In 2008 and 2009 Aberdeen Angus cattle breeders had to come to terms with the presence of two genetic defects in some of our cattle. This page is my personal attempt to explain the defects and their effect in simple terms, while exploring some of the implications as I proceed.
Arthrogryposis Multiplex (AM), also sometimes referred to in the US as Curly Calf Syndrome (CCS), is a recessive lethal genetic defect. Being recessive, an animal may carry the defect without any physical sign, because it will also have a (dominant) good copy of the gene. But when two carriers are mated together there is a 25% chance of both parents contributing the defective gene to the calf, leading to its malformation and death, generally before birth. Half of the offspring of such matings would be carriers which appear normal and one quarter would be free of the defect and therefore never able to pass it on to their own calves.
The earliest tested carrier of the defect was US-bred Rito 9J9 OF B156 7T26. If that bull appears in the pedigree of any of your animals, and the descent from him to your animal is not broken by a tested Arthrogryposis Multiplex Free (AMF) animal, your animal is a potential carrier of the defect.
The NZ Angus Association eventually provided, and then removed, information on its website about AM and its response to the defect.
Most potential NZ Angus carriers are now tested and their test results are available on the NZ Angus database. Registered breeders continued for some time offering tested carrier bulls for sale, without drawing buyers' notice to that fact in their catalogues. Buyer, beware!
If an animal has come from US stock and has "pedigree unavailable" on the NZ database, its details may be found in the American Angus Association pedigree database.
Let us say you are looking to buy a bull. Upon receipt of a printed sale catalogue you find bull "A" fits your requirements but there is no indication of his status with regard to either AM or NH.
Looking at his pedigree record in the NZ Angus database, you discover his sire, "B", has been tested AMF, which breaks the chain of possible inheritance of the defect from bull "J" which was tested as a carrier.
However, on his dam's side, while bull "F" has been tested AMF, which reassures you in regard to cow M's possible carrier status, you find that your bull's great-grand dam, cow "O", was sired by a bull which has tested AMC and there is no test result for any of the animals in the descent between that bull and yours.
You then contact the breeder and ask if they've had the sale bull tested?
They tell you they have not, because they tested their breeding cows and cow "C" has tested AMF. Thus the bull you wish to buy will be AMF.
Neuropathic Hydrocephalus (NH) is a recessive lethal genetic defect. Being recessive, an animal may carry the defect without any physical sign, but when two carriers are mated together there is a 25% chance of both parents contributing the defective gene to the calf, leading to its malformation and death before birth. Half of the offspring of such matings would be carriers which appear normal and one quarter would be free of the condition and therefore never able to pass it on to their own calves. It appears to have originated in the US Bull GAR Precision 1680 (both of his parents test clear of the defect), born in 1980. He, and his widely-used son, C A Future Direction are both carriers of AM and NH.
Animals with the above-mentioned bulls in their pedigrees may carry both defects, either, or none. AM and NH are inherited independently, so an AMF result tells you nothing about the NH status of an animal. Modern testing usually offers the tests for AM and NH together, at a cheaper rate than was originally the case.
Let us go back to your sale catalogue.
Bull "J" is now known not only to be a carrier of AM, but also of NH. Bull "B" is a well-known AI sire and has been tested as NHC, a carrier of Neuropathic Hydrocephalus. There is no mention of either AM or NH in the sale catalogue and bull "B" is the sire of several of the bulls for sale.
In the catalogue there are the usual provisions around guarantees of fertility, but no assurance that bulls which are subsequently proven to be carriers of either of these known genetic disorders, will be subject to any similar guarantee in regard to replacement or refund.
What will you do?
What will the breeder do about testing the bull you buy?
What comeback will you have if your bull tests as a carrier?
The New Zealand Angus breeders' approach to these defects was very disappointing and led to my own resignation from the Angus Association because the Association refused to take a stand and prevent the further spread of the genes into the commercial cattle population. There is no doubt still a significant number of carrier cattle in the wider Angus-based cattle herd.
Responsible seed-stock breeders will eliminate carriers of genetic defects from their herds, or, if they choose to keep some carriers because of their superiority in other respects, they will test all off-spring and only sell those which are tested free of the defects.
By ceasing to sell carrier bulls into the commercial population, the frequency of carrier cattle will gradually decrease, although recessive genes can reside in the population for generations if no testing is done to expose them.
If as a commercial breeder using Angus cattle you suspect or know you have bought stock of the affected family lines, you may have carriers in your own herd. To avoid the possibility of producing affected calves, you must therefore ensure you always use tested defect-free bulls over your cows and heifers, or bulls from unaffected family lines. If you have a particular desire to ensure there are no carriers in your herd, testing is a simple matter of submitting a tail-hair sample to a laboratory which is licensed to perform the appropriate test/s. Collecting a sample involves pulling about thirty tail hairs from your animal, so the roots of the hairs are pulled out, and putting them into a clean envelope. A combined test currently costs $49 (+ GST, Zoetis) per animal.
Does this mean Angus are bad cattle? No. Genetic defects are present in all populations. There are known defects in all the mainstream cattle breeds in this country. The advantage of knowing about the defects is our ability to avoid them or to breed around them. So, ask any breeder from whom you wish to buy cattle what genetic defects are known in his or her breed and specifically ask if they have been tested for in the animals you are interested in purchasing. Not all cattle require testing, because not all defects are present in all family lines, but your breeder should be aware of the possibilities in their breed and willing to discuss them openly.
Please feel free to contact me with comments or questions about this page or the information it contains.
Ruth Renner, June 2009 (updated April 2012, June 2015, August 2019).