SALEM, Ohio – Dairy industry leaders and artificial insemination companies are urging Holstein breeders to use of breeding records to reduce Complex Vertebral Malformation, a genetically transmitted defect that causes abortions and stillborn calves.
Approximately 15 percent of Select Sires’ current sire lineup carries the condition, according to Chuck Sattler, Select’s vice president of dairy progeny testing. No specific numbers of affected bulls or cows are available, but Sattler estimates that most A.I. companies are equally affected nationwide.
Indications. The condition is a recessively inherited genetic defect discovered last year by Danish scientists. The gene that causes the defect was identified in August. Several cases have been identified and confirmed in the United States.
The defect, present in the Holstein breed for many generations, is suspected to cause embryonic deaths, abortions and stillborn calves, according to Kent Weigel, genetic specialist at the University of Wisconsin.
Based on research to date, the defect results in abortion in 66 percent of cases and stillborn calves in 33 percent of cases.
Abortions related to the defect may happen at any time. Stillborn calves are typically delivered from 250 to 283 days gestation, and the most noticeable defects are malformed legs with rigid pasterns. A shortened neck may also be visible.
Examinations of calves with the condition also show curvature of the spine, fused vertebrae and fused or missing ribs, according to Weigel.
Approximately half of the affected calves also exhibit cardiac abnormalities, according to David Steffen, DVM and pathologist at the University of Nebraska at Lincoln.
Post-mortem exams are needed to continue research on the defect, as well as to differentiate calves affected by CVM with those with defects caused by environmental factors, Steffen said.
Widespread. Data has identified U.S. sire 7H543 Carlin-M Ivanhoe Bell, a popular sire in the United States, as a common ancestor maternally and paternally in the pedigree of all affected calves.
“The Bell sire is the first one we’ve recognized, but we’re still looking for the source,” said Sattler.
The defect is carried on the recessive gene, so several carriers are expected to be found, he said. An animal can have one copy of the mutated gene, but only when mated with another carrier is there the chance to see the defect.
“This isn’t to the degree of an epidemic, but as far as lethal genetic defects go, this one has become fairly prevalent,” Sattler said.
“On an individual farm basis, it’s not too bad,” with roughly one CVM-affected calf born each year in a herd of 200 cows, “but it’s a significant loss when analyzed with national herd numbers,” he said.
Ongoing tests. Danish researchers are conducting tests to identify whether an animal has the gene that can cause CVM. The laboratory began processing samples commercially in September 2001.
Of Select Sires’ bulls tested, 10 of 90 are listed as carriers on the company’s Web site. Tissue samples have been collected from all Select Sires bulls and are awaiting testing.
ABS Global has tested 650 bulls, including their current lineup. Of those, 120 are carriers. The company continues to test bulls in waiting and those without proofs, according to Denny Funk, chief genetics officer.
The Alta Genetics site lists one of 27 bulls as a carrier, and Accelerated Genetics lists six of 46 as carriers.
The issue’s impact is expected to decrease dramatically in the next five years, as affected bulls are eliminated or breeding programs are coordinated to reduce mating of gene-carrying sires and dams. It’s also expected that A.I. companies will avoid buying bulls that carry the gene.
“Breeders can continue to use tested carrier bulls without worrying too much. This is one of those things that can be managed and worked around,” Sattler said.
Dairy farmers who do not use A.I. are at a greater risk for spreading the defect within their herds, Sattler said, because of the risk of untested bulls carrying the defective gene.
The National Association of Animal Breeders and Holstein USA are aggressively collecting data on this condition and are currently arranging research aimed at studying the inheritance and genotypic markers in affected calves and their parents.
Select Sires has sent tissue samples from nearly 500 bulls, including those currently marketed heavily. The company has also sent samples on older bulls in order to update breeder directories and mating programs to check the CVM status of a cow’s sire and maternal grandsire.
Producers are encouraged to report suspected calves to Holstein Association USA or A.I. representatives.
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CVM: What you can do
The following is a checklist for managing your dairy herd to decrease the risk of CVM.
* Set up a system for accurate recording of sire and maternal grandsire identification for all cows in your herd, if you haven’t done so already.
* Make a list or spreadsheet file that shows the CVM status of the sire and maternal grandsire of each cow in your herd.
* Use a selection index to identify the group of A.I. sires you’d like to use in your herd during the next three months.
* Check to see which of these bulls are CVM carriers, and avoid using these bulls on any cows whose sire or maternal grandsire is a carrier.
Source: Kent Weigel, genetic specialist at the University of Wisconsin and genetic programs administrator, National Association of Animal Breeders
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Frequently asked questions
How much could CVM impact my herd?
Although the percentage of cows that are CVM carriers has not yet been 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.
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 Holstein bulls carried BLAD 10 years ago and very few carrier bulls are available today.
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 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.
Source: Kent Weigel, genetic specialist at the University of Wisconsin and genetic programs administrator, National Association of Animal Breeders
(You can contact Andrea Myers at 1-800-837-3419, ext. 22, or by e-mail at amyers@farmanddairy.com.)
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