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Line-breeding and in-breeding thoughts & reasons

This is a discussion on Line-breeding and in-breeding thoughts & reasons within the Horse Breeding forums, part of the Horse Breeds, Breeding, and Genetics category

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        09-20-2013, 09:58 AM
      #31
    Green Broke
    Quote:
    Originally Posted by Foxhunter    
    I find this all very interesting. I do know that with father to daughter or mother to son breeding the first generation are usually fine but, it is the offspring from the second generation that often goes wrong.

    Getting away from horses, there is a family locally that married 'close' first cousin to first cousin twice. The result from the one part of the family I knew would prove that line breeding in humans was not a good thing!
    Two sons were certifiable with mental disorders and one of the two daughters exceedingly 'slow' with learning disabilities.
    Humans don't stringently "cull" so therein lies the problem. The odds that people aren't bright enough to know not to breed with their close kin would certainly support inbreeding daftness..LOL
    The odds that educated, superiorly intelligent kin with no genetic defects would inbreed is pretty slim I think..
         
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        09-20-2013, 10:31 AM
      #32
    Trained
    In-breeding and line-breeding DOES NOT IN ANY WAY, SHAPE OR FORM CAUSE DEFECTS IN THE OFFSPRING! Genetic defects that are ALREADY IN THE GENE POOL may become more apparent, but the defects are not caused by the manner of crossing.

    Say a mare has a recessive gene for "bunkylegitis". Now, she has the recessive form, and only one copy. So she has perfectly fine legs. She is bred to a stallion who has no copy of bunkylegitis, so she has a 50% chance of passing down this gene to her offspring - who, incidently, won't express it as it is recessive. So let's continue the theoretical - say she has two colts, one of whom inherits bunkylegitis, and one that doesn't. Remember, they are not expressing it, but one of them has the recessive gene for it. Now, let's say we bred both of them back to their dam. Colt A has no copy of the recessive gene, so there is a 50% chance that the offspring get the gene from their dam, but, as it is recessive, it isn't going to impact them at all. Colt B has received a copy of the gene, but has no effects as he only has one copy of it. However, when bred to his dam, their offspring has a 25% chance to inherit two copies of the bunkylegitis gene, and when you have two copies of a recessive gene, it expresses. All of a sudden, we have a foal with legs so wonky it can't walk straight, fails sobriety tests its whole life, and generally looks bad for the family line. This isn't caused by the in-breeding - it is highlighted by it.

    The point I am making is that a responsible breeder would do many things with this situation. First of all, if there was any known cases of bunkylegitis in the horse's pedigree, a responsible breeder would select outcrosses very carefully in order to ensure no second copy of bunkylegitis was introduced. They would test their breeding stock stringently, and not breed two horses that both carry a copy of the bunkylegitis gene. And, should it come up by surprise, they would humanely deal with the resulting foal (whether that is culling or gelding/spaying would depend on the severity) AND never make that particular cross again.

    In-breeding does not cause problems. Irresponsible breeders that don't do their research or operate with integrity do.
         
        09-20-2013, 10:38 AM
      #33
    Yearling
    Quote:
    Originally Posted by Druydess    
    Humans don't stringently "cull" so therein lies the problem. The odds that people aren't bright enough to know not to breed with their close kin would certainly support inbreeding daftness..LOL
    The odds that educated, superiorly intelligent kin with no genetic defects would inbreed is pretty slim I think..

    I'm confused now, are you for in-breeding, or against it? With the above statement, you are stating that it's not a good thing and essentially shouldn't be done. That educated, intelligent individuals wouldn't in-breed.

    Yet earlier, you stated that it should be done to produce the traits you desire in an off-spring. Could you please clarify?
         
        09-20-2013, 10:43 AM
      #34
    Green Broke
    Quote:
    Originally Posted by busysmurf    
    I'm confused now, are you for in-breeding, or against it? With the above statement, you are stating that it's not a good thing and essentially shouldn't be done. That educated, intelligent individuals wouldn't in-breed.

    Yet earlier, you stated that it should be done to produce the traits you desire in an off-spring. Could you please clarify?
    I think you missed the entire point about stringent culling. If you line-breed or inbreed with individuals are appropriate for it, then it is successful. If you use Billy-Bob and Bobby Sue, who already are poor representations, then you get what you put into the equation.
         
        09-20-2013, 10:46 AM
      #35
    Green Broke
    Quote:
    Originally Posted by Chiilaa    
    In-breeding and line-breeding DOES NOT IN ANY WAY, SHAPE OR FORM CAUSE DEFECTS IN THE OFFSPRING! Genetic defects that are ALREADY IN THE GENE POOL may become more apparent, but the defects are not caused by the manner of crossing.

    In-breeding does not cause problems. Irresponsible breeders that don't do their research or operate with integrity do.
    Thank you Chiilaa!! This is exactly right!!
         
        09-20-2013, 11:10 AM
      #36
    Yearling
    Quote:
    Originally Posted by Chiilaa    
    In-breeding and line-breeding DOES NOT IN ANY WAY, SHAPE OR FORM CAUSE DEFECTS IN THE OFFSPRING! Genetic defects that are ALREADY IN THE GENE POOL may become more apparent, but the defects are not caused by the manner of crossing.

    Say a mare has a recessive gene for "bunkylegitis". Now, she has the recessive form, and only one copy. So she has perfectly fine legs. She is bred to a stallion who has no copy of bunkylegitis, so she has a 50% chance of passing down this gene to her offspring - who, incidently, won't express it as it is recessive. So let's continue the theoretical - say she has two colts, one of whom inherits bunkylegitis, and one that doesn't. Remember, they are not expressing it, but one of them has the recessive gene for it. Now, let's say we bred both of them back to their dam. Colt A has no copy of the recessive gene, so there is a 50% chance that the offspring get the gene from their dam, but, as it is recessive, it isn't going to impact them at all. Colt B has received a copy of the gene, but has no effects as he only has one copy of it. However, when bred to his dam, their offspring has a 25% chance to inherit two copies of the bunkylegitis gene, and when you have two copies of a recessive gene, it expresses. All of a sudden, we have a foal with legs so wonky it can't walk straight, fails sobriety tests its whole life, and generally looks bad for the family line. This isn't caused by the in-breeding - it is highlighted by it.

    The point I am making is that a responsible breeder would do many things with this situation. First of all, if there was any known cases of bunkylegitis in the horse's pedigree, a responsible breeder would select outcrosses very carefully in order to ensure no second copy of bunkylegitis was introduced. They would test their breeding stock stringently, and not breed two horses that both carry a copy of the bunkylegitis gene. And, should it come up by surprise, they would humanely deal with the resulting foal (whether that is culling or gelding/spaying would depend on the severity) AND never make that particular cross again.

    In-breeding does not cause problems. Irresponsible breeders that don't do their research or operate with integrity do.
    Effects of inbreeding and other genetic components on... [Animal. 2009] - PubMed - NCBI

    genetic health and fitness in horses

    Inbreeding Throroughbred race horses leads to breeds demise | Global Animal

    I'm not talking about line-breeding Chiila, I'm talking about a dad breeding his daughter or a mare being bred to her son, in-breeding. Yes, your chances of getting what you want are good, BUT your chances of getting something "BAD" from that breeding are higher.

    I can see how breeding a mare to a sire that is 5 or 6 lines my not cause "problems", and you will probably get what you were breeding for. In all the articles that I've read, even if they were Pro line-breeding, they warn against in-breeding.
         
        09-20-2013, 11:12 AM
      #37
    Trained
    The 2 yo Babson bred colt I is cow hocked. Pretty badly I might add. I bought his mother when she was in foal with him. She has very good legs. She had been turned out with a stallion and already produced a colt with him. He too was cowhocked.
    Researching the stallion I discovered he and a few other foals he sired are cow hocked. Not as bad as my colt.
    If I ever bred her to another Babson bred stallion to keep the line going in my herd I would find one like Lady my mare with straight correct legs.
    This years colt she had is very very correct. The outcross to my stallion was very successful. They are distantly related 4 generations back.
    I believe firmly in breeding related horses. My family has done so with cattle for generations with great results.
    Yet I follow the rule my family has. I might breed father to daughter or grand father to Grand daughter but I would never breed those offspring back to their father.
    Star has sired 5 fillies with my mare Dancer his half sibling. All have been correct and very nice horses. I would never breed one of those fillies back to their sire or a half sibling.
    The fault has to be present genetically to be passed on so as Chillaa explained inbreeding does not cause defects. Shalom
    Druydess, doubleopi and EliRose like this.
         
        09-20-2013, 11:17 AM
      #38
    Yearling
    http://journals.cambridge.org/downlo...b278dbfe6e39fd

    I found the whole article
         
        09-20-2013, 11:21 AM
      #39
    Green Broke
    Here's a few articles I had just posted on Psynny's thread. They explain the entire concept pretty clearly:

    Inbreeding, Linebreeding and Crossbreeding

    http://tylerligon.tripod.com/sitebui...anbreeding.pdf

    Breeding any relation can be successful if done correctly.

    Quote from the article mentioned above:

    Fortunately for us, there are still a small
    Percentage of Arabians that contain only
    The blood of the original Bedouin desert
    Steeds. Again, I will use Sheykh Obeyds
    As my example but there are other
    Subgroups that have remained pure. SO
    Arabians came from the Bedouins out of
    The desert and have been bred on without
    The infusion of outside or impure blood.
    This allows us a resource that continues to
    Be void of most undesirables or recessive
    Disorders. To this day there are no known
    Cases of an SO Arabian dying of SCID or
    LFS. Since there is little chance of these
    Traits showing up, we can utilize
    Linebreeding and Inbreeding to their
    Utmost potential to produce extremely
    Prepotent individuals who will produce
    Consistently for us. Consistency is one of
    The hardest things to come by when
    Breeding horses and it is the hallmark of
    All great Arabian breeding programs.
         
        09-20-2013, 11:22 AM
      #40
    Yearling
    Another thought. By in-breeding, and essentially limiting the gene pool, aren't you eliminating the possibility of introducing more desired traits? Such as immunity, stronger legs, etc.?

    So in essence, by limiting the gene pool aren't you contributing to the downslide of a breed by preventing sustainable diversity?
    Shoebox likes this.
         

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