Managing Genetic Defects

Managing Genetic Defects

By Montie Soules

Genetic defects are not a new phenomenon. What is new is the technology of using DNA markers associated with the defects to give cattle breeders the ability to identity and manage these problems when they appear.  I'm going to give you my personal viewpoint in layman's terms, as a non-expert, of why we have genetic defects and where they come from.

My most important message is that I believe defects can be managed with minimal impact. These problems are not the downfall of a herd or breed, if they are identified and managed with responsibility. We are fortunate to now have the technology to identify these problems. We will see more DNA markers discovered that will give us more information to help us be better breeders for genetic traits, changing the way we breed cattle in the future. This technology will provide information about the good traits and the bad traits.

In the 1950s, the Hereford breed as well as other breeds, faced the dwarfism problem. After putting heavy selection for many years on breeding smaller, short legged cattle, the breed and industry had dwarf calves being born from certain bloodlines. There was no DNA test, or even any technology, to accurately identify these defective individuals. Breeders and associations had to trust each other and share information to get the problem cattle identified by breeder observation.

During this time many lines of cattle were wiped out because a small percentage of that line produced a dwarf. Showing the scope of the problem, the Hereford Association pedigree examiner examined as many as 59,000 registration papers in just one year to identify cattle lines that had been known to produce a dwarf calf. The breeders took care of the dwarf problem with the cooperation of the association, although it was into the '60s before the issue was considered behind the breed. As a small boy, I remember the conversations with breeders about dwarfism.

I remember seeing my first Hypotrichosis (HY, short hair) calf born around 1990. There was little more technology at that time to identify a calf with this condition than there had been for dwarfism. It again fell back to the breeders' responsibility to share information and identify the cattle that carried this genetic defect by reporting calves displaying the defect. The association, with accurate identification, listed animals with the problem.  By mating animals from the problem bloodlines only to ones we thought were not carriers, we as breeders pretty well eliminated the problems within a few years.

The lingering problem was that HY was not totally eliminated, and a handful of affected individuals still showed up every now and then. There had been no test to accurately identify the free and carrier cattle. The diluter gene (DL) showed up about the same time with the same experiences. Then a few years back, the Idiopathic Epilepsy gene (IE) showed up. By this time there had been enough DNA breakthroughs that the extra time and energy was put into identifying the IE gene through DNA. The phenomenon of genetic defects is not isolated to Hereford cattle.  Most beef breeds have experienced similar issues with genetic defects within their own breeds. 

The curiosity is where do these genetic defects come from? It is my understanding a defect is a mutation that takes place in the genes or chromosomes of an animal as it is being developed from conception. What causes this mutation to take place? Through my conversations and questions and reading articles by people that are experts in this area, it is my conclusion and observation that the genetic defects are the possible result of high pressure in our selection process when mating animals with the same strong trait and then stacking this for generations.

In theory, you could almost forget about the bloodline or names of animals. Look at single trait selection for generations and a mutation falls out as a recessive gene. Later, when continued selection pressure is used in mating for that single trait, the genetic defect becomes a reality and an affected calf is born.  A number of problem calves may be born because of the concentrated mating pressure for that trait from both sire and dam and from their genetic heritage.  In actuality, the number of calves born with a problem is a small segment of the cattle population as these genetic defects are a recessive gene.  If a seedstock breeder or commercial breeder gets the genetics lined up with the recessive trait defects coming from both sides of the pedigree, though, the results could be quite disastrous with numerous affected calves being born.

How do we manage these genetic defects?  My view and the one we are taking at Star Lake is that it is a breeder's responsibility to identify individuals with problems and then manage them accordingly. At Star Lake we have tested all the herd sires and donor cows for three genetic defects (IE) (DL) (HY).  It is our policy to not knowingly sell any genetic defect carrier, which would be identified on the registration certificate with (IEC) (DLC) and/or (HYC).  

Breeder responsibility is essential to control and manage these problems. If we have a cow that is a carrier and she is good enough, we will continue to breed her to free bulls and test the progeny. We then go forward to make breed improvement with her progeny that test free for the genetic defect. To throw away superior individuals that can make a positive impact on breed improvement is not necessary today with the DNA test. 

DNA markers are not used only to identify problems. Everyone should understand that DNA markers will help us find traits that will enhance our breed improvement. They will be most beneficial when they will isolate positive traits such as efficiency, marbling, REA, disposition, calving ease, etc.  The possibilities are endless.

Star Lake will use herd sires tested free of known genetic defects in our program (IEF) (DLF) and (HYF). By mating free cows to free bulls, the resulting calves will be free unless the very rare mutation occurs. This goes back to the description of selection pressure for a single trait.

At Star Lake we have boasted about balanced EPDs and balanced phenotype for a number of years. Our mating selections will continue to keep the data in a balanced form and not try to breed for freaks in any one area. We learned in the '80s, when the rush was on in our industry for big framed cattle, that many negatives came with that single trait selection. 

Even with all the science, tools and technologies available, there is still a place in the seedstock business for common sense in our breeding programs. At Star Lake, we are committed to maintaining our responsibility as a Hereford seedstock breeder.  And we will use tools and technologies along with common sense to design that balanced, high quality Star Lake Hereford.