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Post by Cascade Meadows Farm - Kirk on Nov 28, 2012 16:23:30 GMT -5
Gene is correct. If these genetic issues start showing up in Dexters then that indicates someone hasn't been truthful and registered crossbred animals. This is 100% false. Genetics 101 will tell you that genes mutate every day. The diseased genes are simply miscopied genes. A major source of mutations is sperm production. Bulls produce 5 billion sperm each day. Copying errors occur in thousands of sperm EVERY day in EVERY bull. It's just a matter of chance as to whether a sperm carrying a defective gene reaches the egg first. Since bulls produce 5 billion sperm per day, the number of non-mutated sperm greatly outnumbers the mutated sperm. So the number of freshly mutated calves is quite low. A legacy calf named Wheat-ear, is thought to be one of these fresh mutations and her sire's miscopied sperm is likely the starting point of the PHA defect. Interesting to note that Wheat-ear comes from a CLOSED herd of legacy dexters. Once the mutation occurs and carrier calf like Wheatear is created, the mutated gene can hide and be spread and passed down to future generations. That's Genetics 101 |
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Post by kansasdexters on Nov 28, 2012 16:43:20 GMT -5
I'm going to add the following information for reference purposes:
Yes, there are two forms of Chondrodysplasia that have been identified in Dexter cattle, that is a true statement. However, one form of Chondrodysplasia is found only in the descendents of Meadowpark Charles, the first (up-graded) purebred Dexter bull born in New Zealand. It is not found in Dexter cattle in the United States or Canada or England or Ireland.
Here is how New Zealand got it's own unique Chondrodysplasia mutation:
Alec and Anne Meades led the introduction of Dexter cattle into New Zealand. Their Meadowpark herd was the first Dexter herd in New Zealand to breed significant numbers of pure-bred Dexter cattle. They collected semen (1 bull) and embryos to expand the number of pure-bred Dexter cattle available at the time (in the late 1980's and in the 1990's) in New Zealand. Then, another breeder (in New Zealand) founded his herd on Meadowpark cattle and multiplied those bloodline even further through extensive embryo and semen collection efforts. The only other source of pure-bred Dexter in those early days in New Zealand was through imported semen.
Alec and Ann Meades had chosen Red Poll/Jersey cross-bred females as the foundation females for their upgrade breeding program. No bulldog calves were born at Meadowpark, so they had no warning of any potential problem. Since both sire and dam must be carriers of the mutated gene, and both must pass the mutated gene onto the calf, in order for the calf to be a non-viable "bulldog" calf, it just doesn't happen very often (the statistical probability of that happening is only 25%). If only one parent passes on the mutated gene, the calf is a carrier and becomes a dwarf (aka "shortlegged") -- which, for many Dexter breeders is a desirable result.
Since Meadowpark was the primary source of Dexter cattle throughout New Zealand, it was only a matter of time until males and females (with Meadowpark-based pedigrees) were bred to each other and some bulldog calves were produced. This happened before there was any genetic test for Chondrodysplasia (either form of Chondro). Nancy Edge wrote an article that was published in December 2003 (The International Dexter, Issue No. 3) and she states, "the number of bulldog calves is very small. To date, only 14 bulldog calves have been recorded out of over 2,068 animals registered with the Society -- less than 1%."
New Zealanders now have a genetic test for their unique Chondrodysplasia gene, in addition to the test for the original Chondrodysplasia gene that is available worldwide and has been since 2003.
The Dexter PHA mutation came to the United States and Canada with the importation of a PHA-carrier cow, Woodmagic Wheatear. We don't know if she inherited this mutation from her sire or from her dam. We don't know how far back it goes. Neither her sire, nor her dam were tested for PHA. To date, the Dexter Cattle Society in the U.K. has not published any testing results for PHA in the Dexter cattle of their country, that I'm aware of.
But the story of PHA in North America is very similar to what happened in New Zealand. Woodmagic Wheatear was an excellent Dexter cow, her son (Aldebaran Priapus) was the first Dexter bull collected for AI in Canada. Woodmagic Wheatear was flushed for embryos and those embryos were exported to Australia, as was semen from her grandson (Trillium Chabotte), another PHA-carrier. Several sons of Aldebaran Priapus were imported into the United States and used extensively by major breeders. That's why Woodmagic Wheatear has so many descendants in the ADCA registry and that's why we now test for PHA. We've only had the ability to test for PHA since 2009. Woodmagic Wheatear was imported into Canada in 1978. Her son, Aldebaran Priapus, was born in Canada in 1982. Aldebaran Priapus' son, Trillium Chabotte, was born in Canada in 1985.
From those recent past experiences, we know that a recessive genetic mutation can be a hidden problem that spreads unseen through many Dexter herds over many years. Those past experiences also caution us against the widespread and unchecked use of only a few AI bulls. It may become very worthwhile to require additional genetic testing and/or progeny testing on "out of herd" Dexter AI bulls in the near future.
Patti
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Post by dexterfarm on Nov 28, 2012 16:51:21 GMT -5
Gene is right those dna mutations would not enter the dexter breed if not already there unless it was out crossed. If there were to be a new mutation it would not be the same. It is possible there could be a mutation that had similar results but would not be the same and the current test would not work. Just like PHA the PHA in other breeds is not the same and the test for dexter pha does not detect the other ones.
As far as the PHA mutation starting with Wheatear we just dont know because we cant trace it back any further than that. It is possible it was in the woodmagic heard from the start. I am not saying that it was in there from the start but it is possible. Look how long it took to surface here.
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Post by Olga on Nov 28, 2012 17:01:28 GMT -5
Here is my opinion on "Genetic Elimination Policy":
I think it would be a good idea if a standard form for reporting an abnormal calf was selected or compiled by the ADCA leadership. Such form should be printed in every bulletin and also should be available on the ADCA website. This would allow owners who are presented with any type of abnormality in a newborn calf to report such an issue. Such protocol exists in many other breed organizations.
For all I know, ADCA might already have such a form. But if they do, it is not easily accessible.
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Post by rezzfullacres on Nov 28, 2012 17:09:56 GMT -5
This is a little off subject BUT I think it will make a point. I have a brood cow and her mother. Mother has been dehorned but her horns were normal appearing before that. Said cow has one "normal horn" and one crooked horn...I thought the horn had been damaged when young, I was wrong...This cow has had 2 calves, both have 1 normal horn and 1 crooked horn, it aims more straight sideways than a gentle forward sweep. Now these calves are from 1 bull, with normal horns, she is bred to another so we shall see BUT to me it seems that this is a genetic defect that was not present in either parent, something went haywire in the genetics to cause this crooked horn and now it is being passed on.....
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Post by Cascade Meadows Farm - Kirk on Nov 28, 2012 17:42:08 GMT -5
Those past experiences also caution us against the widespread and unchecked use of only a few AI bulls. It may become very worthwhile to require additional genetic testing and/or progeny testing on "out of herd" Dexter AI bulls in the near future Thanks to Patti for sharing her amazing bank of knowledge!!! But I just want to comment on the last statement. While I think it's a good idea to have a nicely diversified catalog of AI bulls (to help maintain genetic diversity), the MAJOR problem in spreading genetic disease is the LACK OF PROGENY TESTING in ALL AI bulls (regardless of their source). "In-herd" bulls are just as much at risk of carrying a genetic disease mutation as "Out-of-Herd" bulls. Hair Sample DNA testing for known diseases like PHA and Chondrodysplasia is a given. But as discussed earlier, the BEST way to test for new unknown diseases is to breed a potential AI bull on his own daughters (as well as his own mother and his sisters) first, before listing him for general use. If this had been done with Wheatear/Aldebaran Priapus, the problem could have been found and eliminated before it spread via widespread AI Every bull in the AI catalog should be considered risky and experimental until a progeny test is conducted. I'd hope that the associations phase in some progeny testing rules for ALL AI bulls. By the way, the new AI bull named Microcosm has over 20 daughters of breeding age. It would be a simple matter for the owners to breed him back on 10-20 daughters for a progeny test. He could easily become the first AI bull progeny-tested free from ALL known and unknown genetic disease with 99.9% certainty. AI or not, testing a bull on his own mother and sisters and daughters can be a good idea to help look for any undiscovered genetic problems, and if you find a problem REPORT IT along with photos and DNA samples. |
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Post by Cascade Meadows Farm - Kirk on Nov 28, 2012 18:11:37 GMT -5
Gene is right those dna mutations would not enter the dexter breed if not already there unless it was out crossed. If there were to be a new mutation it would not be the same. It is possible there could be a mutation that had similar results but would not be the same and the current test would not work. Just like PHA the PHA in other breeds is not the same and the test for dexter pha does not detect the other ones. As far as the PHA mutation starting with Wheatear we just dont know because we cant trace it back any further than that. It is possible it was in the woodmagic heard from the start. I am not saying that it was in there from the start but it is possible. Look how long it took to surface here. Genetic diseases are typically the result of broken genes while the good version of the gene codes for an important biological function. So, yes, you can break those genes in various ways and get the same disease effect. I think we're agreeing that those diseases (found by the Angus folks) may ALL be found in dexters someday, but yes, the broken genes may look different (likely) or they could be identical (less likely). But every disease on the Angus list could be found in Dexters WITHOUT an introgression. Concerning Wheatear, if PHA had been in the Woodmagic herd from the start, Beryl's extensive closed-herd inbreeding would likely have encountered it over and over and over with dead calves. Recessives are easily found via inbreeding. |
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Post by Cascade Meadows Farm - Kirk on Nov 28, 2012 22:20:33 GMT -5
Two genetic defects that occasionally occur in most all cattle, pigs, and sheep (and other mammals) from time to time are Hypotrichosis and Syndactyly (both on the lists of genetic diseases provided earlier). Hypotrichosis is hairlessness. It's a simple recessive gene that interferes with normal hair production. It occurs regularly in cattle. I couldn't find a good photo in cattle, but here's what it looks like in cats (you can imagine what a cow would look like).  Syndactyly is mule-footedness. The recessive defect gene causes the hooves to fuse together   When we find these hidden defect genes in dexters, will the dexter associations allow breeders to combine chondrodysplasia with syndactyly and hypotrichosis to create hairless, mule-footed, dwarfs? (oh, they are soooo cute and 100% pure dexter too!, maybe even legacy!). Or will the dexter associations take a stand against promoting the spread of genetic diseases that other cattle breed associations are trying to eliminate? Maybe the first baby-step is to REQUIRE the suspected carriers of ALL genetic diseases to be tested and if they are carriers, to be LISTED in the registry as carriers. That's what other breed associations are doing to keep members from hiding the carriers. |
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Post by littlecowfl on Nov 29, 2012 5:27:43 GMT -5
Kirk, I appreciate your enthusiasm, but most of us are small producers and do not wish to breed our heifer calves back to the bull because we sell the heifers at weaning age, rather than as bred heifers. A bigger operation could possibly do this and sell the offspring as freezer beef (people generally don't want inbred cattle). I have a promising young bull to offer as an AI bull. I bought after carefully researching bloodlines and breeders (he is PHA and Chondro free). I would lose a lot of money in feeding, pregnancy and calf costs if I spent time breeding him to his daughters and his mother first.
The good news is that his original breeder will be purchasing many of his straws and there will be some informal testing done when those straws are used with cows that are closely related to him. I know his breeder is also a very conscientious person and will alert me if there are any problems.
Furthermore, despite our best efforts, unexpected inbred calves do occasionally occur, especially when you keep one bull for many years, which we plan to do with ours, and you bet I would do the right thing if there was something wrong with one of his calves.
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Post by lakeportfarms on Nov 29, 2012 5:57:35 GMT -5
That is a silly statement, and an insult to the good and responsible breeders of some very fine Dexters.
From the ADCA site for breed standards:
These standards existed before most, if not all of us became owners of the breed. I don't see where it mentions hairless, or mule-footedness in the breed standard.
Chondrodysplasia is a characteristic of Dexters, like it or not, and has been for years. PHA has been a more recent mutation, and steps are taken by responsible breeders to allow for the continued use and registration of these bloodlines in an appropriate way. I'm fine with that, and all of our herd has been tested for PHA and the results posted so we're doing our part as well.
If other genetic issues crop up, responsible breeders will report them and a determination will be made as to the threat to the breed. PHA is your example for that, with a lot of work by several people to isolate and develop a test to help control it and allow others to avoid it.
There are trade offs with any breed of cattle out there. Don't like the chondro genetics? Why not sell your Dexter herd and switch over to Angus or lowlines that you feel is more proactive with genetic issues. Oh, you don't like the temperament of those breeds? Thn live with the chondrodysplasia and to a lesser extent PHA in Dexters. Clearly you have the ability to avoid it in your own herd. Some of us choose not to.
And i agree with Gene, quit scaremongering. If there is anybody considering Dexters who has stumbled on this site and doing their research, they've possibly moved on and decided on a Jersey or some other breed that might better fit their needs. And with all this rancor and intolerance you won't have potentially sold any of your chondro/PHA free Dexters either, instead of just convincing them about how bad your competition is by breeding chondro or PHA carriers when they'd be better off butchered or relegated to the "black market" of unregistered Dexters.
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Post by Tanya on Nov 29, 2012 7:31:38 GMT -5
Knock it off with the fear mongering. When someone wants to shut someone else down, or doesn't want to hear what the other has to say, they call it "fear mongering." Bullocks! Future Dexter breeders do not need to be sheltered from the conversations that will help them decide for THEMSELVES what is the LOGICAL to them. I believe they have brains in their head or they wouldn't be raising, or contemplating raising, such incredible creatures as our beloved Dexters in the first place. Much of what Kirk is saying makes PERFECT sense to me and many others who are taking the time to comment and still others who I know personally agree with his approach, but do not frequently post on this board. Ive noticed Kirk is keeping it respectful. Lets all try and do the same and remember we all have a RIGHT to our opinions. You wouldn't want to be SHUT down for your opinion. So do not attempt to shut down another, just because you do not agree with their post. Thanks!
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Post by lakeportfarms on Nov 29, 2012 8:39:57 GMT -5
You call that respectful?
Where have you seen a post of mine whereby I stick my head in the sand and deny that chondro or PHA exists, or that other genetic issues may rear their head one day that may need to be addressed, or that a chondro Dexter is the only Dexter that should be allowed into the registry, or shows?
Breed standards exist for a reason, and that is to define the expectations for owners in their decision toward a breed to raise, or animals that will make up a herd. Breed standards are developed to provide certainty and continuity to people who make significant investments in both time and money toward their herd.
The breed standards for ADCA Dexters are specified (and published) so that the whim of one (or 100) owners who don't happen to like the look of, or steps required to breed carriers to non-carriers to avoid bulldog, or PHA affected calves can invalidate the breeding decisions of hundreds of owners who have in good faith relied upon the integrity of the association to follow their own published standards. If an association doesn't have the integrity to do that, how can you expect individual breeders to show any integrity?
Unlike Kirk and some others, I'm not advocating the rejection of animals from the registry that are larger (or smaller) than the breed standard, for example, which is tantamount to the same thing they are proposing. This argument about chondrodysplasia in particular is foolish and a waste of time, because the consequences of banning all future registrations of carrier calves is akin to cutting of your nose to spite your face for the ADCA, or as Gene pointed out in an earlier post, PDCA.
I have expanded our herd of Dexters (including chondro carriers) with the expectation that the rules would not be changed in the middle of the game. "Short legged" Dexters have equal merit with "long legged" Dexters in accordance with the breed standard, I suspect long before any of us were even aware of the breed, and will always have their following. Period, end of story. Live with it.
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Post by midhilldexters on Nov 29, 2012 8:40:14 GMT -5
Elemental, I agree. The more things are discussed in the open the better for the breed. Breeder responsibility is paramount, if breeders can access information easily then they have no excuse.
Kirk, I think you have way more support than you know.
Carol K
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Post by Olga on Nov 29, 2012 9:27:24 GMT -5
To sum this issue up already...
It is not that Kirk is wrong in expressing his ideas, is that he is becoming redundant and he is trying to ridicule those who don't agree with him. That is not how debates are won.
On the issue of "genetic defects", the very definition of which is a subject of lengthy controversy, Kirk is a radical. He is the first one who has ever openly, to my knowledge, proposed a quick and decisive amputation of all "defective" Dexters from the registry.
To this I say: “If you don't like something, change it. If you can't change it, change your attitude. Don't complain.” (Maya Angelou)
There is a process by which Kirk could write a proposal for a change to the ADCA registration procedures, he could amass supporters, he could run for office in ADCA, etc. He could write an article into the bulletin to reach out to Dexter Proboards non-user audience.
As to here, I think we got Kirk's point.
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Post by Cascade Meadows Farm - Kirk on Nov 29, 2012 11:20:26 GMT -5
he is trying to ridicule those who don't agree with him.... Kirk is a radical. He is the first one who has ever openly, to my knowledge, proposed a quick and decisive amputation of all "defective" Dexters from the registry.. Wrong summation, but let me help. 1. I'm not ridiculing anyone. I'm honestly asking how we will deal with future found defective genes. We will find all sorts of interesting defects in the future and some breeders might choose to capitalize on them. The hairless defect has been capitalized on by many breeders in other species (the pictured cat above is a show winner). The mulefoot defect has an entire pig breed based on it (mulefoot hogs). Our standards say nothing about disallowing defects. Will we allow them, or not? Will we (all dexter registries) work on a policy that addresses defects or not? 2. I am NOT proposing a "Quick and decisive amputation of Defective Dexters" I am ABSOLUTELY OPPOSED TO THAT. If you reread all my posts above, you will see that I proposed KEEPING ALL CURRENT defective animals in the registries FOREVER. I even proposed allowing defective new calves to be registered until 2018. That means that a defective calf born in 2017 could be registered and bred from from until 2040 (Where's the quick and decisive amputation in that?) 3. I'm NOT the first to propose anything. This has been proposed and discussed many times in the past decade (Gene, even said this above). In fact, my very slow proposition, is SLOWER than past proposals. 4. I hardly think I'm being radical. I'm suggesting that we SLOWLY work towards implementing a similar defect policy to that of the LARGEST registries on earth. Nothing radical about SLOWLY copying what the majority associations have already been doing. 5. I didn't think this board was an ADCA forum, but rather a forum for ALL dexter breeders world-wide. I'm making this proposal to a WORLD-WIDE audience. I'm proposing that ALL dexter registries consider the issue of genetic defects before we spread more defects far and wide by our inaction. I know of no better international forum than this, for this discussion. Now all that said.... I appreciate this board very much and I appreciate the moderator VERY VERY much for facilitating this fine forum. PS. Many years ago I did take a strong role in helping the ADCA implement carrier tracking on the pedigrees and the online pedigree system. I'm VERY disappointed to see that MOST chondrodysplasia-affected animals are still NOT coded in the system. Are there really only 300 chondro-carriers in the ADCA? |
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