SELECTIONS - Fall 2001
CVM: Putting it in Perspective
By Chuck Sattler, Program for Genetic Advancement coordinator
 Despite the significant genetic improvement our industry has made, we have yet to breed the perfect cow or bull. It is difficult to
get the right combination of outstanding production, functional type,
consistent reproduction and good health all in one animal. With the
research evidence about Complex Vertebral Malformation (CVM) growing,
now we have another trait to consider as we go about improving
Holstein genetics.
CVM is a lethal genetic defect that was identified in Denmark in
fall 2000. It is found in Holsteins and refers to a combination of
symptoms that include fused or misshapen vertebrae, contracted joints
in the front and rear legs, and reduced body size. Calves affected with
CVM are either aborted or born dead. It appears that they are aborted
about two-thirds of the time, and that the abortions can occur at any
time during gestation. Spinal defects are among the most commonly reported
birth defects, so it is possible to confuse CVM with several other conditions.
An x-ray of the spine usually is needed to confirm the occurrence of CVM.
Recently reported research indicates that CVM is a recessive trait. This
means that a calf needs to inherit a defective gene from both its dam and
its sire to be affected with CVM (See Figure 1). CVM-affected calves can
result only when a carrier cow is mated to a carrier bull. When two carriers
are mated, 75 percent of the calves will be normal with 25 percent affected
with CVM. Calves that have one defective gene are completely normal and
their performance will be unaffected. Animals with one CVM gene are often
called "carriers" because, even though they are normal, they can transmit
CVM to their offspring.
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Figure 1: CVM-affected calves can result only when a carrier cow is mated to a carrier bull, as shown in this example.
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The primary transmitter of CVM is 7HO543 Carlin-M Ivanhoe Bell*BL. More
recently, the CVM gene has been multiplied further through the popular
BELL sons, 7HO2236 Emprise Bell ELTON*BL and SOUTHWIND Bell of Bar-Lee.
These sires were used heavily because of their daughters’ outstanding
performance, thereby increasing the prevalence of CVM. It is estimated that
about 10 percent of Holstein cows are CVM carriers. Based on that, a typical
200-cow herd using typical A.I. sires would have one CVM-affected calf a year.
In August, the Danish researchers announced that they had discovered the gene
that causes CVM. This led to the development of a commercial DNA test for CVM
that now is available for routine use, replacing the less-reliable genetic-marker
test.
Select Sires is in the process of testing its Holstein bulls for CVM. We
first submitted tissue samples for bulls in the lineup, with complete results
to be available by November. As test results are received, they are being posted on www.selectsires.com.
Select Sires also has begun testing young sires that are candidates for the
Program for Genetic Advancement (PGA) or SUPER SAMPLER status. Our goal is to
sample only bulls that have been identified as non-carriers of CVM. In the short
term, we will cull CVM-positive bulls with low parent averages. While our sire
epartment will do all it can to purchase additional genetically superior bulls
to maximize the opportunity to cull CVM carriers, the Select Sires board has
approved the sampling of some high parent-average calves that may be CVM
carriers during a transition phase.
Because of today’s DNA technology, genetic defects are not nearly as scary
as they once were. In the past, the only way to identify carriers was by
reporting affected calves. A sire could be used for years without knowing
he carried an undesirable recessive. With DNA-based genetic tests, carriers
can be identified at a young age, making it easier to manage genetic
conditions like CVM.
Through 7HO191 WAYNE-Spring Fond Apollo*MF, BELL, ELTON and 7HO6250 Ricecrest
EMERSON-ET*BL, history shows that bulls carrying recessives can make valuable
contributions to the breed. That’s why we must keep CVM in perspective. A sudden
and complete eradication of the CVM gene likely would eliminate several genes
that are important to the Holstein population.
The bottom line is that one bad gene doesn’t make the other 10,000 worthless.
Using pedigree information, producers can make controlled matings to avoid
CVM-affected calves. Select Mating Service (SMS) can be a helpful tool for
managing this information to avoid the mating of two CVM carriers.
You can trust that Select Sires will maintain its stringent selection standards
while reducing the frequency of CVM in bulls entering the PGA. The result is
that managing the impact of CVM will become easier for you in the future.
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