Frequently Asked Questions About Complex Vertebral Malformation (CVM)
by Dr. Kent Weigel, Assistant Professor and Extension Specialist in Dairy Cattle Breeding and Genetics, University of Wisconsin-Madison
What is CVM?
Complex vertebral malformation (CVM) is a recessively inherited genetic defect that was discovered last year by Danish scientists. CVM is suspected to cause embryonic deaths, abortions and stillborn calves, some with visible deformities. It is important to recognize that CVM is not new. It has been present in the Holstein breed for many generations, and only the DNA test is new.
How do I know whether I have CVM in my herd?
CVM-affected calves will be aborted or born dead. Abortions due to CVM may happen at any time during gestation. Stillborn calves will typically be born one to two weeks prematurely, and the most noticeable defects are the malformed legs with rigid pasterns. A shortened neck also may be visible. However, a pathological examination usually will be necessary to detect abnormal curvature of the spine, fused vertebrae, and fused or missing ribs. Producers are encouraged to report suspected calves to Holstein Association USA or A.I. representatives. Keep in mind, however, that many CVM-affected calves or fetuses will be lost (much) earlier in the gestation period, and such occurrences rarely will be detected. Further, remember that abortion and stillbirths can occur for reasons other than CVM.
How much could CVM impact my herd?
Although the percentage of cows that are CVM carriers has not yet been well documented, it is likely that most herds will have a few carriers. Several popular sire families have transmitted this defect during the past two or three decades, and the number of carriers in a given herd will depend on past usage levels of these bulls. However, there are effective strategies for limiting the impact of CVM, as discussed below.
Is CVM specific to the Holstein breed, or do all breeds have some carriers?
At this time, CVM has been identified only in the Holstein breed.
Will CVM be a permanent problem for the Holstein breed?
No, its impact will decrease dramatically within the next five years. Modern genetic tools allow us to accurately identify sires and cows that carry CVM through DNA testing, and A.I. organizations will avoid buying young bulls that carry the CVM gene. Therefore, very few CVM-carrier bulls will be available four to six years from now. We've already seen a similar pattern for the BLAD gene; nearly 150 U.S. Holstein bulls carried BLAD 10 years ago and very few carrier bulls are available today.
What can I do to control CVM and other undesirable genetic recessives in my herd?
The first step in controlling genetic defects like CVM is to establish pedigree records for the animals in your herd. Once you've done this, it's relatively easy to avoid mating known carrier bulls to cows whose sire or maternal grandsire is also a carrier, because virtually all A.I. sires will be tested. You can do this by visually inspecting pedigrees, by developing a simple spreadsheet program or by using a computerized mating program (as discussed below).
Would the use of a formal mating program help control CVM in my herd?
Yes, it certainly would. Existing mating programs do a great job of controlling inbreeding, and inbred animals are much more likely to inherit the CVM gene from both sides of the pedigree. In addition, most A.I. organizations will modify their mating programs to check the CVM status of a cow's sire, maternal grandsire and proposed mate(s). But remember, if you don't have accurate sire and maternal grandsire identification for the cows in your herd, then mating programs will be relatively useless.
How do I know which A.I. sires are carriers of CVM?
Many A.I. sires already have been tested, and the remainder soon will be tested as well. Holstein Association USA labels CVM carriers with a "CV" recessive code, while bulls that have tested negative for CVM are labeled as "TV". Most publications, such as A.I. sire catalogs or the Sire Summaries (Red) book will show these codes.
Should I avoid using any known CVM carriers in my herd?
It's probably unwise to "panic" and exclude all CVM carrier bulls from your breeding program. Many bulls that carry the undesirable CVM gene also will carry numerous other genes with positive effects on milk production, component percentages, udders, feet and legs, somatic cell count, and other key traits. If you discard all of these bulls, you may end up using a somewhat mediocre group of bulls instead, just to avoid CVM. As long as you avoid using CVM carriers on cows whose sire and/or maternal grandsire carry CVM, you should be fine. Don't worry about creating too many new carrier females in your herd, because in a few years most of the available A.I. sires will be free of CVM anyway.
What if I don't use A.I.?
The discovery of CVM is yet another reason to avoid non-A.I. "jumper" bulls. Virtually all A.I. sires will be tested for CVM, just as they've been screened for BLAD and other genetic defects. But very few, if any, natural service bulls will be tested. It's likely that one or more of your herd sires in the past was a CVM carrier, and heavy use of a (unknown) carrier bull in your herd could result in many abortions, embryonic deaths and stillbirths.