Arthrogryposis Multiplex – Information for Cow-Calf Producers
Livestock Update, March 2009
Scott P. Greiner, Ph.D., Extension Animal Scientist, VA Tech
Last fall, the American Angus Association announced the presence of a genetic defect in Angus cattle called Arthrogryposis Multiplex (AM; aka Curly Calf Syndrome). Research has confirmed that AM is a lethal genetic defect which is inherited as a simple recessive. As a simple recessive, the condition is controlled by a single pair of genes. For a calf to be affected, it must inherit the AM gene from both of its parents. AM calves are dead at birth with a bent or twisted spine, are small and thin muscled, and their legs are often rigid and hyper-extended.
The chances of having an AM calf are directly related to the probability of herd sires and cows being carriers of the AM gene. Carrier animals possess the AM gene, and although they are not affected themselves, they will pass the effective gene to their progeny 50% of the time. When a carrier bull is mated to a carrier cow, on average 25% of the calves will have the AM condition and 75% of the calves will be normal. However, some of these normal appearing calves will be carriers of the AM gene (one copy of the AM gene, inherited either from their sire or dam) and have the ability to pass the gene on to their progeny. As a simple recessive, AM is inherited in a very similar fashion to coat color (black vs. red) and horns in beef cattle- both simple recessives which many producers are familiar with. Since AM results only when a calf inherits the AM gene from both of its parents, if one parent is free of the AM gene, it is not possible to have an affected calf.
The American Angus Association has published an extensive list of animals which have been DNA tested for the absence (AMF- Arthrogryposis Multiplex Free) or presence (AMC- Arthrogryposis Multiplex Carrier) of the AM gene. This comprehensive list provides the AM genotype for the majority of Angus sires utilized AI. Commercial cow-calf producers can do a simple risk assessment for their herd by utilizing this published list. For example, assume a herd has a natural service son of a known carrier (AMC) bull. This son of a known carrier bulls has a 50% chance of being a carrier himself. Taken one step further, if daughters of this bull (son of known AM carrier) were retained in the herd, they have a 25% chance of being carriers (grandprogeny of known carriers have 25% of being carriers themselves). Using this approach, producers can get a feel for the potential frequency of the AM gene in their cowherds based on the ancestry of recent sires used in the herd. Herds which have used known carrier bulls AI, or sons of known carrier bulls, have a higher probability of carrier females within the cow herd.
As stated earlier, both the sire and dam must be carriers to result in an AM calf. Consequently, if only AMF sires are used in a herd, the AM condition will not manifest itself. The use of AMF bulls certainly is the quickest and surest way to eliminate the risk of having an AM calf. Through DNA genotyping, current herdsires can be tested to determine if they are AMF or AMC. For bulls with carrier animals in their ancestry, DNA testing may be warranted, particularly in herds which have potential carrier females. The DNA test can be performed using a hair root or blood sample, and costs approximately $25 per animal. Definitive knowledge of the AM genotype of sires will allow for prudent mating decisions. Additionally, knowing the genotype of a bull allows for more accurate prediction as to the status of his progeny.
Moving forward, the application of DNA genotyping will present bull buyers with the ability to make informed decisions regarding AM status, as most seedstock suppliers will test bulls prior to offering them for sale. Additionally, seedstock producers are well versed in the pedigree lineage of the bulls they have sold their customers in previous years, and can assist cow-calf producers in identifying bulls currently in use which are candidates to be DNA tested (ie. if current herdsire is at risk of being carrier based on ancestral information). Assessing the risk of an animal can become complex, as the pedigree needs to be evaluated several generations back (on both sire and dam side) to identify if an animal is a potential carrier. Seedstock producers are in the best position to assist commercial cattlemen in accomplishing this task.
While the focus of AM has logically been with registered Angus cattle, the principles of inheritance of this condition extend to other breeds and crosses which are Angus-influenced. As an example, Gelbvieh Balancer and SimAngus genetics in commercial herds also need to be evaluated as to their AM status due to their Angus ancestry.
In summary, AM is likely not to be a significant problem in most commercial cow calf operations. The risk will vary from herd to herd based on the genetics which have been utilized. While DNA testing is the only way to predict with certainty if an animal is a carrier or not, risk assessment based on pedigree information and testing of current herd sires (if warranted based on pedigree risk) provide a practical means for commercial producers to address this issue.
Additional information on AM, including a list of known carrier sires and details on testing procedures and laboratories can be found on the American Angus Association web site www.angus.org.
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