s blog.
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